What is Handling?

peter pyce

Veteran Member
Joined
Nov 6, 2001
Few more and we are done with the copy-paste and then will extend with "modern" from 2006 thoughts..... Ceilidh all the way to the end:

7. Roll Centers and Weight Transfer

We're going to eventually get to the GT suspension, but there are still a few odds & ends to clean up. For this installment, you can decide whether you'll want to read it by first seeing how you do on a little quickie quiz:

Answer True or False:

1. Reducing the amount of body roll while cornering will improve performance by reducing the lateral weight transfer on the tires.

2. When a car rolls, it compresses the springs on the outside tires, which overloads the tires and reduces their effective traction. A car that rolls less will compress the outside springs less, which will load the tires less, which gives them better traction.

3. If you lower a car, it will roll less.

4. If you drop the front roll center and keep everything else the same, the car will understeer more.

5. Springs and antiroll bars are the primary factors that determine how lateral weight transfer is distributed fore & aft (which, together with camber effects, determines whether the car understeers or oversteers).

Ok, did you take the quiz? Honestly? With no peeking? Ok, then here are the answers:

(drum roll please....)......If you answered anything other than "False" for all of the questions, and if you care about suspension theory, you might want to read parts of this installment. =)


1 & 2 -- Why Reducing Roll Does Not Affect Weight Transfer

Ok, first thing is to get lateral weight transfer squared away: when a car goes around a corner, weight is transferred from the inside tires to the outside tires, and the amount of weight transferred is equal to:

(lateral g-force) * (car mass) * (CG height) / (track width)

Note that spring rate and antiroll bar rate have nothing to do with it. When a car goes around a corner, the weight transfer will occur regardless of whether its suspension is pillowy soft or absolutely locked solid. Making the springs stiffer will not reduce the weight transfer, and thus stiffer springs will not directly make the car perform better (if there's a performance benefit, it's an indirect gain from less tire camber, better control of unsprung weight, or less body movement over bumps, etc., as discussed in earlier installments).

Similarly, roll doesn't enter into the equation either (to be really accurate, it actually does to a very small extent, in that the CG shifts sideways when the car rolls -- but whilst this is a concern for big SUVs, buses, etc with a lot of roll and a very high CG relative to track width, for our cars it's small enough to basically ignore). Roll can do a lot of horrible things for handling (via tire cambers, body transients, etc.), but weight transfer is not the main issue. Hence any spring vendor that tells you that "stiff performance springs reduce weight transfer by reducing body roll" is either (A) clueless or (B) dishonest; either way you'll not want to trust him.

(Aside: So what does affect weight transfer? Track, and CG height. Here, for once, the advertising arguments do have a physical basis: if you drop the CG, you'll reduce the total lateral weight transfer, and if everything else stays the same, your handling will improve. Similarly, if you widen the track, you'll get less transfer, and if everything else stays the same, your cornering power will improve. That's why true race cars are built with the CG as low as possible and with the track width usually at the limits of regulation.

The hitch of course is the phrase "if everything else stays the same": Everything else never does stay the same. Dropping the CG by installing lowering springs causes a host of problems (discussed in this thread and more completely in the forum stickies). Widening the track by installing huge wheel spacers will destroy your bearings and screw up your steering geometry, which is also slow. All in all, "improving" your car by reducing weight transfer is not a good way to begin.)


3. Why Lowering Doesn't Necessarily Mean Less Roll

Here's another issue that has been amply discussed elsewhere, but on the off-chance there are novices who have been reading about roll centers, but don't really know what they are, here's a (very) abbreviated explanation:

a) Imagine a car with solid axles (meaning, there's literally a big beam running at hub-height from left wheel to right wheel, straight across each end of the car). Now imagine that you've drilled a horizontal hole straight through the midpoint of each axle, and that you've bolted the body of the car to the axles using those holes. If I've painted the picture correctly, you have a "suspension" where the wheels on each axle can't go up & down together, but they can pivot: if the left wheel goes up, the right wheel goes down, and vice versa. Set this strangely designed car on a level ground, steer it around a corner, and it will roll -- and the axis about which the car rolls will be the centrepoint of each axle (because that's where the body is bolted to the axles). In this situation, the axle centrepoint -- where the body is bolted to the axle -- is the "roll center".

b) In situation "a", the roll center is a physical thing -- you can see it and touch it, and it's really easy to see how the car rolls around it. There are some cars (well, there used to be...) that have such a physical roll center (chiefly some DeDion suspensions from WWII days), but unfortunately (for visualization purposes) that's not the norm. Nowadays we have suspensions where the roll center is not a physical pivot point, but a "virtual" point that moves around as the car shifts about on its suspension. But although the roll center is typically a virtual object, it controls the car's motions exactly the way that a physical pivot does. So if you have trouble imagining what the roll center does to a car, just imagine a solid, physical pivot sitting where the roll center is said to lie....

c) Now let's do some physics (shudder): suppose the car body in "a" has a center of gravity that lies 18" above the ground. How do we get it so that this car does not roll at all when it goes around corners? That's easy: we give it 36" wheels (overall diameter, wheel & tire together). In that situation, the physical roll center is sitting at 18" (axle height), which means the center of gravity (CG) is sitting directly on the roll axis (sorry -- the "roll axis" is the line connecting the two roll centers -- here it's a horizontal line running fore & aft 18" above the ground). Since the CG is sitting on the roll axis, there's no tendency to roll. So the car corners flat -- even though we don't have any springs or antiroll bars.

d) What happens if we make the wheels, say, 48" in diameter, so that the CG of the car body (at 18") is lower than the roll axis (at 24")? That's interesting. Now the body of the car is basically hanging down from the roll centers (from the physical pivots, in this example), and it'll actually bank into turns, the same way a bucket will "bank" into turns if you carry it by the handle.

e) Conversely, what happens if we drop the roll center way down, all the way to the ground? The car rolls, a lot, as now the CG is above the roll center.

f) In practice, automotive roll centers always like below the CG (situation "e"). Given that, a car's tendency to roll depends upon how far the CG is above the roll center. The greater that distance, the more the car wants to roll.

g) Now, if you go to the "Lowering" sticky at the top of the forum, you'll see that if you lower a McPherson strut suspension, the roll center drops faster than the CG -- which means that the distance between CG and roll center grows, which means that you have more tendency to roll This phenomenon is really well-discussed elsewhere, so we'll say no more about it.

h) What we will mention in passing, however, is what happens at the back of the Golf/Jetta IV: for everything other than the R32, we have a twist beam rear axle, and the roll center in such a setup lies right in the middle of the twist beam. If you go look at this axle on your car, you'll see that it doesn't behave like the McPherson front: if you lower the rear of the car, the CG drops (because you're lowering the car), but the twist beam doesn't drop quite as much (because of the way the trailing arm is pivoted: the wheel end doesn't drop at all, while the pivot end drops with the body....and the twist beam is in between). Hence when you drop the rear end of these cars, you simultaneously lower the CG while slightly reducing the tendency to roll. Thus you're free to lower the rear end of the car pretty much all you want -- theoretical roadholding will improve because of the (modest) reduction in roll and (modestly) lowered CG.

And so, if you've ever wondered why the Shine setup looks so, um, interesting, that's why: Shine keeps the front high, for all the roll center and camber gain issues discussed in the previous installments, while dropping the rear for less weight transfer and less roll.

(continued next post)
 

peter pyce

Veteran Member
Joined
Nov 6, 2001
(continued from above on Roll Centers and Weight Transfer)

4 and 5) Roll Centers and Understeer / Oversteer

First off, let's be hastily clear: if you blithely lower the front of you Golf/Jetta IV, it will understeer more -- that's because you'll drop the roll center faster than the CG falls, the car will roll more, and the front tires will go more into adverse camber. But the question in #4 was subtly different: it was asking what is the effect of roll center height on understeer/ oversteer?

