What is Handling?

dingchowping

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Sep 27, 2004
Location
Seattle, WA
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'05 Jetta GLS TDI
peter pyce said:
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.
Hi Peter,

I'm glad I could be of help. I'll try to post more later today or tomorrow but I've driven I'd guess around 100 TTs in various states of tune, so I need to organize my thoughts into something less resembling word vomit before I post. I'll get back to 'ya soon.

TTFN,
Adam
 

peter pyce

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Joined
Nov 6, 2001
mr.mindless said:
.....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........
As you observe correctly, we have pretty good amount of caster on our cars (around and between 7 and 8 degrees, it depends how low you are). That makes for an artificial camber, which comes only when the wheel is cranked in one direction or the other, and the more it is cranked, the more the camber. Here is an animation that show pretty well what is going on an A4 VW, how the camber changes with steering input due to the caster:

(note: this is the front left tire, and you are looking at the car like if you were standing in front of the car, looking back towards the car)



It is pretty visible how great the negative camber gets if the wheel is the outer in the curve and how great the positive camber gets if the wheel is the outer in the curve. Here is a graph that shows these values, so some comparison could be made between different degrees of steering input:



(note: this is degree of steering at the wheel, not steering wheel degree!)

We gain about -0,7 degree of camber in the 5 degree steering, then we gain another -0,5 degree for the next 5 degree and so on. Due to the geometry, the gain is digressive, but it is plenty and at certain point exceeds the rear, which does not change during steering inputs (ok, it changes little bit due to body movement with steering, but it is so small, we will ignore it).

So, what happens when we drive in a fast, long curve? We get less steering input, so less camber gain and as we go fast, we get into under steer (pretty well explained by Ceilidh so far) due to the front losing camber faster than the rear, etc… (let’s do not go over again). Next thing we do is panic, and with the panic the instinct kicks in, we do two major things:

1. lift and perhaps even brake and
2. steer even more as to keep the car in our line and keep it on the road.

So, the #1 was explained very well, it transfers weight to the front, so loads the front tires more, they to grip better and that helps to pull the car “in” the curve, etc. At the same time #2 is where the big caster makes it so we gain greater negative camber the more we steer into the curve, so #2 helps even further as now we have loaded front tires from #1 and also we give more negative camber to those same now loaded more tires, which makes them grip even more, so the net result is that the front grips again, the understeer is interrupted, the front “comes back” and we “save” the situation without even being trained drivers – all we did is follow our instincts.

As also explained by Ceilidh in earlier posts, the sharper the turn, the more the understeer (even with low speeds) on our cars, so the more negative camber we need on sharper turns, which is something the caster gives us. The reason your front inner tire spins in powering out of the turns is mainly due to the whole concept behind the setting for this car. It is basically ”built-in” stuff, a compromise if you wish to call it, as other things are/were more important than the power-out of a curve. Simple things like removing the front bar/going stiffer in the rear/resetting dampers, etc will cure that, but will of course bring other issues to the table. A car modified like that will not be as good for the masses, so you have to personalize it some if you want it to do few more tricks.
 

Davin

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L.A.
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2001 Golf GLS 5spd blk/blk
Why did I wait so long to read this thread? Charts, animations, numbers, oh my! Even mention of matlab/simulink modeling! All it lacks now are some equations... but those can get pretty complex.

Reminds me of one of the questions I had during my dynamics/vibrations qual oral exam. I was asked to derive the ground force caused by a simple one-wheel-on-a-spring suspension model travelling over a sinusoidal roadbed. I was then asked if the equation I came up with would always be valid. My response was... not if the wheel comes off the ground!

nate... did you model the vehicle in full 6-dof or did you only look at rotation? and did you have realistic models of the suspension geometry? did you calculate the EOMs by hand or did you use a package?
 

peter pyce

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Joined
Nov 6, 2001
Just a quickie on tires….

We have been talking for quite some time how tires are the best (and most of the time – the only!) real performance enhancer when it comes to speed in curves, road holding, grip, etc. So, I ran across an interesting article on the new FIAT Panda. The car was also put under the “Elk Test” and there is something interesting that happened. The basic model had some sort of ordinary tires (all season) and performed quite well actually (for such small car, pretty tall too). Then they tested the upper tier model, which was basically the same car (suspension wise) but had performance tires, which is a trick many car companies do – just put bigger wheel and sticky tires on their “sport package” and that is it. Anyway, due to the stickier tires, not the car has actually issues in the Elk Test as it started to lift BOTH inner wheels (!) It did not roll over, but perhaps because experienced driver were behind the wheel and knew how to take care of that, but guess what could happen if the average Giovanni drives the car? Here is a pix that supports the story (The Panda on two wheels from the test):



Then there was another interesting piece, on a Honda Minivan, where they tested both the basic model and the high tier model together. They both had all season tires, the exact same brand and model, but the basic model had them H rated and the high tier model had them V rated. The basic H model did very well in the lift-throttle and change lane test (the one we were talking earlier in this thread) and went through at speed of 102 km/h. The V rate tire model, thought, barely passed at only 100 km/h and the tester was commenting that due to the soft suspension and specific geometry on such vehicle, the car rolls a lot more (it is a minivan!) and at that point the softer tire wall H rated tires actually help a lot more (work a lot better) than the stiffer side wall V rated tires, therefore the higher tier car could not go as fast as the lower tier counterpart.

P.S: By the way, if a vehicle lifts both inner wheels during the Elk Test, it is considered a failure, even if the car does not roll over.

.
 

cartog

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This is quite interesting. I wonder if it relates at all to the earlier reminiscence for old English sports cars with slippery tires. Could slightly less grip help the rear come about a bit better?
 

Slave2school

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Angus, Ontario
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99.5 used to at least...
Yes when the tires are leaned inward towar the centre of the car it is negative camber. I guess the funciton is that when the car is in a corner more of the tire is flat with the road.

With even wider tires it gets more exagerated and easier to see, this is a shot from my car.



I hope that helped a bit, this is all pretty new to me too.
 

frugality

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Spring Lake, Michigan
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none, 2016 GTI
peter pyce said:
Then there was another interesting piece, on a Honda Minivan, where they tested both the basic model and the high tier model together. They both had all season tires, the exact same brand and model, but the basic model had them H rated and the high tier model had them V rated. The basic H model did very well in the lift-throttle and change lane test (the one we were talking earlier in this thread) and went through at speed of 102 km/h. The V rate tire model, thought, barely passed at only 100 km/h and the tester was commenting that due to the soft suspension and specific geometry on such vehicle, the car rolls a lot more (it is a minivan!) and at that point the softer tire wall H rated tires actually help a lot more (work a lot better) than the stiffer side wall V rated tires, therefore the higher tier car could not go as fast as the lower tier counterpart.
That's very interesting. We've had a good number of threads on replacement tires here, and there has been some head-butting over whether it's O.K. to use lower-speed-rated tires or not. Often someone will say, "Even though you may not see the speeds that an 'H' rated tire is capable of, that tire will perform better overall and be safer because of the stiffer sidewall." This information seems to question whether the stiffer sidewall is necessarily safer.
 