If we had a way to drop the front roll center without changing any other parameter: the car somehow rolls exactly the same as before, the spring rates are the same, the CG lies at the same point, etc., then the car will understeer less than before. For the front of the car, this kind of a moot point -- we have no way of dropping the roll center without screwing up the roll, and there are many good reasons in any case for keeping the roll center where it is -- but it's of interest for the rear, and we'll get to it via our solid-axle thought example:

a) Remember our solid-axle car with the body physically bolted to the axles? Think back to the case where the wheels are 36" in diameter and the CG is at 18" -- this is the car where the CG lies on the roll axis, and the car won't roll at all in a turn, even if it has no springs.

b) Will there be lateral weight transfer when this car goes around a corner? Absolutely -- like we said before, there's going to be weight transfer regardless of whether the car rolls.

c) Ok, next question: if this car has no springs, but there's weight transfer....what exactly is causing the weight transfer to occur? We usually think of the car rolling, and compressing the outside spring, and thus putting more weight on the outside wheel, but here there's not spring -- and yet there's weight transfer. So what gives?

d) The answer is that the roll centers themselves cause a lot of the weight transfer to occur on a car.

e) If the roll centers are up at the CG height, all the weight transfer (more exactly, all the transfer for the sprung mass) goes through the roll centers, and none of it goes through the springs. If the roll centers are on the ground, then all of it goes through the springs, and none of it goes through the roll centers. If the roll centers are halfway between the ground and the CG height, then half of the weight transfer goes through the roll centers, and half of it goes through the springs. And so on. The higher the roll center, the more weight transfer that goes through it.

f) Hence, if you keep springing constant, and play with roll center heights, you can change the fore & aft distribution of weight transfer. Start with a neutral car with 50/50 weight distribution, uniformly high roll centers, equal springs front & rear, etc. Drop the roll center in the front and raise the roll center at the rear, and more weight is transferred at the back, so the car oversteers. Raise the front roll center while dropping the rear, and you get more front transfer, and hence you get understeer.

f) The reason most of you have probably never read about this phenomenon is that on most performance cars, it's not an issue. There are many good reasons to design a suspension such that the roll center is just above the ground. If you do this, not a whole lot of weight transfer goes through the roll centers, and the weight that does is pretty balanced (because both front and rear centers are uniformly low). Thus if you spend your time reading about performance car suspensions (and who wants to read about non-performance car suspensions?), you won't hear much about roll-center effects on lateral weight transfer.

g) Unfortunately, however, the Golf/Jetta IV has a twist beam rear suspension, about which Milliken & Milliken are only able to say (p. 661): "This family of rear suspensions is....used on front wheel drive cars. The only time one would be on a racing car is in a showroom stock-type class."

For this suspension, the roll center (up in the twist beam) is unusually high. On my GTI I've measured it at 8.5"; on a brand-new Golf it'd be at around 9.5". This height is not quite so extreme as what you'd find on a vintage British race car (on my MGB it was about 12"), but it's still high enough to cause a lot of weight transfer that has nothing to do with the springs. On my MGB (for which we knew enough to do a reasonable analysis), over half the weight transfer at the rear was due to the roll center height, and less than half was controlled by the springs. For the GTI (for which nobody seems to have reliable information on even basic things such as stock spring rates), I would guess that maybe a third of the weight transfer if roll-center-controlled.

What does this mean? We'll use this tidbit in later discussions, but for now it's just another reason why if we want to appreciably improve the Golf/Jetta IV suspension (for handling), we should be focusing on the front. Simply put, there's a lot of lateral weight transfer already occurring at the back of a Golf/Jetta IV: in addition to the springs, the twist-beam, and the stock antiroll bar inside the twist-beam, we also have a really high roll center that's throwing an awful lot of weight onto the outside wheel -- and with all that, the car still understeers a ton under hard cornering. When you read a tuning guide urging a stiffer rear to curb understeer, the guide is generally assuming you're starting with only a moderate amount of rear weight transfer in stock form, in which case a small change can have a big effect; with our cars, however, we start with a lot, and there's only so much stiffening we can do back there before we start getting into pathological cases (note: we're not saying that stiff rear bars aren't good -- but if you want to use a big rear bar, you ought to stiffen things at the front first).

Or to put it a different way: apparently this thread really got going when Peter Pyce went to stiff fronts and a soft rear, and many people told him he was crazy, that he would understeer off the road, that there was no way this suspension could work, etc. These people assumed (quite reasonably, given everything that's written out there) that such a setup would cause much more weight transfer in the front than in the rear, which would cause massive understeer. But in fact, there's a heck of a lot of weight transfer occurring at the rear for purely geometric reasons, and it's possible that in stock form there's already more transfer at the rear than at the front (no, I haven't done an analysis, so I'm not sure -- it's not an uncommon situation, however, for passenger cars with a high rear roll center and an overall abundance of stock roll); if so, the only thing keeping the stock car from oversteering off the road is the extreme amount of tire leaning that takes place at the front while cornering. By putting on stiff front springs, Peter has probably brought the F/R lateral weight transfer distribution closer to a more traditional balance (with the front maybe 10% more than the rear), while keeping the front tires more upright through reduced roll.

Anyway, all the above is just a conjecture until we can build a spreadsheet model (if ever). Next installment will finally get into GT suspensions, now that we have all the conceptual tools. See you all next week!

- Ceilidh
 

Ceilidh

Member
Joined
Mar 12, 2006
Regrouping (continued)

Oh my -- I'm not keeping up with Peter's cutting and pasting!!

Here's what we'll do for now: let's conceptually divide this thread into two separate subthreads. One subthread is the cut & paste, consisting of rather long, quite detailed explanations of suspension theory -- call that the "Deep Knowledge". The other thread is what we're composing in 2006 for you, dear TDI reader :), these posts are intended to be a little more accessible to the normal non-physicist enthusiast. Hopefully if you can keep these themes separate in your mind, you'll be able to make sense of things!

Anyway, moving right along (with the backlogged comments):

3) bhtooefr and 4Vdubs:
We'll (hopefully) get to your topics, all in good time! bhtooefr, I had an A2 before my current A4 GTI, and I know exactly what you mean: the A2 was a much better darter chassis! It was better not because it had less inherent understeer, but because of its much more immediate agility (which we'll get to in a few weeks -- sorry for the delay), which among other things allowed one to throw it briefly into oversteer almost at will (while retaining lots of background understeer so that these brief fun oversteer moments didn't lead to catastrophic trips into the shrubbery). Along those lines, 4Vdubs, if you want to do some experimenting and reporting back to the masses, try this sometime: find a nice, big, empty parking lot with nothing to hit, and drive a smooth big circle (essentially, do a skidpad run) until the car is maxed out; then do sort of the same on a smooth dirt road curve (again, with nothing to hit!!). If your experience is similar to those of Peter's (in a slightly different context), you should find that you have more oversteer on dirt than you do on smooth asphalt (though if the asphalt is bumpy, you might have oversteer there too). If it's not perfectly safe, don't try any of this! But if you have a chance, let us know what happens (and if you get a different result, please let us know exactly how you performed the test, as these variances are extremely useful!).

In any case, I have a feeling both of you might be interested in the agility section, which is forthcoming...


4) Golf_GTDI

Yes, let's ask Peter for pictures & animations! (And I really look forward to hearing more reports-from-the-field from you -- thanks for posting!)


5) BoosTDIt

Agreed -- A2s make great darters!! (I so miss my A2 Golf sometimes....)


6) oldpoopie and IndigoBlueWagon

Sigh. I never thought of myself as an older veteran, but your posts made me realize that, yes, I'm no longer one of them young whippersnapper types with their new-fangled iPod thingamajigs, no sirree....

Anyway, very glad to have met some folks who can understand!! I learned to drive in a Slant Six Dodge Dart, and my first car was a Spitfire (with 145/80-13 tires in the rear, and 155/80-13 in the front -- talk about oversteer!! I used to love roundabouts (there were tons of them in Newcastle upon Tyne): downshift to second, turn in, nail the throttle, and gosh the rear end would skate! A friend had an 850 Mini, which was a riot on the singletrack along the Scottish borders, and another friend had a (post-Frogeye) Sprite, in which he took me on the fastest slow-motion city drive I've ever been on: it was in London, and at every intersection he had the rear end far, far out (he was a better driver than I) -- and at no time did we deviate from the normal traffic flow: as far as the Bobbies could see, we were just driving long with everybody else.... Oh(!) -- and the high point of my university year was a visit to the Westfield factory (dragging along another non-motoring roomate), where they gave us test rides (they drove, we rode) in their Lotus XI replica (no windscreen, no helmet): during my ride, I asked the driver "Can you hang the tail out?", thinking he'd do it at the next corner, and the guy said "Sure!", jerked the wheel on the straight, and we were suddenly at a 20-degree drift at 80mph...

(Oh, for all you young whippersnappers: with these old sportscars, oversteer didn't have to be noisy. You could bring the rear end out, and hold it out, without the tires making any unusual sound at all (at least nothing loud enough to be heard over the general sound of an English car continuously falling apart -- these things didn't have Japanese or German build quality). I wish there were some way to magically teleport you all back in time, and put you in these cars (someplace in Europe): they were safe, slow, fun, and incredibly, incredibly responsive to what you did as a driver. Drive them badly, and they handled really badly; drive them well, and they made you feel like a hero.)

Digressionary Note #5:
Even among automotive journalists, there's a generational divide on what makes for a good-handling car. The older folks (e.g., George Karcher with "Car" and "Autoweek", Dennis Simminaitis and Peter Egan with "Road and Track") don't care very much about how much grip a car has; in many ways, they even prefer a car that slips fairly early, so long as it does so progressively & predictably, while remaining responsive to driver inputs. In contrast, the younger writers are all about grip and agility -- how well the tires stay glued to the road, and how much a tug on the steering wheel leads IMMEDIATELY to a change in direction and attitude. Goodness knows why this generational divide exists, but I've a hunch some of it has to do with the cars and tires the writers grew up with: when the older guys came of age, tires didn't grip, and trial lawyers hadn't yet met Ralph Nader, so cars were constantly slipping and sliding, and a fun car was one that did what the driver told it to do (regardless of whether the instructions were good or not); conversely, the young guys all grew up when tires were sticky and literal responsiveness (Driver to Car: "I'm going to use my pedals and steering wheel in a way that will spin you off that high cliff above the petrol station next to the orphanage." Car to Driver: "Yes sir!! Right away, sir!!") was no longer a legal option -- with cars like that, g-forces and (safe) responsiveness to the steering wheel are what make for thrills and fun.

Anyway, we'll never get a Golf/Jetta to handle like a 1950s Austin Healey (heck, even the Miata apparently no longer tries to handle like that), but we'll see if we can get a little more (safe) responsiveness into our cars.:)
 

Ceilidh

Member
Joined
Mar 12, 2006
mea culpa! mea culpa!

peter pyce said:
(continued from above on Roll Centers and Weight Transfer)

......the Golf/Jetta IV has a twist beam rear suspension, about which Milliken & Milliken are only able to say (p. 661): "This family of rear suspensions is....used on front wheel drive cars. The only time one would be on a racing car is in a showroom stock-type class."

For this suspension, the roll center (up in the twist beam) is unusually high. On my GTI I've measured it at 8.5"; on a brand-new Golf it'd be at around 9.5". This height is not quite so extreme as what you'd find on a vintage British race car (on my MGB it was about 12"), but it's still high enough to cause a lot of weight transfer that has nothing to do with the springs.....

- Ceilidh
Alas, there was an error in that Vortex quote of 2 years ago: when I wrote the above paragraphs, I had been lazy, and had simply read some numbers off a published suspension diagram without working through the geometry on my own. And, well, laziness is a bad thing -- when I subsequently plotted things out on a sheet of paper and thought it through, I discovered that (1) there was a misprint on the published diagram, and (2) I was completely wrong.

So here's the correction: the roll center at the rear of the A4 suspension is very close to the ground (just a fraction of an inch above), and it doesn't move very much when you lower the car. Hence with the stock car (which has the front roll center also near the ground), there's relatively little roll-center effect in determining the lateral-weight-transfer distribution, and the latter IS controlled primarily by the springs and bars (i.e., Quiz Question #5 should be answered "True"). But the end conclusion is still valid: when you lower an A4 chassis, the front roll center drops and the rear center stays constant, so you wind up shifting the distribution rearwards.

Anyway, my apologies for the error!

- Ceilidh
 
Last edited:

peter pyce

Veteran Member
Joined
Nov 6, 2001
Sorry Winston, I tried to read everything once again before transferring it here, but that part slipped. I do even remember the following discussion with Dick about this and yet simply did not see through when was reading it again today. Good catch and thanks for reading it again in detail ;)
 

Golf_GTDI

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Joined
Jun 12, 2004
Location
Logan Ohio, USA
TDI
2001 Golf GLS
Thank you folks again so much for bringing this info here. I wish I had better input but for now I'm gonna try to shut up as much possible and just listen and try to understand. As the weather is better and the road surfaces improve I feel I am getting a better understanding of how my current system is working and look forward to working with Peter to help build as true a GT type system as we can get to with our cars. I tend to think that I may be a bit of a GT type in that I find myself enjoying covering distance on fun roads at speeds that tend to be a bit quick but feel that the car is well collected and safe. With that said I think I would like to push past this seeing as I want to get past these limitations as I just don't feel I can find the limits of what I have at this point in a safe way on public roads and aim to spend some time on real tracks this summer.

In short I aim to lend some seat of the pants thoughts with a system that hopefully ever closer to what these folks are trying to build. If you don't mind Peter I may try to give you a call in the next few days to these ends.
 

Nate_Grauvogel

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Joined
Feb 10, 2005
Location
CO
TDI
'15 T-Reg Exec
Ceilidh said:
...

1. Nate, that sounds like a very interesting course that you're taking -- If you come up with any neat insights, do please tell everyone! (What software package are you using? Would you recommend it?). And where in NM did you live? I did the drive up from Los Alamos to Mesa Verde via Chama a few times: what heavenly roads!! Hope you get back out there sometime...
Yes, Ceilidh - a very interesting course. Unfortunately it's been over for a year, and I'm pretty busy finishing up my last three to graduate in May.

It was by far the most fun class I've ever taken. It was actually a course in Modeling & Simulation, but using an auto as the subject. As an added bonus, the prof is a bona-fide car nut. For that semester wei used a Saleen S7... the end goal was to critique/compare our results to the advertised performance specs. Turns out its top speed is RPM-limited... and it could drive upside down if you could find such a road while going fast enough. We played with steady-state grip and transition/emergency lane change maneuvers to investigate effects of springs, dampers, roll bars, and geometries on handling and ride quality. We also did the same for school buses, tractors, etc... the trick is getting all the data to plug in.

A pretty comprehensive overview, but in one semester you have to make some generalizations to keep things simpler (we neglected the effects of changing camber and modeled the clutch as an on/off linkage, for example). Once I finish my degree, I'd like to continue my model-building on my own and add that fidelity... then the hard part is quantifying the actual products out there (including OEMs - they don't like to share, and would tend to wonder about "consumers" asking what the actual damping/spring rates, etc are)

We used Matlab/Simulink... it doesn't get much better than that - endless possibilities. If you can get the student version, you can buy a copy for around $99 (that's what it cost then)... it just doesn't include much support or any updates (really the only way to get that is to be the independently wealthy, mad scientist type, or work for a company that owns a license - I might be mad, but not wealthy, so I'm stuck with my older version, but it works!)

I lived in Cloudcroft and drove US 82 between there and Alamogordo to work every day: 16 miles + 4,600 ft elevation change + lots of curves = FUN! :D I've been up around Durango/Ouray/Silverton, CO a couple times - also breathtaking.

Well, I've gotta get back to work now... I really enjoy the discussion - Thanks!
 

Nate_Grauvogel

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Feb 10, 2005
Location
CO
TDI
'15 T-Reg Exec
Something interesting

Ceilidh - I forgot:

One interesting thing I haven't heard here yet is talk about natural frequency in steering response... I forget the actual physical ways it's controlled/derived right now, but remember the lesson well:

As vehicle speed increases, natural frequency decreases. In other words, rocking the steering wheel back and forth at, say 1 Hz, doesn't do much but weave the car around at low speeds, like on a city street.... but... if you do the same thing at the right speed, say 70 or 80 mph, you can get a real tank-slapper (to borrow a term from motorcycling) going with one or two cycles. Our professor urged us to try it sometime... it's eerie.

Any fully-engineered setup mitigates pathological behavior, but that natural frequency is still there beneath, no matter what you do. Worn-out components can negate proper controls, though... my old IROC (sold it to buy my TDI :() with worn tie rods and wheel bearings could get very excited and start a nasty steering shimmy when going just the right speed and hitting a bump just so... usually at low speed, 25-30mph, solved by lightly accelerating. But then I once hit the next harmonic at about 60 mph once in a sweeping off-ramp... the rear end started sliding around - scary religious experience... dumb me for driving it worn. :eek:

When I get some time I'll look back through my notes and post a little more about it - not sure how much a factor it is in these discussions, but it's interesting...
 

Golf_GTDI

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Jun 12, 2004
Location
Logan Ohio, USA
TDI
2001 Golf GLS
Nate_Grauvogel said:
my old IROC (sold it to buy my TDI :() with worn tie rods and wheel bearings could get very excited and start a nasty steering shimmy when going just the right speed and hitting a bump just so... usually at low speed, 25-30mph, solved by lightly accelerating. But then I once hit the next harmonic at about 60 mph once in a sweeping off-ramp... the rear end started sliding around - scary religious experience... dumb me for driving it worn. :eek:
I must say that I still honestly wonder about some of the things I am finding in my own system. I hope to see this touched on at some point in more detail.
 

peter pyce

Veteran Member
Joined
Nov 6, 2001
Let’s put some of the key scenarios discussed here into pictures, so it will be easier to comprehend and build from there….

Ceilidh said:
The geometry of the McPherson strut front suspension is discussed fairly exhaustively elsewhere on this forum, so we we'll only briefly summarize the salient points here: when the Golf/Jetta IV rolls on the stock suspension, the outside front wheel (which takes most of the turning load under hard cornering) initially stays fairly upright, but then takes on increasing amounts of adverse camber (i.e., it leans towards the outside of the corner the car is negotiating). This leaning, or adverse cambering, is extremely progressive and continuous: corner lightly, and the tire's pretty upright; corner moderately, and the tire leans moderately; corner hard, and the tire leans a lot.
Here is the front of our cars. Little bit schematic, but the dimensions are correct, so the movements are pretty close to reality. The driver is sitting on the Left side of the animation, so the front is towards the screen you are looking at and the rear of the car is behind your back. The car has both wheels steering to the right, making a right curve, going forward and rolling to the left. So, the left wheel is the left front wheel of the car and the right is, of course, the right front wheel of the car:

(Note: It is a GIF animation, so wait till it loads for smooth view. Sorry for the folks with Modems, there is really no way to animate those things in large format and make them small at the same time)



So, above we have the car from flat (straight line) rolling to about 6 degree towards the left (in a right curve), which is more or less the max roll angles ones would get when going wild. To relate to the text above – we can see how the left tire goes into positive camber pretty dramatically. At the same time, the right tire (inner to the curve) goes into negative big time. Now, with the help of those packages used to model those things, we can record the degrees of total inclination the tire/wheel has in relation to the road. Below is a diagram that puts those numbers (generated from the animation above) in a simple chart, so ones can see what degree of camber we have on the front wheel when the chassis rolls degree by degree:



Let’s concentrate on the dark blue line in the above chart (that line represents the A4 front geometry). This chart is exactly for the above scenario (in the animation) as we have the steering at 10 degree. So, at 0 degree body roll (horizontal axis on the chart) we have about -1.5 degree front camber (This is all on the outer, left wheel only!). The 10 degree steering is the reason the camber is already negative, all due to the caster on these cars, but perhaps will go in depth on that later….. We roll the car one degree and according to the chart the total camber the wheel has now (related to the road!) is about -0,6 degree. Then we roll another degree (to 2) and the camber is already positive (!) at about +0,3 degree. Then 3 degree roll gives us +1.2 degree positive. 4 degree of roll puts us at +2,3 degree and so on, to a total of about +4.4 degree of positive camber at full roll when the car will stop rolling as it will start sliding and no more roll gain will be possible.