Doc_Oc

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frugality said:
That's very interesting. We've had a good number of threads on replacement tires here, and there has been some head-butting over whether it's O.K. to use lower-speed-rated tires or not. Often someone will say, "Even though you may not see the speeds that an 'H' rated tire is capable of, that tire will perform better overall and be safer because of the stiffer sidewall." This information seems to question whether the stiffer sidewall is necessarily safer.
But what applies to Honda Minivan...does not apply to MKIV Golf or Jetta. Or maybe it does.
Across multiple thread I read things like, better tires is what you need, not better shocks. Others are saying exactly the oposite. I think the tires have as important of a role as the springs, or the dampners. They all work together or they don't work at all. Well...they do, but the handling sucks.:confused:
What would realy lighten everything up would be The Elk test on a Golf with stock tires vs stiffer tires, or even bigger rims (17") with performance tires. Let's hope Peter will find something about that.
 

Nate_Grauvogel

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CO
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Davin said:
Why did I wait so long to read this thread? Charts, animations, numbers, oh my! Even mention of matlab/simulink modeling! All it lacks now are some equations... but those can get pretty complex.

Reminds me of one of the questions I had during my dynamics/vibrations qual oral exam. I was asked to derive the ground force caused by a simple one-wheel-on-a-spring suspension model travelling over a sinusoidal roadbed. I was then asked if the equation I came up with would always be valid. My response was... not if the wheel comes off the ground!

nate... did you model the vehicle in full 6-dof or did you only look at rotation? and did you have realistic models of the suspension geometry? did you calculate the EOMs by hand or did you use a package?
Quick reply here: Yes, we did it the hard way.

Everything by hand (I said it took a semester!), 6-DOF, and relatively realistic suspension geometry, limited by the data we had on the car (no bump steer if I remember right - didn't know the inner tie rod location)... but I believe the tire model was the limiting factor in regards to suspension. (neglected changing camber)

Off to bed now... still an awesome thread.
 

Golf_GTDI

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Logan Ohio, USA
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I say we set up some tests to run at a GTG or maybe TDI fest this year. Let folks with all sorts of cars with all sorts of tires do some simple tests to see what happens. The driver may be an issue but then again we could have Jon or someone wheel many of the cars to keep things even from test subject to test subject.

The other day I got my car rather tail happy and had to wonder how much if any of it had to do with tires. I was stunned that the rear broke loose and did so rather easily at the speed I was going.
 

mr.mindless

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Golf_GTDI said:
I say we set up some tests to run at a GTG or maybe TDI fest this year.
That would be extremely valuable. cars everywhere from mine (bone stock suspension) to yours (just plain sweet), and we can play around with some of them pretty easilly (swapping swaybar settings on Neuspeed bars, disconnecting fronts, etc) and do some tire swapping and see what lands where.

I'm absolutely in, I wouldn't mind anything within 4 hours of here and that would probably just about get me to you (Cleveland is about 4 hours from me), further is fine if I can crash someplace. The Jet is a damn small car to sleep in :)

So what would be the best test(s)? As we've established, AutoX is definitely a different beast than GT and I think those of us with the most interest are more of the GT/Slow Car Fast leanings, but it's certainly the easiest thing to quantify with a stopwatch.... We could do elk test/chicane/slalom something... Other ideas?

Would be great to get a trustworthy group together so we could see how each other's cars felt and what we like/dislike too. Not sure how others might feel about that. Hell, not sure how I'd feel about that :) Just another thought.

This may deserve a different thread so we don't pollute the good tech in here planning a GTG. If there are a couple more people who think this is a good idea (whether in OH/PA/NY or elsewhere) let's start a new thread and move these posts there. We do get to delete our own posts on this board, right? [yes we do]

EDIT: okay, get me halfway there... I was actually remembering another guy on the board's location, "NE Ohio", Logan is about 8 hours from me. Would definitely rather meet in the middle than go all the way there, then, but we'll see if anyone else is even interested and where they're located. maybe get the other RallyVWers and the rally car involved to, that'll get me there just about any time :)
 
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Ceilidh

Member
Joined
Mar 12, 2006
tires and handling balance

cartog said:
This is quite interesting. I wonder if it relates at all to the earlier reminiscence for old English sports cars with slippery tires. Could slightly less grip help the rear come about a bit better?
Hello cartog,

There are actually (at least) three somewhat independent phenomena going on here:

1) One concerns the Honda minivan:

.....Then there was another interesting piece, on a Honda Minivan, where they tested both the basic model and the high tier model together. They both had all season tires, the exact same brand and model, but the basic model had them H rated and the high tier model had them V rated. The basic H model did very well in the lift-throttle and change lane test (the one we were talking earlier in this thread) and went through at speed of 102 km/h. The V rate tire model, thought, barely passed at only 100 km/h and the tester was commenting that due to the soft suspension and specific geometry on such vehicle, the car rolls a lot more (it is a minivan!) and at that point the softer tire wall H rated tires actually help a lot more (work a lot better) than the stiffer side wall V rated tires, therefore the higher tier car could not go as fast as the lower tier counterpart.


I'm not familiar with this minivan, nor do I know the specifics of how its particular test went, but from Peter's quote it sounds like the V-shod minivan simply had less grip and agility than did the version with H-rated tires. Surprisingly, this sort of reduction can sometimes happen: different tires respond to camber in different ways, and some (A) have more camber thrust and others, and/or (B) have more loss-of-ultimate-grip due to camber. In general (though with tires, there are exceptions to almost any rule of thumb!) a stiff-walled tire tends to generate more camber thrust, so if you lean it away from a corner (as seems to be happening with the Honda), it'll steer away from it as well; and with stiffer walls, you also have more likelihood of lifting the inside portion of the tread off the road, thereby reducing your ultimate grip.

As an aside, these effects can also apply to low-profile tires: in general (again with exceptions!), the wider and lower a tire's aspect ratio, the less the tire enjoys being cambered adversely in a corner. For some -- perhaps even many -- innocent little FWD cars that get tarted up with big-wheeled "performance" packages, the cars would actually grip better if shod with taller, narrower versions of the superwide rubber that comes with these packages. Of course if you did that, people wouldn't buy the packages! (The marketers have done a good job convincing everyone that wider is better..) And if you make sure that you spec your option list such that the choice is between a narrow all-season versus a wide high-performance tire (i.e., nobody actually ever compares a narrow versus wide performance tire), the big performance tire will in fact grip better than does the narrow all-season (simply because of the rubber tread compound), so no one is ever the wiser.