(As a side note, a stock car on stock tires may not even get that far as the all season M+S tires should give up a lot earlier and the car will slide instead of rolling. But let’s leave this discussion for later).

Let’s move to the rear now…

Ceilidh said:
….. In contrast, the non-R32 rear suspension is a simple twist-beam with the beam mounted aft of the trailing arm pivot points. Geometrically this suspension behaves much like a semi-trailing arm setup, and the outside rear tire remains relatively upright as the car rolls (at least so long as both rear tires remain on the ground). Thus the geometry of the stock suspension ensures that as the car corners and rolls, the front tires lean (adverse camber) more than the rears, with the amount of leaning progressively increasing with cornering speed.
So, let’s look at this animation, representing the rear twist beam. This time the camera looks from the rear right corner, down on the assembly. The lower right “disc” represents the rear right wheel and the upper left “disc” represents the left rear wheel. The red “beam” is nothing else but representative of the chassis (the car) that we see here rolling left and right. This animation is not as clear as the first (of the front) so if anyone has trouble visualizing the movements we are going to talk about below, let me know and perhaps we can do a different angle animation:

(Note: it is another heavy GIF file, so wait till it loads for smooth view)



Let’s observe the lower right “disc” (as it is closer to the camera and easier to see its movements). It is pretty visible how the “disc” (representing the wheel) gains and loses camber as the read beam (the car) rolls. If we do the same data collecting as per the Front Geometry, then the following chart comes out:



Here we have both wheels (inner and outer) and their related camber gain/loss. We can see the outer wheel starts from -1.65 negative (that is what our cars come with in general as static rear camber), and by rolling at about 5 degree (body roll) it goes to about +1.62 positive! (we are looking at the blue line as that is the one of our interest in this scenario).

So, to put it now together. As per above quote, when the car rolls, the front has to gin more positive camber than the rear per every degree of roll. Let’s put now all the graphs together and see if we have it that way:



The dark blue line is the outer (left) front wheel and the light green line is the outer (left) rear wheel. (both lines derive from the other two diagrams shown so far). So, we can see how the blue line gains a lot more positive camber than the green line as the car rolls, to a point that at pretty full roll at about 5 degree (car roll) we have more than one degree of difference in front to rear camber!
 
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IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
Thanks, guys! I have to confess to reading the VWVortex Suspension FAQ on geometry more than once, and spend entirely too much time thinking about these things. But Peter, you wrote something in your first post that just helped me figure out something about my wagon. I had the SRS setup and thought it rode too harsh, but now understand my problem was the tires. I took out the springs and dampers and now run Koni Reds with the stock springs--but the Shine rear bar is still in place. I'm taking a driver's school this weekend at NHIS and today decided to bring my A3, which has Neuspeed Sofsports, Koni Reds, and a Neuspeed rear bar on the middle setting. Why? For reasons I couldn't explain (until now) I feel more comfortable in the A3. I just felt like I didn't know (or wasn't going to like) what the car would do at the limit. It feels great at 5/10s, but occasionally I feel like I'm headed into no-man's land. And I have lost the rear end (once) in the snow, even with the Shine springs.

Now I know what I was feeling was the approaching terminal understeer when a rear wheel lifts. It tempts me to take the Shine bar out and see what I have.

EDIT: A walk and a cocktail and now I have more ideas. What happens if I keep all else the same but install TT spindles that will keep the front camber (and therefore the grip) more favorable? Will the car still transition to terminal understeer, just at a higher cornering load? Or will it become more neutral at the limit?
 
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Ceilidh

Member
Joined
Mar 12, 2006
a flash forward

peter pyce said:
.......So, we can see how the blue line gains a lot more positive camber than the green line as the car rolls, to a point that at pretty full roll at about 5 degree (car roll) we have more than one degree of difference in front to rear camber!
Despite best intentions, this thread is looking like it's going to jump around a bit(!), but rather than let something pass for too long, here's a little preview:

At some point (a point that steadily recedes in time, what with all the interesting diversions along the way), Peter and I hope to write up a little guide explaining what different sorts of modifications do to different aspects of handling. That "guide" is still a long ways off, but now that Peter's posted these excellent graphs of the A4 camber change with roll, it seems a good time to (briefly) mention the TT front spindle option.

For those not familiar with this option: there exists a reasonably straightforward OEM (VW) modification that will "cure" the "excessively understeering" camber curve in the A4 Golf/Jetta chassis. This mod basically consists of taking the front spindles off an Audi TT, and installing them in place of the stock Golf/Jetta items. Do that, and you have a slower front camber "degradation" with roll, with much less difference between front & rear camber angles even at extreme roll angles. Since the front camber plays such a major role in producing roll-understeer in our cars (because of the camber-thrust effect discussed in the cut&paste), reducing the front-vs-rear camber difference will significantly reduce the understeer in a hard corner, while still keeping the front tires more or less upright when driving in a straight line (which is good for tire wear, straightline braking, street steering feel, etc., etc.). Moreover, because the spindles are actual VW parts, the conversion can be done fairly neatly, with none of the cursing & filing & fudging that normally comes with installing aftermarket "performance" parts.

Sounds good eh? :)

Now, the reason we're bringing up this option now (immediately after Peter's posts and cut&pastes) is that it's a great opportunity to try applying some of the concepts posted up over the last two weeks. The TT spindle option (as regular Vortex readers will likely know) is heavily favored by some tuners & autocrossers/track enthusiasts, and indeed Peter and I would never argue that it isn't a plausible mod for racers and the like.......

But --

How will this mod behave on the street?

Let's apply the concepts. If we look at Peter's graphs, we can see that the TT spindle buys you a little less than 1 degree of camber when the car is rolling 5 degrees -- and (not) coincidentally, 1 degree is roughly the front-vs-rear difference in camber gain for the stock chassis at 5 degrees of roll. Thus the TT spindle comes close to wiping out the differential camber gain: when you install it on the Golf/Jetta chassis, you basically make the front and rear wheels behave similarly in a corner.

Now, earlier we talked about how a racecar suspension (one that keeps both front & rear tires essentially upright in a corner) will feel very strange for the normal non-racer driver: if set up to understeer, it will seem to track solidly up to a point, and then suddenly and irretrievably break away at the front; if set up with oversteer, it will feel solid until the moment that it seems to snap into a dramatic and breathtaking spin. (This behaviour arises because (1) in an upright-wheel car, over- or understeer will set in only when g-forces overwhelm the tires; (2) the transition to the tires' non-linear state is very hard for anyone to detect until he/she has spent lots of time lapping a track at high speeds; and (3) once the overloaded tire "lets go", it doesn't respond very well to further driver inputs.)

In the preceding posts, we discussed this "bad" behaviour solely in the context of an upright-tire racecar suspension -- but the behaviour doesn't hinge upon the tires remaining upright. Instead, the "sudden" breakaway is something that occurs when we rely only upon tire characteristics for producing under- or over-steer. Such is certainly the case for an ideal race car suspension in which the tires are kept bolt upright -- but it is also the case for a suspension in which both the front and rear tires are allowed to lean the same amount: basically, if both sets of tires "lose" the same amount due to camber, then the camber is not affecting the handling balance.

Or in other words, the TT-spindle, when mounted on a Golf/Jetta, makes the car behave in a way reminiscent of an upright-tire racing suspension.

This is great on the track. It is great on an autocross circuit. It is even great for a very attentive, trained driver on the street, or perhaps for a slightly less attentive, less trained driver who never approaches the limits of his suspension. But what will it do for a "normal" driver (or a fatigued highly-skilled driver) at the limit? Well, if the grip is lost via understeer, the car will plow straight off the road, with the steering wheel rather useless. If it's lost via oversteer, it will be the sort of oversteer that most non-race drivers have never experienced: if the driver tries to slow down, via braking or even via reducing engine power, the car will not stabilize (the way that the stock Golf/Jetta is designed to stabilize), but will instead snap spin (this because any attempt to slow down will transfer more weight to the front tires, giving them more traction, while further unweighting and reducing the traction in the rears). Indeed the only way to stop a spin once oversteer sets in (with a FWD car on such a suspension) is to apply more power -- not something that comes naturally to anyone(!).