In any case, suspensions that are designed for stiff and/or low-aspect-ratio tires usually keep the tires a bit more upright in a corner, either via suspension geometry, or by reducing overall roll. If you don't do this, and you continue to let the car roll, you often don't gain much from the stiffer/lower tire, and sometimes you actually lose...

2) The second one is tricky, and we won't get much into it here....

Then they tested the upper tier model, which was basically the same car (suspension wise) but had performance tires, which is a trick many car companies do – just put bigger wheel and sticky tires on their “sport package” and that is it. Anyway, due to the stickier tires, not the car has actually issues in the Elk Test as it started to lift BOTH inner wheels (!)
....but what MIGHT be happening to the Fiat Panda referred to above is the sort of dynamic instability alluded to by Nate several weeks ago. That is, the Panda might be rocking up onto two wheels simply because it now has better grip and is cornering faster (and thus generating more g-forces), but it wouldn't be surprising if a more subtle phenomenon is also at work here.

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... __________________
Nate
I'm not sure we'll ever get time to discuss this issue very much (this thread seems to have taken on a life of its own, with multiple subthreads going every which way!), but the resonance effect Nate refers to above is quite real, to the extent that -- if you believe rumors -- almost any car can be rolled if steered in just the right way at just the right speed...

(sigh) :)

Ok, I'd better explain a little bit right now! :

For the young whippersnappers in the audience who have no idea how the Mercedes A-class enters into this discussion: the famous-in-Europe Elk Test was just an obscure handling test performed by a more or less obscure Scandinavian motoring journal (I'm sure the Swedes & Norwegians et al read this journal, but hardly anyone else did back then!), until the day that a revolutionary, long-awaited, much ballyhooed Mercedes shocked everyone by rolling over in the middle of it. This was the A-class, and before that fateful day, Mercedes had poured millions and millions of dollars (deutsche marks back then...) into advertising how it was a safer, better-handling, more-comfortable, roomier, higher-quality, and simply better-engineered small car than had ever existed before. The advertising runup took literally months and years, and in Europe (where smaller cars are king) there was a lot of anticipation for this radical vehicle (the A-class' architecture is very unusual and clever) from the world's exemplar of engineering prowess. So the last thing anyone expected was for the Mercedes to roll in a test that more mundane cars routinely pass, and photos of the Scandinavian test driver being carted into an ambulance, with the partially destroyed Merc lying sideways in the background, were about the worst thing marketing-wise that could have happened to the folks in Stuttgart.

There were a lot of reasons why the A-class rolled, but much of it comes back to what Nate brought up: there's a certain resonance in a vehicle's handling, and the Elk Test happened to hit it on the A-class. Until that day, Mercedes never ran its cars through that particular test (it's been argued that it's quite contrived, and real people don't actually respond to an obstruction in quite that way), and thus didn't know of the problem; and hence they got very, very unlucky.

Where is this leading? Well, back to the rumors: one of the many interesting things about the whole A-class debacle was that absolutely nobody -- not a single European, Asian, or American car manufacturer -- ever came out and said anything evenly remotely critical of Mercedes or of the A-class. Not a single cheeky advert boasted that "Our cars stay planted!"; not a single press release referred to "Our engineers perform a battery of tests, to ensure that no handling surprises will catch anyone out..."; not a single commercial talked about "our cars' wide stance and stability, which keeps our cars upright where competitors fail....". If anything, an occasional competing exec would say something like (when interviewed and essentially forced to say something): "Well, Mercedes is a fine company, and I'm sure that they'll sort everything out...". So what was going on here?

Rumor has it that the reason that nobody took advantage of Mercedes' predicament was that everyone knew it could easily have happened to them. A few engineers murmured something to the effect that "...mumble...mumble...well all cars can roll if you do the right th.....mumble...mumble" before being silenced by their respective companies and having their quotes expunged from the records. And then there was a very strange rumor that shortly after the Elk Test disaster occurred, Mercedes bought an assortment of cars, trucks, vans, and hatchbacks from all its competitors, and instructed its presumably-exceptionally-highly-paid test drivers to find a way to roll each and every one of them in front of the video cameras, with the resulting footage going into a Mercedes vault somewhere, with word sent out to the various competitors that they might not wish to capitalize on Mercedes' predicament.

Interesting, non?

In any case, going back to the Fiat Panda on 2 wheels: as Nate says, there's a particular frequency where cars begin to go unstable. And when you change the tires, you change the response rate to steering motions, and sometimes -- if you're lucky/unlucky -- that's enough to nudge a car towards instability in a particular test. So it's possible with the Panda that the 2-wheel result is not just from the tires being stickier, but also from their being more responsive.


3) And finally (though I'm going to have to pick this up in a future week, as I'm out of time)...

cartog said:
This is quite interesting. I wonder if it relates at all to the earlier reminiscence for old English sports cars with slippery tires. Could slightly less grip help the rear come about a bit better?
On many cars, less overall tire grip can lead to reduced understeer (especially with the old English sports cars!!) -- but we'll explain that some other day.

Cheerio lads!

- Ceilidh
 
Joined
Apr 11, 2006
Location
Berkeley, CA
Rear bar only comments

Quote: " We'll talk about the big-rear-bar/ soft front setups more in a later installment, but ...
a big rear bar will only reduce the initial amount of roll. At some point, the inside rear wheel will lift ..., and when that happens, it really doesn't matter whether there's a big anti-roll bar in the back or not: as far as the car is concerned, there is one wheel on the ground in the back, and two wheels on stock springs and stock bar in the front. Hence at the dry-road 3-wheel cornering limit, a big-rear-bar car will understeer about as much as will a completely stock car ... Now, this is a fairly horrible handling set up (understeer sets in rapidly the moment the rear wheel leaves the ground), but there's no oversteer at the limit....
And for this someone has paid $300?"[/quote]


Oh, such a great thread! So much to comment on!! So many sidetracks I want to follow! Thank you guys. Pyce and Ceilidh make a great team. ...I pick one sidetrack:

The discussion hasn't got here yet, but for when it does.....I must comment on this rear bar discussion above from (Sir) Ceilidh (looks like I didn't do the cut/paste quote properly).

I currently have a big rear bar with otherwise stock (GTI, yes another guest gassie, tho I love TDI's) suspension, and it is an interesting set-up for me, mainly a GT man presently...

Big big turn-in improvement, big big reduction in understeer up to around 8/10's? (where I spend 98+% of my time), and still safe at the limit. Yes, wonky body motions over big bumps and yumps. Certainly not 'horrible' tho, and some of the best $300 I've ever spent.

Yes the inner rear tire lifts sooner. No this does Not mean sudden balance change. Really the transition is nearly invisible (to me at least, very high rally gravel/snow skill but light on serious tarmac experience).

At increasing cornering loads, the inner rear tire load decreases and its lateral grip decreases steadily (while outer increases). Inner tire load and lateral grip are near zero just before tire leaves the road. There's no sudden loss of lateral grip at that point, not at all. The inner wheel was already doing next to nothing by then. Its progressive as always.

Once the inner is off the ground, the big bar's effect is increased spring rate at the remaining outer rear tire = less bump/jounce, more remaining suspension travel, better able to deal with bumps. It still understeers at the limit = Safe. And believe me, I have tried everything to provoke this thing to get the rear to truly break, and it is very very hard to do so on pavement, even in the wet. That is, it's SAFE.

Unlike, apparently, with TT spindles as Golf GTDI reports. As a rally guy, I'm very comfortable with rear end movement -- I lived for it for years, reverse-flicking and left-foot-braking to bring the rear around. So I was planning to do the TT spindle swap next, but now look forward to more input here, particularly from the fellow with all the TT experience. I want a looser car, but then my wife loves me and would like to keep me around, so I need more info about the limit effects of the spindles.

Just some thoughts. Thanks all. Keep it coming.
 
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peter pyce

Veteran Member
Joined
Nov 6, 2001
Wishbone - it is very important to specify what kind of rear bar we are talking about! There are mild bars, which do exactly as described by you and there are very stiff rear bars, which make the car behave in a quite different way in all the set scenarios. I suspect you have sort of a "mild" bar, and if that is the case it must be specified, so the general feeling in whoever reads and have no experience such as yours may not just plain assume that rear bars is plain safe, because someone said so on the internet.....

Which brings another point it is time to make right now (great you talked in your post about yourself a bit!). The point is this: we are all at different levels when it comes to driving skills. From the words you put I gather you are experienced driver and that means a lot. That means you are well trained (you have it built-in into your instincts) how to drive a car fast, how to control a car that wants to "go", how to correct, how to "bring back", etc. A driver like your would have very hard time to fall into "unsafe" situation with a stock car, because you would simply know what to do way before the situation arises, and even if the scenario is really from the "panic" type, you would know (instinct) how to put the car where you want, how to avoid the danger, how to come out of all this without even making a note that it was one hell of a situation. So, for someone like you it is very easy to come in and say "rear bar is SAFE, I have one and it only helps me put the car where I want and so far I never had a problem". All that could be so true and perfectly correct to say, but so wrong if the reader of your post is very novice driver who has no idea what even what a rear bar does to a car. The goal is to help folks have a minimum understanding of what does what, how things work together and then make a more educated choice of what they need/want. You must be a good driver if you have no issues with your rear bar, but I have seen people spinning around on on-ramps, or in the mountains. Rear bar is safe in the hands of the experience driver, like the more powerful car is also safe in the hands of the experienced driver. Good night.
 
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Apr 11, 2006
Location
Berkeley, CA
rear bar alone - cautions

Hello! Yes I agree that caution is needed to keep from misleading people. I'm a mech engineer too and understand the need to take care with regard to all the possible users out there. This is why I explained that I have some driving experience. You are right to raise flags of caution here. My primary points were that there is no sudden change when the inner rear tire lifts, and that limit understeer is a good safe thing, with my current set-up.

Here is my set-up: stock 'sport' GTI suspension (including stock front bar of course), good 225/45-17 tires (fresh GY F1 GSD3, excellent in wet especially), H&R 28mm rear bar on 'maximum' hole, heavy gas-guzzling VR6 out front encouraging understeer.

So it is indeed a big rear bar. This is why after adding the bar I purposely went out to provoke and toss it to see if it would be scary in extreme situations. And as I report, I haven't found it to be so. Yes, into tight corners on the brakes, the rear end is light and will step out a bit. But this is in very aggressive driving and is easily controllable.... If you have some prior experience with this stuff!! as you say. But certainly in lower grip conditions (even just in the wet with less effective tires, but especially on dirt or snow!!), different more dramatic results could be seen. Any modded car should be approached with caution at first, preferably on a track at a lapping day. And the first mod investment should always be in the driver - in a school! Thanks for having me clarify.

BTW - Another Safety Sidebar - my H&R external rear bar came with pathetic clamps for attachment to the twist beam. I had three suffer fatigue failure - not good. I have now installed the better Neuspeed clamps with my H&R bar, as many others are doing. If you have or may buy an H&R rear bar, PLEASE see: http://forums.vwvortex.com/zerothread?id=2388065

Attn SF Bay Area people: there's a rally school coming up at Thunderhill. See http://www.sfrscca.org/RallyX/

Cheers, Pete
 
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Golf_GTDI

Veteran Member
Joined
Jun 12, 2004
Location
Logan Ohio, USA
TDI
2001 Golf GLS
If I recall the HR bar on max is still much much lighter than the street version of the Shine bar. I can not recall the exact numbers but I'll try and wander over and see if I can find the details later.

One thing I was pondering today and hope to see some feedback on is what makes a car fast from point A to point B. We all read tests and want to see what sort of numbers a car can make as far as G's or slalom speed but the cars that do best with these numbers are not always the fastest at track days nor are they the ones who get the raves from drivers as the best cars to drive fast.

In talking with Peter about issues for the rally car we both agree that maybe the fastest car is not always the fastest in a given situation. the driver of the car may not feel as comfortable with a car that is actually more capable and in the end not drive it as fast as a car that does not have as much ability.

I look forward to seeing more thought on other issues that add up to the final product. Steering, brake bias, traction control and a whole host of other issues that in the end make a car a joy or a task to deal with.
 

peter pyce

Veteran Member
Joined
Nov 6, 2001
Golf_GTDI said:
.....One thing I was pondering today and hope to see some feedback on is what makes a car fast from point A to point B. We all read tests and want to see what sort of numbers a car can make as far as G's or slalom speed but the cars that do best with these numbers are not always the fastest at track days nor are they the ones who get the raves from drivers as the best cars to drive fast......
This so much reminds me of my favorite thread ever! (Too bad the data was not really what people wanted to see/read/hear so it did not get so popular. Funny how most of the time folks say they want the truth, but when the truth comes out, it somehow no one wants to accept it as it is not as comfortable as they thought it would be). So, here is a copy-paste from that thread, basically bringing the essential for you. I spent a full weekend back then to gather this data and it was one of the best wasted weekends as it made me reflect so much on aftermarket parts and on your question in the quotes above – what really makes a car fast, what really works. Here is the original post from back then, unmodified:

….. We always wanted to see the "Big Test" happen, so to know once and forever which suspension is the best, which tires are the best, which anti-roll bar is the best, etc. I have been thinking myself about possible scenarios, so this big test could happen, but it is not going to be easy if we want to do it in a professional way, so for everyone to accept the results. Apart from the fact that if we do it right, it will cost a lot, etc ...... Then I was looking at the Tire Rack the other day and basically it came out that they have already done all the work for us! All we need to do is gather and evaluate the data. I do not even think we could do it better than them, as they use the same vehicles (Lexus IS300 and BMW 32X), and most of all on the same track, same day, same drivers, so the results from each test are pretty darn good if we are interested in the delta. Of course, those are not results with VWs, but the goal here is to have an idea about what gives what, and most of all to try to somehow quantify the different parts we al spend so much money on.