It's for the above reason that yours truly (Ceilidh) has no intention of ever trying a Golf/Jetta with a TT suspension: I'm sure the car will feel absolutely marvelous up to the moment that the tires let go, and I'm equally sure that (my racecar days being many years ago) my current skills and reflexes will not suffice to catch the slide or spin. On a racetrack my incompetence will be embarrassing; and on the road, well, I don't like hitting things.

Final Point:
Regular Vortex readers might recall a sort of TT-spindle forum war about two years ago: basically, there were respected individuals who had worked out how to perform the conversion, who had tried the mod and loved it, and who were urging others to try it; on the other side of the fence was/is yours truly, who feels that this is essentially a dangerous mod that should not be sold for street use. The war came out as a sort of draw (nobody changed their positions), and you, dear TDIclub reader should form your own opinions (should you ever contemplate this mod for yourself), but I'll leave you with an historical tidbit, coupled with a bit more theory:

1) VW owns Audi, and is entirely aware of what the TT spindle will do for the A4 chassis (they have to be aware -- they're the ones who designed and built the spindle!). And yet they have chosen not to mount it on the ordinary Golf/Jetta -- presumably there's a reason.

2) Besides shifting the Golf/Jetta towards an upright-tire suspension feel, the TT spindle conversion will reduce the Golf/Jetta's inherent understeer -- particularly at high cornering loads. Thus in contrast to the stock suspension, which badly wants to understeer when cornered hard on dry pavement, a TT-modded car will be much more easily prodded into oversteer, should the driver do something wrong....

3) The classic oversteer-promoter on dry pavement is a driver who, upon realizing he's come into a fast corner with too much speed, attempts to slow down by easing off the power. When he does so, the forward weight transfer (from decelerating) reduces the rear grip, causing oversteer. The amount of weight transfer (and hence the violence of the oversteer) depends partly upon the severity of the deceleration, and partly upon the car's CG (center of gravity) height: the higher the CG, the more violent the weight transfer, and the more sudden / stronger the transition towards oversteer. Because the CG in a Golf/Jetta is higher than the CG in an Audi TT, the "lift-throttle-oversteer" in a TT-modded Golf/Jetta will hence be stronger and more sudden than it would be in a comparable Audi TT....

4) When the Audi TT was first introduced, journalists and reviewers praised the sharpness of its handling. But then TTs began crashing, with a lengthy spate of accidents (with injuries and deaths) all stemming from sudden oversteer and spins, particularly in Germany, among drivers who were not trained racecar drivers, but who were instead individuals who had learned to drive fast on street-tuned cars (i.e., cars with progressive and stabilizing understeer). Within the year, Audi recalled the cars, enacted a comprehensive suite of suspension modifications, and installed electronic stability control. The public explanation for the oversteer was aerodynamic instability (which probably played a factor), which was "cured" by a retrofitted rear spoilier --- and yet, all subsequent tests of the TT showed the car to have lost its handling sharpness at all speeds: the car simply understeered more, had slower responses, and was much harder to steer on the throttle.

So in putting pieces together: if someone looks at Peter's graph and tells you "Obviously you'll want to fit TT spindles to your A4 Golf/Jetta, as those spindles will cure your understeer and make your car handle like a dream!", consider the above: VW itself is unwilling to fit this modification, one that will dramatically reduce the car's stabilizing understeer at all speeds -- but particularly at the highest speeds and cornering loads. The modification will likely give the Golf/Jetta a more violent and more sudden transition to oversteer than is felt by the Audi TT -- and the Audi TT itself, when first given these spindles, had an oversteer transition too violent for German drivers, and presumably too sudden even now (after a host of chassis mods) for the car to be sold in the U.S. without electronic stability control.

Kind of interesting, what one can deduce via Peter's graphs, yes? :)

Cheers folks!
- Ceilidh
 

Ceilidh

Member
Joined
Mar 12, 2006
IndigoBlueWagon said:
EDIT: A walk and a cocktail and now I have more ideas. What happens if I keep all else the same but install TT spindles that will keep the front camber (and therefore the grip) more favorable? Will the car still transition to terminal understeer, just at a higher cornering load? Or will it become more neutral at the limit?
Hello Indigo!

Your edit was well-timed! -- you must have put it in while I was writing the above post.:)

In answer to your question: whilst I'm uncertain whether the final state will be terminal understeer or terminal oversteer (it'll probably still be steady-state understeer, given the car's weight distribution), we'd expect the on-the-limit handling balance to be less understeering than stock (i.e., probably more neutral at the limit).

Once again, this would be an interesting experiment to try for a track or autocross car -- but on conceptual and historical grounds, it's one that would make me very, very nervous on the street.
 

Golf_GTDI

Veteran Member
Joined
Jun 12, 2004
Location
Logan Ohio, USA
TDI
2001 Golf GLS
As a person who not only has a TT front end but one who has it without a FSB on OEM springs and dampers I will say that it can be a bit of a handfull. The "snap" feeling is in fact there and it seems to happen to me most often in the 65mph range in soft turns (I don't have the nuts nor have I been in a situation to turn hard at this speed on public roads. Please don't ask me too). I can now replicate it almost at will and can drive it out without too much fuss but I can recall the effect it had on my colon the first time I felt the rear go away... gulp.

I can also say that for me I would not go back to a stock front end. I adore the way the car tries to claw to the inside of most corners and the flat crisp grip the car gives no matter how far it rolls over. The only thing that the car seems to be limited by is tire grip and my skill... I'll not give that up easily.

One observation that my wife made the first time she drove the car that I was that it seemed to wander more on the freeway. I did not notice it as much at first because I was so smitten with everything else but I must admit that the car does need more attention in some situations and her observation has merit. It may also have to do with the winter/ice tires on the car at the time.

I don't tend to like to see my wife drive the car as much as I liked too in the past and agree that this is now a car that demands respect and care. Some of us with RallyVW aim to work with Peter on the side to get these issues in check and after trying to spin my car like a top many many times I think that better dampers will do a lot for the attitude of the car in this dynamic situation.
 
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BoosTDIt

Veteran Member
Joined
Jan 14, 2003
Location
DC area - Fairfax,VA
TDI
The Last NA 2dr 5sp
now i just wanted to point out an intresting fact...

R32 - 4WD or not, it's a Golf....yea it comes with ESP only ..but
still a Golf body shape and weight, airdaynamic
TT quattro - we all know about that one.....
TT FWD - how about that ha FF...???

spindles - same part number on all of them
 
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IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
Couple of responses:

BoosTDIt: Yes, the R32 has the TT Spindles, but it also has a fully independent rear suspension that provides better camber characteristics than the other VW A4s. Also, the TTFWD, IIRC, was the car that was causing problems for the German drivers, and I think that car had the same rear suspension as our VWs.

Cielidh: I have to wonder if the transition to terminal understeer would be as dramatic as you stated. If you look at Peter's chart above, and charts in the Suspension Geometry FAQ on Vortex, all the spindles (TT, H2, stock) transition to positive camber, just at different degrees of roll. What's hard to gauge is how that curve feels behind the wheel: what looks like a progressive transition my be experienced as very abrupt.

So what's ideal? A setup where the front and rear lose traction at the same time? Or very mild terminal understeer/oversteer? And how can we set our cars up for that?

It seems that the VW stock opton of a gradual transition to terminal understeer (plenty of warning) is safest. It just isn't a lot of fun because the cornering limits are lower.
 

Ceilidh

Member
Joined
Mar 12, 2006
First, a general comment:

For a year now, Peter's been coaxing me to come visit the TDIclub forum, and now that I finally have, I wonder what took me so long! You folks have a really nice culture here, and I thank you all for the very kind welcome you've given to a non-TDI visitor. :)


To GTDI:

Here is one example of what makes this forum so special! I posted my TT-spindle aside late last night, and this morning there's a commentary from someone who has first-hand experience with the mod!

GTDI, please do tell us more! In particular, what are the situations that bring the tail around (i.e., what do you do to encourage it?), and how do you drive out of the situation? Do you need to "toss" the car, or can you bring it out with a little throttle lift mid-corner? Can you drive through it with steady throttle and countersteer, or do you need to feed in more power? When you say it happens at 65mph, can we assume that it would continue to happen at higher speeds, or do you mean there's a speed band in which it occurs?

(I'm asking these questions partly because it's just neat to hear experiences, and partly because we Theoretical Types (sorry, Vortex Refugee insider joke :)) crave real-world data --- experiences like yours are what helps people like me (and Peter) in refining, extending, and correcting our models. Many thanks for your comments!)

And yes, the grip and mid-corner steering feel is pretty nice, isn't it! It's amazing how sweet and "solid" a front end can feel when the camber isn't trying to swing the nose wide. It can be pretty addictive!

.