Let's start with the tires. Almost everyone here would agree that the best upgrade for our cars is tires. But the question is, by how much an expansive max. performance tire will be better than the "crappy" stock tire that I already have? The Tire Rack has done pages of comparisons, in all categories, but I think this one is kind of one of the most interesting and wraps it pretty well. They tested the Good Year RS-A in 205-50-17 (they use this as "base tire" so to be able to have starting and common point for majority of the tests) against three of the most popular Max. Performance tires, in 225-45-17, so those are wider tires as well! Here are the results from their web site:



Looking at the times, it comes out that the difference between the known Good Year RS-A (OEM on some VWs as well, and pretty much well known as"crappy tire"on these boards) and the best performer from every test is as follows:

- About 3.7% difference in the Dry Slalom (time wise).
- About 5% difference in the Wet Slalom (time wise).
- About 3.6% difference in Lap Times (dry)
- About 6% difference in Lap Times (wet)

Funny, isn't it? We upgrade tires and we feel that we can go twice as fast, but turns out is not the case :D Keep in mind that the Max. Perf. tires in this test were also wider (225 vs. 205) than the "crappy" OE tire!

Springs next..... They have done a comparo between OE Sport Springs, then Eibach Pro-Kit and H&R Sports on the same BMW328i. Lap Times difference between the slowest (OE) and fastest (H&R Sport) is an "amazing" 1.8% (!) :D Now, we know that on our cars the situation may be slightly different as we have little bit different geometry that does not react too well on lowering, so who knows, the OE in our case may even come out as a winner,you never know. But even if the OE "loses", the 1.8% difference in lap times is really less that what many of us thought an aftermarket suspension of this caliper would offer....... Here is a link to the full test. For the results go directly at the end of the page:

http://www.tirerack.com/suspen...d.jsp

Now.... Dampers! This one is even more incredible. =) They equipped three equal cars with equal tires, one with OE dampers (Lexus IS300), one with Koni Sport on full soft and one with Koni Sport on full stiff. Here are the Slalom and Lap Times:





- About 1.6% difference between OE and Koni Soft. (Slalom times)
- About 0.8% difference between Koni Soft and Stiff (Slalom times)
- About 1.3% difference between OE and Koni Soft (Lap Times)
- About 0.4% difference between Koni Soft and Stiff (Lap Times)

Who would have thought? When we drive it feels that the difference between soft and stiff is much more than those 0.4% :D

Next two are about aftermarket spring and then anti-roll bars too. The numbers look more or less the same, here are the links. Scroll down for the data:

http://www.tirerack.com/suspen...1.jsp

………

So, dear Daniel, looks like the tires do really the trick, and by far, and the rest are perhaps just confidence inspiring parts, which YES do help some in lap times, but it is not any near what we all have been thinking/feeling, etc. Now of course someone may come and say that on a race even 0,01 sec matters and that is sometimes the difference between the winner and the loser. That is so, so true, but I would like to make an important note here – we are talking purely street as all these gizmos tested above are sold to folks who drive their cars on the street and who expect to improve their cars on the street, and my point is that 1% of improvement in real life gains on the street is simply pathetic, especially if you consider the money spent and even more – if you consider the possible safety reduction of your new setup! Yes, safety! We have all driven lowered cars, cars with bars, stiff rides, etc and we could all swear that such cars are more stable and would be safer in emergency situation, but I am not quite so sure. When they do the Elk Test and the Lift Throttle in a Corner Test on cars with modified suspension by the aftermarket suppliers, then we will only know how those things really work in real life safety scenario. But I am guessing no one will dare to do such test and publish the data….

But let’s keep going with the funny data. There are two more things I would like to bring in here from another two threads that again did not get so popular, but it is real life data published there, so it is what we would like to work with when possible. For the following, data from “Road & Track” was used, so it is pretty reliable source right here in America. I spent some time to go through their slalom tests and put the data together, so to compare the tested by them Jetta V6 GLX Wagon and Beetle Turbo S. (By now they have tested few more models, but this info is from 2004, so let’s stick with those two cars. It was a thread with the title of “Slalom Speed – Why are we (Mk IV) doing better?”. It was inspired by the fact that if we look at the numbers given by these tests (7 cones, each at 100 feet apart, so it is 3 left and 3 right turns as fast as possible) – our bone stock VWs do not look bad at all in comparison to some cars that “should” be a lot better or at least we have always heard they are a lot better. So, here are the numbers we put together:

700 ft Salom Speeds (by Road & Track):

NB 1.8T Sport - 64.5 mph
Jetta VR6 GLX Wagon - 64.0 mph



These above are the numbers “our” VWs generated, both on All Season tires.

Here is a list of some well known cars that do equal or worse than out two VWs above:


Audi 3.0 A4 Quattro …………………… 64.1
BMW Z8 …………………………………...... 62.3
Chevrolet Corvette 50th Anni ….. 62.4
Ford SVT Mustang Cobra ………….. 63.5
Lexus IE 300 …………………………...… 64.5
Maserati Coupe Cambiocorsa ….. 64.7
Mazda MX-5 Miata LS ………………… 62.7
Mercedes C32 AMG …………………... 64.0
Mercedes CLK 55 AMG …………….… 62.8
Mercedes E 55 AMG ……………….….. 64.5
Subaru Impreza WRX ……………..…. 62.8
Toyota Celica GT-S …………………..… 63.6
Toyota MR2 ……………………………..... 62.6


I suspect (do not have hard data to prove it) that all of the above vehicles come to the marked (therefore, as tested) with tires that are “better” than the tires we get when purchasing Jetta GLX Wagon VR6.

You want to know the “champs”? Here are the Best:

Ferrari Enzo ……………………………........ 73.0
Porsche Boxter S ……………………....... 71.6
Saleen S7 ...................................... 70.6
Mini Cooper S …………………………......... 69.5


Also, according to the magazine’s test:

Mitsubishi Lancer Evolution 2003 ……. 68.9
Subaru Impreza WRX STI ……………...... 68.4


If we can trust this data, our cars do not look any near as bad as we “paint” them sometime, no?

Then back then someone pointed that Front Wheel Drive cars are actually doing better in this specific type of test, but do worse on the skidpad. So, here some more number from well known FWD cars only:

Acura 3.2 CL Type S ……………….. 60.1
Acura 3.2 TL Type S ………………… 64.0
Dodge SRT-4 …………………………. 64.8
Ford SVT Focus ……………………… 65.2
Honda Civic Si ……………………….. 64.6
Mitsubishi Eclipse GT ………………. 61.3
Nissan Sentra SE-R Spec V ……….. 64.6
Volvo S 60 T5 ................................. 61.8
Volvo V40 ...................................... 62.4


The funny thing? There is this 1,130,000$ Ameritech McLaren F1 has slalom speed of ... 64.5 mph, same as out NB Turbo S.

Ok, enough for now. You all have a good read through the weekend, later on I will post the other (and last) favorite thread I have, which brings even more food for thoughts. Enjoy the weekend!
 

jackbombay

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Joined
Mar 12, 2002
Location
Diesel knows best
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A4 Jetta
But they didn't come to Portland for the maximum possible crossing speed of 12th and Belmont (west on belmont) without the front of the car scraping. With stock suspension my jetta would scrape the nose at anything over 27 MPH (the speed limit is 35) and with my bilstiens and VR6 springs up front I crossed it at 45 and didnt scrape, I didn't try it any faster than that. That's a minimum of %66 better than stock.:)

It's clear that when grip is concerned the stock suspension does quite well, but it just does not feel as fun, the dramamine bills alone incured from the stock suspension were killing me, plus I was tired of constantly worrying about bottoming out the front of the car.
 

IndigoBlueWagon

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Location
South of Boston
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'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
This is interesting stuff to consider. I'm still musing over the differences between my A3 and A4, and I have a couple more observations. Both cars have Koni Reds and Sumitomo (well, Falken, same company I believe) tires. Both 195 series (50 on the A3, 65 on the A4). Stock springs and Shine bar on the A4, Neuspeed Sofsports and Neuspeed 28mm rear bar on the A3. And the A3 feels more nimble, more predictable, and more controllable as you reach its cornering limit than the A4. The A4 really feels like it's just washing out at the limit, overwhelming the front tires. I think it's a combination of unfavorable geometry and additional weight (by my calculations the A4 wagon is about 450 lbs heavier than the A3 sedan). At 3-5/10s the A4 feels crisp, responsive, and like it's on rails. But push harder and it starts to feel like a Camry. When I had 16" wheels and 205 series tires it didn't feel as much like this. The A3, on the other hand, feels great all the way to the limit, even though at the limit it's still understeering (gently). On the track last weekend I could do all kinds of stupid things like lifting the accellerator during a corner, changing turning radius, etc. and it didn't mind. I probably was short of its absolute limit, but still it was very predictable.

Two other thoughts: Saloms favor front-heavy understeering cars, I beleive, because they're more predictable. Skidpads and the track favor a balance between steering and driving wheels because they need to leverage all four tires to get the best speed. This is also why Miatas are so much fun on the track and do well in tight turns--even weight distribution and rear drive.

In 1974 Road & Track did a comparasion of sports cars, and it included the Opel GT, MGB, Fiat 124, and Porsche 914. The car that posted the best track times: The MG! This was a car that was in its 20th year of production with a suspension that was much older still (remember lever shocks?). But the balanced weight distribution, good suspension design (live rear axle, too), and responsive steering made it a quick car. The Opel had terminal understeer, and the Porsche was hard to drive at the limit and underpowered.
 

mr.mindless

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Joined
Jan 23, 2006
Location
Rochester, NY
TDI
2002 Galactic Blue Jetta GLS
Just wanted to chime in with a bit of fresh expirience, at least for me.

I finally had the nice, dry day that I'd been waiting for and got my Neuspeed 28mm RSB installed. I set it to full soft, though I have no numbers so that's pretty semantic for now. Maybe someone can find the numbers for what sort of difference the Nuespeed, H&R and Shine bars make at all their possible settings, or at least make reasonable approximations.

Anyway, I have not yet found the limit on dry pavement (with all season 195s) but the rear breakaway on gravel and especially on peppered pavement is certainly more sudden and severe, and not something that I think "average" drivers could deal with in a panic situation (my view of the "average" driver is rather dismal, and I think most people upgrading their cars are probably above average just because they're capable of paying attention to their handling in any way shape or form).

I would love the chance for a track day to compare real speeds & times with no bar, full soft, middle and full stiff. I may have an opportunity to do that sometime soon. A more consistant driver would be far more valuable though, I'd expect my lap times to very wildly even if all else was the same.

I think something important to consider (in addition to the very real possible safety ramifications) is why one changes their suspension setup. For a street driven car, feeling good at 7/10 is more important than being fastest at 10/10 most of the time. That's my attitude - feeling good is more important than really being fast since this *is* a street driven car, and in fact my commuter car. Just a bit of an aside I was thinking about recently.
 
Joined
Apr 11, 2006
Location
Berkeley, CA
Speed? or Fun?

The little Honda Fit Sport (Jazz) just did 71+ mph in the Car and Driver slalom...

Pyce makes a very good point. The raw speed gains from modifications to street cars are very small... indeed a joke, for a street car. Many mods gain a little of something over here, and lose a bunch of something over there. Most are not very sensible for a street car, especially in absolute speed terms.

But... thats ok! Street cars are about feel and feedback, not raw speed. (Perhaps we could go back to the different categories of modder's presented by Ceilidh, and deal with one at a time. Priorities range all over the place.) But I think most of the dissatisfaction over Mk4 handling at least, which leads to many of the mods being done, is about the feel. My Mk4 is very competent and fast and safe -- I bought it as a "GT" car, and its good at that. But it doesn't feel very 'sporty' or 'nimble'. It feels fairly heavy and ponderous. This is what most people want to improve. Can it be done without compromising the other good 'GT' qualities? Probably not. And that is important, yes.

As a longtime VW man I've owned 5 Mk1's (including a rally car and an ice racer), 2 Mk2's (including a rally car), a Mk3 and now a MK4. Now there's the Mk5. The Mk4 is clearly a competent and safe handler, but all the others are just more fun to drive, IMHO. Why is that?

I understand very well all the tech background covered so far in this thread, but I realize I don't have a full understanding of what makes a FUN nimble car, technically. And I think if we are talking about street cars, this is where the smart mods (if any) for Mk4's need to be found. My vote is for the discussion to get into this.


[ .....moved my ongoing side-track "my rear anti-roll bar = good" comments to the RARB thread created by Ceilidh for the purpose...... to help keep this thread as clean as possible....Carry on chaps. ]

Live and let drive.

Cheers.
 