And to Indigo (whose posts are another example of what makes this forum so enjoyable):

IndigoBlueWagon said:
Couple of responses:

Cielidh: I have to wonder if the transition to terminal understeer would be as dramatic as you stated. If you look at Peter's chart above, and charts in the Suspension Geometry FAQ on Vortex, all the spindles (TT, H2, stock) transition to positive camber, just at different degrees of roll. What's hard to gauge is how that curve feels behind the wheel: what looks like a progressive transition my be experienced as very abrupt.

So what's ideal? A setup where the front and rear lose traction at the same time? Or very mild terminal understeer/oversteer? And how can we set our cars up for that?

It seems that the VW stock opton of a gradual transition to terminal understeer (plenty of warning) is safest. It just isn't a lot of fun because the cornering limits are lower.
1) No, I wasn't very clear in what I wrote (it was late at night, after all!). If a car has upright-tires or has identically-cambered tires, AND if that car has been set up with strong steady-state understeer, the terminal understeer can be pretty fierce(!). But that's not my concern with most Golf/Jetta IV TT-conversions, as what worries me is the potential oversteer, not understeer.

(To elaborate a bit: Peter's graphs actually show some differential camber gain in roll, even with the TT-spindles (that is, the front tire will still lean more than the rear in a corner) -- the differential is simply much less than before. Hence the car will still have some progression to understeer: it'll be much less progressive than stock, but there'll still be some warning. Also, street tires are much more forgiving in this respect than race tires, and the tires alone will make it more like a transition and less like an On/Off switch....)

(Also to elaborate: it's not the transition point to positive camber that controls everything, so much as it is the relation between the front versus rear camber. You could, for example have the front tires in positive camber all the time -- but if the rear tires take on excessive camber in roll, you'll still get oversteer.)

(And a personal aside: the Triumph Spitfire had front positive camber at all times, but it had a rear suspension that would throw the outside rear tire (which normally had negative camber) strongly into positive camber if you decelerated in a curve. The first time (and only time) I ever braked in a corner with that car (there was a sheep in the road), the effect was as if someone had violently jerked the steering wheel 90 degrees -- that is, the steering wheel itself didn't jerk (it fortunately was countersteering!), but the front end darted inwards (and the rear end darted outwards) with amazing suddenness. Years later, I can still remember that moment of youthful terror (but don't worry -- the sheep was fine)...)

2) The "ideal setup" is something that people argue over with great passion, so I won't get into that here! But in general terms, the more one can soften the lift-throttle oversteer effect in fast turns, the more we can remove understeer. One of the many interesting things about Peter's damper experiments is that dampers have a powerful effect here: when you decelerate in a corner, the initial forward weight transfer is almost entirely due to the shocks, and it's possible that careful shock tuning might soften that transition. So let's wait & see what Peter et al come up with this summer!
 

peter pyce

Veteran Member
Joined
Nov 6, 2001
Let’s look for a second on what the engineers have to accomplish for our streets car (often cursed for “bad” handling)….

Little bit background here: In Europe (for those who do not know) things are little bit different when it comes to car magazines and doing tests for new cars on the pages of those magazines. It is little bit controversial, because in America safety is always advertised so much, it would seem that it is really priority number one for the American buyer, yet the magazines (Car and Driver, Road and Track and you name it) barely include “safety” tests in their reviews. I put the “safety” in comas, as I did not mean the safety crash tests they perform, but tests that would show how safe a car is in panic situations, trail braking, lift over steer, etc. After all, those are the things we have to deal with almost every day and if it is not every day, then perhaps it is once in a five years time, but at that one time yours (and other’s) life can be on the table. So, in Europe, it is a lot more about how fast the car can go with the pedal to the metal, what is the fuel consumption (very important the poorer you are!), what is the power, etc. Only these days the safety talks are going more and more into people’s heads and only these days the big billboards that advertise cars start talking about safety, airbags, bla, bla – before was just some nice chick on the hood and there you go. I even remember few years ago some friends had to replace their older cars with newer models and were afraid of buying something that has airbags, because those things with the mini-explosive inside sounded just scary to have. At one point there was even this “wave” among young German guys, to go and steal a “modern” car that had airbags and go and smash the thing into a tree as to experience what it is like to have an airbag explode in your face. But even back then (more than 10 years ago), the European magazines were already performing all sorts of tests that show the true colors of the tested cars in every day situations that we have to deal with. And here are some of those tests, that they continue performing till today (and I hope will continue performing in the future), so we can put all the talks in this thread into a few scenarios, etc….

So, this first test I wanted to talk about is pretty interesting and speaks so much about why the makers set the cars the way they are. It is from an Italian magazine (called “Quattroruote”, which means “Four wheels”) and is perhaps the benchmark magazine for cars in that country. Comes out every month, but it is thick stuff, about 400 pages and every month they have few new cars to test, but the tests are pretty serious stuff, usually covered on about 10-14 pages, and when it comes to the “handling” tests, here is part of what they do:

Test 1.

Below we have the scene. It is curve with 170 meters of radius, set with cones as shown in the picture. The car drives on the outside of the curve (right) and goes through a photocell (it says there “Fotocellula”). Then it has another 5 meters till the last cone after which has only 20 meters to change lane and move to the left line (as to avoid the diagonal cones on the right lane). Once the cones are avoided, the car has to also remain in the left lane and not touch the series of cones that are on the extreme left border of the lane. It is basically a quick left and then quick right to align. Here is the scene and below an Opel later generation (Signum) negotiating the task (and for the records, the Opel manages 102 km/h max speed and that is with ESP, which in the car is impossible to switch off):



Now, the task here is this – To go through the photocell at the highest speed possible, after which the drive lifts the throttle and also manages to go through the cones without knocking down even one. (Those diagonal cones on the picture are all down, so the cameras can get good details on the tires, etc during every centimeter of the test). Basically, the driver has to do all he wants, but the highest speed at the photocell has to be achieved before cones start flying…… So, in reality, what we have here is a typical lift-throttle, obstacle avoiding situation. What makes this test interesting is that they have kept the piece of track for like 20 years now and nothing had ever changed, so all cars go on the exact same surface and configuration, making the tests a lot more reliable when it comes to comparing different cars through the years….

I have to go back and look for numbers, so you all see some interesting results, but on top of my head I remember that the Golf had been shining for years on that test. The A4 platform was a bench mark for its class for years and the rest of the manufacturers had to come out with electronics as to get even close to what the Golf A4 was offering! Later in the game some of them managed to get close (but with a lot more sophisticated suspension solutions!), but then VW introduced the Golf V, and guess who’s leading this test again! And it is not only in its class, but the Golf V is actually ahead of very well known cars for their “handling” capabilities. I will dig the numbers later as it is really interesting to see the ranks….

Then there is another one, a lot more simple (at first glance) but where the big mess happens from time to time:

Test 2.

This one is called (translated directly) the “The Elk Test”. If I am not wrong it was originated in the Scandinavian countries, where you would drive on this small two lane road in the night and suddenly there would be an elk in front of you, so you have to go quickly left-right-left and avoid the elk, without going out of the road. Here is the scene and a Lexus SUV pictured below going through the actual test:



This, by the way, is the very famous test on which the famous Mercedes Class A failed badly (rolling over!) and then the sky felt down, but I would love to give the microphone to Winston as I remember he had some interesting stories to tell about that Mercedes fiasco. Fact is, there are few cars that failed this test through the years. The very recent one being the Dacia Logan (a Romanian made Renault, econo car for the masses, which is really not bad for the money, as you better have a car than nothing, but who’s suspension I guess was made compromising too much, to fit a budget I am sure, so the car rolled in this test). Here is a picture of that same Dacia Logan at the same exact test:







Why all of the above? Because these two scenarios (and many others) are actually what really matters when it comes to a street car, meant for the masses, just like our cars are. Those guys in Wolfsburg spend years of developing the cars and it is really years, it is not something I made up. All that time goes so our cars can go through those cones above in the best possible way, at the highest possible speed and with the least trained driver behind the wheel. Those are the real tasks that safe life. I am sure they know very, very well how to make the A4 Golf (for example) be a lot more “fun” to drive, with a lot less under steer, etc – but a Golf like that perhaps will fail the above tests so badly, in the hands of the untrained driver, and so the corporate decision is to go with plan “B” – a car which the enthusiasts will not love, but in which everyone is going to be safe, regardless of their driving skills, road conditions, etc. And when looking at those tests above, our A4s and A5s are actually top performers, so it is not quite true that they “suck” in handling – they can actually “handle” those situations very, very well and car like that can not be called a bad handling car.
 
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IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
Ceilidh, remember this saying (from Henry Manney at R&T, IIRC, "Hark the Herald axles swing"? Good thing we're not talking about camber compensators in VW bugs to keep the swing axles from jacking up. Now that was scary. Thanks for your post: at least I didn't run out and yank the Shine rear bar out of my wagon. I realize the TT spindles negative more positive camber as the car rolls, but they go postiive eventually. And the relationship between front and rear was, I think, what got the FWD TT in trouble.

Peter, I always buy Car and What Car when I'm traveling through Heathrow (can't read Italian) and the tests are so much more informative than ones in the US. And of course they get all the good cars, too. Maybe it's time to follow Dick Shine's advice, and leave everything alone and get better tires.
 

GoFaster

Moderator at Large
Joined
Jun 16, 1999
Location
Brampton, Ontario, Canada
TDI
2006 Jetta TDI
I wonder how the SUV's that Americans love buying would do in that elk test ... That test is not kind to vehicles with a high center of gravity and soft suspension tuning with inadequate damping. When the car first turns left, it loads up the suspension in that direction, and then when the car turns right, it has momentum acting in roll from the suspension unloading in addition to the steering forces.

I can see how the first test would be unkind to a Porsche 911 without all-wheel-drive and without stability management. I've seen someone spin one of those on a motorway off-ramp. I saw the brake lamps on as the car entered the corner fast, and I knew it was not going to be good. (Fortunately, he didn't hit anything, but no doubt learned that you do not do that in a rear engine car!)

Trailing-throttle oversteer is tough to get rid of. If I'm reading this correctly, you need rear suspension that keeps the wheels vertical or induces slight negative camber as the rear unloads. That's possible to do with upper and lower link suspensions (e.g. VW MkV, but also Ford Focus, Honda Civic, and several others). Beam axle has other problems but is actually not bad here, because it keeps the wheels straight up no matter what the body does. Pure trailing arm (e.g. original BMC Mini, many Renaults, early 80's Toyota Tercel) is OK for this, but not good in body roll. MacPherson goes in the wrong direction when the rear unloads. I do know that my first-generation Honda Civic from many years ago, which had MacPherson all around, had vicious lift-throttle oversteer. Perhaps good on road rallies, but not good for the ordinary driver. First time I spun mine on dry road was when I was 16, with a driver's license about 6 months old ... The spin happened on a corner which crested a hill, and I can see now how that compounded the wrong geometry induced by the lift-throttle situation.

Great thread, keep it coming.
 

mr.mindless

Veteran Member
Joined
Jan 23, 2006
Location
Rochester, NY
TDI
2002 Galactic Blue Jetta GLS
quite possibly the best thread I've ever read from an information standpoint.

I don't have much to add, but a bit - and a question.

I've had my MkIV for about 8,000 miles now, and I'm absolutely still learning about it. I have a Nuespeed RSB waiting to go in, and I have played with disconnecting my FSB which had some unexpected consequences.

First, the FSB disconnect. I honestly didn't notice the car rolling much more than stock. Cornering felt squishier, but more consistant becuase that outside tire had more weight on it. I've been wishing for a Quaiffe since I first cornered the car hard to get rid of inside tire spin when accelerating out of a hard, slow corner usually in 2nd gear, and pulling an end link of the FSB did just that which was very nice. I'm hoping that when I put in the 28mm Nuespeed that it will accomplish roughly the same effect by limiting overal roll and keeping that inside front loaded a bit more so I can put power down exiting corners.

Until I started reading this thread I didn't know about camber steer, that has made me much more sensitive to exactly what my front tires are doing when I corner hard and I understand a LOT more about why my car is doing what it's doing, and recognise tire grip more thuroughly which is a very useful thing to be able to read. I now also recognize that the Neon R/Ts I drove at Road America almost 7 years ago were behaving very similarly at-limit, though in a 3 day driving school they didn't get nearly this in-depth about why the car was doing what it was doing.

I've read in another thread about how GTDI's setup is working and I as I come to understand more about it and why it's doing what he describes, I still think that it is probably putting him in a very similar place to where I want to be.

If I ever get around to putting the Neuspeed on I'm going to play around with it with and without the FSB on an otherwise bone stock suspension and see what I can see, I think it will be interesting. I'm somewhere between Slow Car Fast and GT with more than a little rally-style driving creeping in, and I'm really just aiming for what feels the best and makes me smile the most while being entirely predictable, rather than just the fastest. The roads where I drive are both curvy and hilly and I don't want unpredictable tail swing when I crest a hill coming into a corner when I don't know if there's oncoming traffic.

Finding a slow-moving school bus on the far side of a hill on an otherwise empty road makes me want better brakes too, but that's off topic for this thread (the bus and I - and my brake pedal as well by a smaller margin - were fine, with plenty of room to spare but I'm sure I could have fried an egg on my brakes, they faded BADLY).

EDIT: and of course I forgot my question.

with the massive caster angle we have, how does that factor in on a slow, hard corner. Definitely more on a concern for autoX than GT or Slow Car Fast, but with the camber that introduces at lock, that's got to have a huge effect in hairpins. As I drive, to the point where I feel totally neutral through anything that's slow and >90°, but with the front sway hooked up I have hopeless inside front tire lift and have no hope of powering out quickly.

I'm improving my trail braking technique and it's having a massive impact on turn-in, holding and follow through with the bar hooked up again though....
 
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Golf_GTDI

Veteran Member
Joined
Jun 12, 2004
Location
Logan Ohio, USA
TDI
2001 Golf GLS
GTDI, please do tell us more! In particular, what are the situations that bring the tail around (i.e., what do you do to encourage it?)
To be honest I try not to encourage it too much. As of late however I think that I am getting a bit more comfortable with it. The other night Oliver came into town prior to us taking the rally car to the show in NC and one of the first things we did was jump in the car so I could show him what the car was doing. I have found it easiest to get the car to give this feedback when the rear gets a touch of lift (when cresating a small rise for instance). I think I felt it at higher speeds due to the slight rear to front weight shift when factored in with a slight roll from one side to the other. This has led me to wonder if the wing added to the TT was more than fluff, could it be that they wanted to keep the tail planted a bit better in just this situation?

Do you need to "toss" the car, or can you bring it out with a little throttle lift mid-corner? Can you drive through it with steady throttle and countersteer, or do you need to feed in more power?
Good question but I have to say that I've found it to be a bit of none of the above. The two things I'm doing are 1) avoid the situation by trying to get a bit of a preload on the front outside tire when getting into a curve. If I can load it up a touch the car will not suddenly buck and kick as if its trying to kill me. 2) If it does kick it happens so suddenly that its hard to do much of anything. I just make no sudden movments or overadjust and let the car settle.

When you say it happens at 65mph, can we assume that it would continue to happen at higher speeds, or do you mean there's a speed band in which it occurs?
You sure do know how to build to the big points don't you. I honestly don't know what happens at much higher speeds. While I tend to drive rather quickly I don't tend to turn hard enough to make this happen at 70+ mph on public roads as a matter of fact I don't try to turn much at all at those speeds. I will also admit that if I did have this car out on a track I would test this with some serious respect. I have honest fear that the car would kick so hard that it could come around and spin or even roll seeing as this is the feel it tends to give at that very moment.

I have not talked to Oliver much about what he felt and what his thoughts on the matter were much past the "thats what I'm talking about" bit while in the car but will be chatting with him about it sometime soon I hope.

I have however talked to Peter in regard to this about dampers in particular seeing as I am thinking that stiffer dampers will slow the rise and transition of the rear and help eliminate this problem. then again it could be more one of geometry and less of simple dynamic movment which would make for a whole other set of problems to fix.

Hope this helps a bit, if not drop me a note off topic and we can chat.

I would also say that after getting out of my car and getting into Olivers the feel is worlds apart. His car is very button down and reserved. Mine is more high strung with less feel and stability. I wish I could have taken the wheel and tires off his car and swaped them to mine for a bit but it is not to be at this point in time. New rubber will tell me a lot more soon.

I was also able to drive a new 2006 Civic and while my first few moments in the car were nice the long drive in it made me miss my own car. That civic may in fact be one of the most slow nosed cars I've ever driven. It almost felt in somesituations that it was pulling an ancor it was understeering so badly. If you pushed it hard however it actually seemed to feel a little lighter which was odd and the grip at the limits was good. Feedback was crap with the brakes giving no notion of what was going on where the rubber met the road. I think its a car that my mom would love and I'd put a 16 year old in but that car would try to suck my soul out if I drove it every day.
 

peter pyce

Veteran Member
Joined
Nov 6, 2001
GoFaster said:
I wonder how the SUV's that Americans love buying would do in that elk test ....
It will take some time for me to gather all the numbers as they are all in different magazines, so I have to go through them one by one, but here are some I got so far. This was a comparo among 11 SUV through the "Elk Test". Here is the way the got classified, but note how the ranking is not in order of the highest speed and I will explain later why:

1. Land Rover Discovery - 62.7 km/h
2. Porsche Cayenne - 59.3 km/h
3. BMW X5 - 58.9 km/h
4. VW Touareg - 61.4 km/h
5. Lexus RX 300 - 61.4 km/h
6. Nissan Murano - 59.8 km/h
7. Mistubishi Pajero Pinin - 60.0 km/h
8. Nissan Super Terrano - 58.8 km/h
9. Jeep Cherokee - 58.8 km/h
10. Volvo XC 90 - 58.5 km/h
11. Toyota Rav4 - 57.8 km/h

Now, as you can see, the Touareg (and Lexus) have the second best speed through the test, but only placed 4-th and 5-th (The Mistrubishi is in similar situation, performed well but placed behind). This because the ranking is based not only on the number, but also on the evaluation from the test driver. Basically, the car is capable to go with such high speed (comapred to the rest) but the tester felt that it takes extra skills for the final touch and in some cases the average driver may not be able to cope with what it takes to go at that speed through the test. For example, in one of the cars the ESP got little bit more brutal than the necessary, so the tester said "That could induce hesitation in the driver, which could lead to trouble", etc. So, that car performed well in the hands of the experienced tester, but they would place it lower on the list for the above mentioned reason.