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mr.mindless

Veteran Member
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Jan 23, 2006
Location
Rochester, NY
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2002 Galactic Blue Jetta GLS
wishboneracing said:
Street cars are about feel and feedback, not raw speed.
.....
I think most of the dissatisfaction over Mk4 handling at least, which leads to many of the mods being done, is about the feel.
...
I don't have a full understanding of what makes a FUN nimble car, technically. And I think if we are talking about street cars, this is where the smart mods (if any) for Mk4's need to be found. My vote is for the discussion to get into this.
I agree completely, and it does seem to be steering itself there and covering a LOT of extremely interesting ground on the way.

Also, it would be great if you could dig up that data on the different rear bars. I wouldn't think a bar stiffer than my H&R 28mm could be considered a 'street' bar. It's plenty wonky, trust me.
I was thinking about this a bit. I think we may be able to "fake" this information well enough for a mildly meaningful discussion. Assuming all three availible bars mount similarly (stiffening the twist beam rearend by going from the wheel hubs to two mounts on the beam), with measurements of the bar diameter, spread between the mounts on the beam, and "leverage" on the bar, as in distance from the bar centerline at the bushings to wherever the suspension acts on the ends of the bar as well as the distance from the bushings to the links to account for bending, we may have something to compare. This would count on them all being made of the same material with the same hardening process to be meaningful though, which is dubious. I would be surprised if the 28mm Nuespeed is exactly as flexible in torsion or in bending as the 28mm H&R....

Thoughts? Is there a better way to do this than figuring on paper, considering many of us will have different springs so car-to-car may not be as meaningful?
 
Joined
Apr 11, 2006
Location
Berkeley, CA
IndigoBlueWagon said:
. I'm still musing over the differences between my A3 and A4..... tires. Both 195 series (50 on the A3, 65 on the A4).
Hi IBWagon, are those tire sizes correct? ... 50 series on the Mk3, 65 on the Mk4? If so that is most of the difference right there. The lower profile tires will have a much different feel, esp. near the limit. And the same 195 width with those extra 450 lbs to carry, that sure doesn't help. Can't really compare. Or have you tried swapping tires?

Also, I believe the Mk3 did have a more favourable front LCA angle (higher inner).
 

Golf_GTDI

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Joined
Jun 12, 2004
Location
Logan Ohio, USA
TDI
2001 Golf GLS
I'm sure both have been busy as are many of us. With that said I think they may also want to try to keep this as focused as possible. For myself I would like to see as many aspects of the art touched upon and developed as possible but I'll let them dictate those terms.
 

jjvincent

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Joined
Jun 3, 2002
Location
Bethlehem, PA
TDI
Jetta, 2K, Green
It's nice to see that someone posts some good suspension information. I have to deal with this stuff all of the time. The only difference is that I have to do it with a BMW. I suggest that anyone wanting to see how some people get FWD cars to handle, go to a Grand-Am Cup event. These cars are close to stock but you get to see what people do to overcome different problems that exist with stock cars. Even our BMW's have been modified heavily to run at our mandated 3.5" minimum ride height rule. If you are ever at a Grand-Am event, stop by and I'll show what was done to make the car handle. We run in GT and are allowed to move the suspension pickup points up to 1". It's amazing what that 1" will do for a car.
 

sportsguy

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Mar 11, 2005
Location
Seattle-ish
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2014 Beetle DSG TDI
First off, a BIG thanks guys - this is real info and educational info. MUCH better than most of what tends to float through boards these days.

The TDICLUB has one of the best cultures I've ever encountered - anywhere (Bad attitudes at a popular Jeep-focused posting forum "forced" me to start my own websites to collect data for users, rather than them having to experience the poor attitudes shown when asking questions... :( )

Here's my only question:

Have we gotten to the "GT" portion yet? Did I miss the discussion on that? I've read everything to date (some parts a few times) , and generally understand it all. Maybe I just missed a title for a section?

I am particularly interested in following that portion of things, as I'm considering a drive to the US to get the Shine system installed in my MK4 this fall - but after recently adding 225/45/17 Michelin Sports (all-season ones), and being completely impressed with the "new" handling of the car, in addition to the retained ride quality (stock suspension), I'm asking myself if the direction should be "more" brakes up front, and perhaps some more power through chip-tuning... ;)

I don't autocross, the car is a commuter, though I sometimes harass Mini Coopers on twisty local roads... ;)

Truly these threads have confirmed some lingering thoughts I'd had on the inherent "goodness" built into our chassis from the factory. They've also opened my eyes, numerically, to how small many of the gains can actually be in the real world. I'm a numbers guy who likes "feel", so for me, I'll give feel if I know the numbers back the reality. If the stock suspension does almost as good a job as aftermarket (by the numbers), I'll take the edge in safety (built in) and give some "feel".

Anyway, thanks again so very much for all your time, effort and willingness to share your knowledge.

If you guys ever need a hand proof-reading, drop me a note - happy to lend some time to this worthwhile discussion.

Duane
 

Fyrman

Top Post Dawg
Joined
Sep 27, 2004
Location
Hammonds Plains, NS, Canada
TDI
Jetta, 2001, Black
Wow... big thanx to you guys for putting together shuch an awesome suspension resource.

Ceilidh, Peter Pyce... you guys rock, keep the info flowing.

I think it's time that this thread got nominated for a sticky! :cool:
 

peter pyce

Veteran Member
Joined
Nov 6, 2001
Sorry everybody! I am extremely busy with other things in life and it may not get any better, but here is quickly on the GT setup and few other things. Note: this is a copy-paste, all written by Ceilidh and ideally I would have read it again (as it was written more than two years ago!) and perhaps see if we have "discovered" some new things that would make the writtne more accurate, but I really can not afford to sit down and read it right now, so take it as a baseline on which later perhaps we can edit and add/remove things..... so, here it is, unchanged, all his the the end:

8) GT Suspensions

Ok, at last we turn to GT suspensions. =)

GT Reminder

First, a quick review (for more detail, look back in the "Who We Are" post):

A GT suspension is one that allows for fast, effortless, reasonably-comfortable travel on varying and difficult roads. Unlike the Agility-is-Everything Autocross suspension, and also unlike the We're-Always-at-the-Limits road race suspension, the GT setup has to have:

1) excellent roadholding (good mechanical grip) on a variety of road surfaces

2) forgiveness for unexpected events

3) handling that is consistent under changing road, weather, and load conditions

4) responsiveness to good throttle/brake/steering technique

5) reasonable ride comfort

Picking an appropriate tradeoff between these 5 characteristics is tricky, and you cannot optimize for all of them at once. A race suspension will lose out on #2 and #5 (and often #3); autocross suspensions often lack #1,2,3,5; and a poorly designed aftermarket kit (particularly one directed toward the Darters) is capable of losing all 5 simultaneously.

Stock Reminder

As discussed earlier, the stock suspension is not that bad at all, as it possesses abundant amounts of #2,3,4,5. It does so by artificially (via adverse camber on the front tires) introducing noticeable understeer at even low speeds; by increasing the amount of understeer with cornering speed in an extremely progressive and predictable fashion; and by hitting extremely unpleasant amounts of understeer long before the front tires actually run out of grip. As a result, the stock car feels "natural": drive too fast, and the front washes out; correct for the understeer by turning the wheel harder, and the car responds to the steering; take your foot off the gas to slow down, and whilst the front end will tuck in, a normal driver can readily avert a spin; apply classical corner-entry and exit techniques, and the car will corner much faster than normal street traffic.

Where the stock suspension loses out big time is in Extreme Agility (which is not even on the list of GT priorities, but which is perhaps #1 for an autocrosser), and -- more importantly here -- in #1: Roadholding. Because the stock understeer sets in so early and becomes so pronounced at moderate speeds, the usable level of grip is far below what some drivers would like (I say "usable" because the absolute level of grip (as indicated by skidpad g-forces) is only about 10-15% lower than those of purer performance cars; it's just that the understeer becomes (by design) so unpleasant at even moderate speeds that most people get nowhere the absolute limits).

The challenge with a GT setup is therefore to improve #1 (Roadholding) without losing out everywhere else. In general, it's not hard to increase #4 (Handling Responsiveness) at the same time as #1, so the tradeoff is in improving #1,4 without losing too much of #2,3,5.

STAGE 1: Install Koni Shocks on all 4 Corners

[note from peter as of today(year 2006): Install Koni on all four corners was back in the days (2-3 years ago when this was written) when we knew very little about dampers, we did not know how to work on them, what could be done with them, etc. So, back then, a set of Konis was something more comfortable than a set of Bilsteins, and on top of that the Konis were adjustable, so we ended up with those, but as of today, the GT setup could be a very wide variation of dampers, which offer very different flavors and there is one (set) for every taste and perhaps that is where a more detailed discussion will happen later - precisely on what the different dampers bring to the GT picture]

The above paragraph (about the tradeoffs between goals #1-5) is a general statement that applies to almost all passenger cars. With the Golf/Jetta IV, there is an additional challenge: the rear suspension design (the classic twist-beam) has, among several other failings, an inherently poor ability to absorb sharp impacts (meaning that when you hit a sharp-edged pothole, expansion strip, or ridge, the suspension transmits a "BANG!" into the cabin). This failing (which is one reason why the Golf/Jetta V is going to a multilink rear, and why none of the FWD cars that are known to outhandle the Golf IV -- e.g., Focus, Mini -- use a twist beam) makes it very hard to stiffen the rear without quickly losing ride comfort.

On the damping side, the need to keep the rear end soft means that the stock rear shocks are fairly soft on high-piston-velocity damping (high piston-velocity controls bumps; low piston-velocity controls pitch, roll, and heave). Soft high-piston velocity requires similarly soft Low-piston-velocity, so the stock rear shocks are too soft for good handling. In turn, the soft rear means that unfortunately the front must be underdamped as well: as Peter Pyce & I (Ceilidh) have independently noted, when front & rear damping rates are grossly unequal, a very annoying jiggling pitch sets in, making the ride uncomfortable. Hence although the front suspension can inherently take firmer damping than can the rear, the damping there too must be softened, so as to match the rear.

The upshot is that the stock Golf/Jetta IV is severely underdamped at low-piston-velocity, and hence it rolls, pitches, heaves, and generally responds to handling inputs with much less control than one would like.
Thus an excellent first GT step is to improve the damping. Within limits, it is possible to increase the low-piston-velocity damping (which would improve handling) in a shock without unduly increasing the high-piston-velocity damping (which would degrade ride comfort): such a shock is said to be highly "digressive" (opposite of progressive). (With such a shock, the damping forces ramp up very quickly at low piston speeds, but then rise more slowly if the piston begins moving faster.) It is difficult to make a shock that is highly but smoothly digressive, however, and it is even harder to have such a shock retain its nice characteristics over tens of thousands of miles. Therefore well-designed digressive shocks like the Koni Sports and Bilstein HDs are fairly costly.

With the Golf/Jetta IV, unfortunately, it appears to be impossible to get an even highly-digressive shock to be simultaneously soft enough at high-piston-speeds for bumps, while remaining stiff enough at low-piston-speeds for good handling. Hence the Koni Sport (which Peter Pyce's experiments seem to highly recommend over the Bilsteins) has to cheat:

a) to get enough low-speed damping for body control, the Koni Yellows are fairly stiff on bumps. Careful adjustment can do a lot to improve comfort (as both Pyce & Ceilidh have found), but the end result is still "busier" and firmer than stock.

b) given the overall stiff damping required, Koni appears to have specced a twin-tube design (they manufacture monotubes as well, for other applications) so that the shock is not particularly "quick-acting": when the shock begins to move (as when you hit a bump), it does very little damping for a few millimeters, and the damping force "rolls" in rather than comes in with a bang. This characteristic is undesirable for a very stiffly sprung racing car (which is why racing cars use monotube Konis, Bilsteins, Penskes, etc.), but in this application it softens the initial impact from potholes and the like. Hence by using the slower-acting twin tube design, Koni can retain reasonable comfort while increasing overall stiffness for better handling.

The upshot of the above is that, based on Peter's experiments, the extremely quick-acting Bilstein HD (which is an excellent shock, one that Ceilidh has had good experience with elsewhere) is NOT a good fitment for a GT-tuned Golf or Jetta IV. If a driver knows he will be driving on roads that do not have sharp high-speed impacts (no sharp-edged potholes or expansion strips on the highways), then Bilstein HDs should work fine. But if ride comfort is an issue, and if local roads (particularly high-speed roads) have sharp-edged bumps, it appears that Konis are the way to go.

In any event, the stock suspension is not bad at all for a GT suspension, save that it severely de-emphasizes #1 (Roadholding), and in stock form the shocks are so underdamped that body motions obscure the handling qualities. Replacing the stock shocks with Koni Sports all around will slightly degrade #5 (Ride Comfort) while improving #1-4 (everything else), chiefly by controlling the body motions and allowing the suspension to work as originally intended. As such it is an excellent first cut at the GT setup.

Next installment: we'll take a look at the Rear-Antiroll-Bar-on-a-Stock-Suspension setup, and try to sort through why some extremely knowledgeable and fair-minded people (e.g., John A) advocate it, while other extremely knowledgeable experts (e.g., Dick Shine, who even sells an excellent rear bar) caution against it.

Cheers, everyone! =)

- Ceilidh
 
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