To put these numbers in perspective, the Dacia Logan that rolled over from my previous post did so at 60.8 km/h and the New Mercedes Class A is (funny enough!) now one of the leaders in this test and goes through at about 65 km/h.

Another interesting thing is that the same magazine said (time ago) that the Jeep Cherokee actually rolled over during an American magazine test, doing simply 700 ft slalom (those tests that Car and Driver usually do, but they did not say the name of the magazine!), but the same car then performed pretty well (as you can see from the list above) in the Elk Test in Italy.

More data is I go through the magazines, but it will take me some time...
 

IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
I just spent the day getting some firsthand experience of VW suspension engineering, although in an A3. I did a track day today at the road course at New Hampshire International Speedway. What fun! I went in my A3 because it's closer to stock (good for classification) and, as I've posted before, I feel very comfortable in it. I have Neuspeed Sofsports, Koni Reds on full soft, and a Neuspeed 28mm rear bar on the middle setting.

First, I have to say that this TDI is a blast to drive fast. Second, remembering that I was put in a group with other novice drivers, I had no problems staying with the Miatas on the track, as well as one poorly driven BMW 330i. And there was more than one time I pointed an Evo or WRX to pass me but they couldn't. Diesel rocks!

Anyway, the car's handling could only be classified as 'can do no wrong.' even with the rear bar the transition to terminal understeer was progressive and totally predictable. Not once did the rear come around, even when braking in a corner (remember, I'm a novice). And the smoother I drove, the better the car responded.

Summary: VW engineers do know what they're doing. We should do our homework before second-guessing them.
 

dingchowping

Active member
Joined
Sep 27, 2004
Location
Seattle, WA
TDI
'05 Jetta GLS TDI
Hi Pyce and Ceilidh,

Wow...what a thread! I rarely read any type of forums as much of their content I find to be unsubstantiated noise. But this...this deserves more than just a sticky. A spot in the FAQ would begin to do justice to the value of this information!

Now to the point of my post: I thought you might be interested in another data point on the handling issues (or virtues, depending on how you look at it) of the original unrevised TT suspension setup. My mom drives an early production TT 180 quattro (9/99 production date) which still has the original suspension, no rear spoiler, and no ESP. I've had quite a bit of experience driving this car in a variety of conditions including street, autocross, and track in a variety of conditions (everything except snow).

A bit of background so you know where I'm coming from: I attended my first track event when I was 18, about 11 years ago, and I've been instructing for the local Audi club for about 8 years now. Our events include traditional track and driver training events, autocross, and if conditions permit winter/ice driving courses, so I feel I have a fair understanding of vehicle dynamics. Until recently I was also involved with one of the small tuning shops you mention in one of your posts. I had to laugh at your description which is startlingly accurate. But what you don't mention is that these shops are selling components manufactured by very well known, very well respected companies. Its not just the fault of the little guys, its the tuning industry in general. But that's an issue for another post.

My years spent turning wrenches at a speed shop gave me a unique opportunity to drive a wide variety of VAG products with countless combinations of suspension "upgrades." The more aftermarket setups I drove, the more impressed I was with stock setups, especially my mom's TT. My first drive in the car after she took delivery of it, my dad and I took it up to an empty parking lot on a rainy night to see what it would to. I expected typical Audi quattro handling...IE sluggish turn-in followed by massive understeer. What I got was reminiscent of a term I first heard coined by Hans Stuck, "sneeze factor." The driver sneezes and the car changes lanes. On top of that, when the front tires broke loose, the rears were right there too, causing a 4 wheel drift. Whoa...a BALANCED Audi quattro???

My next opportunity to really explore what this suspension could do was at our Quattrofest event at Portland International Raceway a few years ago. The TT was one of the slowest cars I've driven on the track in terms of sheer acceleration, but its fantastic handling made it one of the fastest cars around track, allowing me to lap S8s, M3s, S4s, etc. The car was at its best in the first 4 laps, after that the stock Bridgestone RE040s got rather hot and "greasy" feeling, necessitating more throttle input to keep the car pointed where I wanted it with the reduced traction. However, the TT's chasis was so communicative that figuring out what changes to my driving were necessary to deal with the reduced traction felt almost intuitive. It was, and today still ranks as the most fun car I've driven on the track. Even my freind's 450 hp 4000 quattro race car comes in second to my mom's lowely stock TT.

Later that summer the club put on an autocross. In this context the TT really shone, as I was vying for fastest time of the day, the other contender being my future business partner in a heavily modified 2000 S4. Toward the end of the day the event master and course designer, who is a VERY experienced autocrosser asked if he could give the TT a run at the course. I tossed him the key, but before his run he asked if it behaved like a typical Audi quattro. I told him it tends to be a bit more neutral, but I probably should have told him to treat it like a Camaro as he proceeded to knock over about 14 cones, all with the back end of the car in an impressive display of tire squeeling and tank slapping. Oops.

My first experience with the MKIV chasis was a '97 Audi A3 that was owned by one of my students at a track event about a year before my mom got her TT. The A3 had been imported by H&R as a demo car, so they pulled out all the stopps, installing TT spindles, coil-overs slammed to the ground, and their biggest bars front and rears. Talk about a darter! This thing did NOT want to go straight. The front straight at Bremmerton raceway is rather bumpy, and every bump the car hit the nose would dart one direction or another. The worst bumps were in the braking zone too, which made driving this car an exercise in frustration, and driving it smoothly nigh on impossible. In fact the car's handling was so bad and the driver had to allocate so much energy and concentration to fighting the steering wheel that it was interfering with the driver's ability to take instruction and learn something. The owner sold it after a year.

I guess what I'm trying to say with all these anecdotes is given the right context the TT spindles can be A Very Good Thing. However they should be treated with respect, and associated mods should be done very carefully, otherwise you'll end up ruining what was once a very nice car.

I'm sure there are many, many people reading this thread (I among them) who wait with baited breath to hear what you have to say next, but todays post from IndigoBlueWagon brings up a very salient point. The single best way to improve the handling of these cars, or any car for that matter is not better tires, and it certainly isn't upgraded suspension, but rather improving the nut behind the wheel. Get thee to a driver training event and be blown away by how much you learn! I've been attending these events for 11 years, instructing at them for 8, yet I still learn a ton every time I attend one.

BTW, completely off the topic but I'm curious...Ceilidh is it safe to assume you have a Linn audio system in your living room? If you do, good on 'ya mate!

TTFN,
Adam
 

Ceilidh

Member
Joined
Mar 12, 2006
dingchowping said:
......BTW, completely off the topic but I'm curious...Ceilidh is it safe to assume you have a Linn audio system in your living room? If you do, good on 'ya mate!

TTFN,
Adam
(Sorry for the incredibly short, non-car post (I need time to digest the excellent recent posts!), but......)

How in the world did you know I have a Linn system in my living room????! It's a Classik + Ninka combo-- but how did you know that? :)

Hope to post later this week; all best til then!

- Ceilidh
 
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peter pyce

Veteran Member
Joined
Nov 6, 2001
Adam, thanks for coming in! We have tried (and failed!) to find someone with an early TT who also knew the newer TT's and who also knew what he is talking about and who also knew how to write in details - and here you are, all in one! Please, please, on behalf of me and Winston and everybody else who's interested - do try to find some time and sit down and give us as much details as you can on that early model TT. Especially if you can do a parallel comparison with other VAG products, and even more, if you can compare it to a later, post-recall TT. I never had the chance to find one and to drive it, but reading about you and your background, I am sure your words will be enough to understand in depth what was the car's character and how did behave in the most possible to describe scenarios. Take your time, please, no rush, but we will be waiting (patiently, we try) for your in dept coments. Thanks in advance!

DPM - I know they tested the Grand Vitara, just can't recall the issue, but will keep digging, so eventually will find it.

To everybody else who posted above - I do understand some of you are expecting answers to their questions, but this weekend is really dedicated to something else, so please be patient, it will all come next week.
 
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dingchowping

Active member
Joined
Sep 27, 2004
Location
Seattle, WA
TDI
'05 Jetta GLS TDI
Ceilidh said:
(Sorry for the incredibly short, non-car post (I need time to digest the excellent recent posts!), but......)

How in the world did you know I have a Linn system in my living room????! It's a Classik + Ninka combo-- but how did you know that? :)

Hope to post later this week; all best til then!

- Ceilidh
Hehehe...apparently it was just a very, very lucky guess. In the '90s Linn made a speaker called the Keilidh. My first exposure to Linn electronics was an Aktiv Keilidh system and I've been a Linn fan ever since. I just assumed by your sn that you had a pair of Keilidhs. I could also assume you're either Schottish, like parties, or both. But you know what they say about the word assume...;-)

TTFN,
Adam
 
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