www.tdiclub.com

Economy - Longevity - Performance
The #1 Source of TDI Information on the Web!
Forums Articles Links Meets
Orders TDI Club Cards TDIFest 2016 Gone, but not forgotten VAG-Com List Unit Conversions TDIClub Chat Thank You




Go Back   TDIClub Forums > VW TDI Discussion Areas > Upgrades (non TDI Engine related)

Upgrades (non TDI Engine related) The place of handling, lighting and other upgrades that do not relate to the performance or economy of the TDI engine. In other words upgrades to your TDI that don't fit into TDI Fuel Economy & TDI Engine Enhancements.Please note the Performance Disclaimer

Reply
 
Thread Tools
Old March 20th, 2006, 23:12   #1
Ceilidh
Newbie
 
Join Date: Mar 2006
Default What is Handling?

Hello Everyone,

As some of you may know, I'm just a guest here, as I own a GTI, not a TDI, and have only recently registered with your very fine forum. But I'm a friend of Peter (Pyce), and having received an email from Peter saying that he's going to consolidate some of our postings from the Vortex into something a bit more accessible to the folks here (the Vortex postings are scattered amongst a host of rambling threads), I thought I'd get things started with a little introduction to things pertaining to vehicle dynamics and suspensions.

Now, I don't know exactly what Peter has in mind, so the format of things might change as we go along, but perhaps a good way to start would be to clarify some oft-confusing terms so that everyone's on the same page. Hence I've called this thread "What is Handling?", and we'll use it to nail down what different handling goals can be, and what basic steps one can use to accomplish those goals. Content-wise, we'll wait for Peter's lead (and it'll probably take a few weeks to fully get things going), but for this first post, we'll take a quick and cursory look at an oft-discussed handling subcategory:

What is Understeer?

So let's get started!

* * * * * *

WHAT IS UNDERSTEER?

Back when Peter and I were posting on the Vortex, sooner or later we'd log on one day to a thread we'd been laboring on, and find something like the following:

Post 1: The understeer on my car is awful. How do I get rid of it?
Post 2: Do "X".
Post 3: Do "Y".
Post 4: I did X, and it didn't help at all.
Post 5: Well, I did X, and my understeer disappeared.
Post 6: You're all crazy. Our cars understeer, and you can't do anything about it.
Post 3a: Do "Y".
Post 7: I did Z, and it really helped reduce my understeer. But the car wants to spin now -- my friend's Subaru/Honda/BMW/etc. understeers even less than my car does, and it doesn't want to spin; what should I do to make my car like that too?
Post 8: I'm a racer, and I've done X, Z, A, B, C, D (etc., etc., etc.) to my car, and it handles like a dream!! It wouldn't be safe for any of you to do that to your cars, because you're not good enough drivers. But because I'm so skilled, I can take it. Let me tell you about an exciting incident I had last week, where my car would have crashed if it hadn't been for my lightning fast reflexes......
Post 3b: Why doesn't anyone do "Y"? I'm telling you, "Y" really works!!
Post 9: Hey Racer, that's so cool! My car has X, A, B, E, F, and a homebuilt G that I made out of two hoseclamps, an ironing board, and something my dog brought home last year. If I did D as well, do you think maybe that....
etc.
etc.
etc.



Anyway, besides convincing people like Peter and yours truly that our time is perhaps better spent doing virtually anything besides posting anymore on the Vortex, exchanges like the above usually resulted from disagreements on what "understeer" really means -- which is why we should clear it up from the start. To wit:

The problem with "Understeer" is that it has a very specific, narrow meaning in the vehicle dynamics handbooks, and a very broad definition in the popular press (especially on web forums and in most all aftermarket advertisements). Thus people complaining about understeer are often (through no fault of their own) really complaining about something that's only indirectly related to true understeer, whilst others offer solutions to "understeer" that are solutions to entirely different problems.

So what is "Understeer"?

Judging from web posts and advertisements, it looks like "understeer" for many people is a vehicle flaw that prevents the car from turning incisively into a corner; that numbs the steering and causes a rubbery feel just when one would most like to keenly sense the road-tire interaction; that causes the car to drift sideways in a corner, tires squealing and howling ineffectually; that reduces the car's agility and ability to dart & weave back and forth; and that causes a car to plunge straight ahead when a turn is taken too fast.

But from a vehicle dynamics perspective, however, understeer is directly related to only one of the above "flaws", and has only an indirect (and often weak) link to all of the others. Thus if you're trying to correct the above problems, and blithely follow tried & true solutions that are known to reduce understeer, you might notice very little "improvement" in all but one of the vehicle "flaws", and you might introduce a new set of problems you never expected.

To explain: from a vehicle dynamics perspective, "understeer" is a stability term -- if a car is subjected to a sideforce (caused by a gust of wind, a sloped roadbed, a pothole, cornering g's, magnetic attraction, an attack by crazed gerbils, whatever), it can do one of three things:

1) Despite being shoved sideways, it can proceed merrily on its way, in the same direction it was originally travelling;

2) It can turn away from the crazed gerbils, etc.;

3) Or it can turn towards the gerbils, windgust, etc.

#1 is the condition of Neutral steer; #2 is Understeer; and #3 is Oversteer.

The three steer conditions have stability implications because the moment a car begins to turn, it experiences an additional sideload due to cornering g's. In the Neutral case, the car doesn't turn, so there's no additional sideload. In the Understeer case, the cornering sideload "fights" the original sideload, and thus the amount of turning decays with time (e.g., if a gust of wind shoves the car to the left, an Understeering car begins to turn to the left; but then the (right-directed) centrifugal force from this leftward turn counteracts the original shove, and eventually the car straightens out). In the Oversteering case, the cornering sideload augments the original sideload, and the turn becomes tighter and tighter (e.g., when the wind shoves the car to the left, the car turns towards the right, which causes centrifugal force to shove still harder towards the left, which causes the rightward turn to tighten still further, etc....), until the car finally spins.

Think about the implicatons of the above for a moment!: if a car is set up to be truly Oversteering, then any sideforce -- any gust of wind, pothole, slope, crazed gerbil, etc. -- will cause the car to spiral into a spin, unless of course the driver intervenes in a timely fashion by turning the steering wheel in the right direction. Conversely, an Understeering car is inherently stable: when you shove it to one side, it turns away from the shove and then tries to straighten out, without ever wanting to spin. This Understeering situation is inherently much, much safer, and thus it should come as no surprise that essentially all passenger cars are designed to understeer: if they were not, then high-speed driving would be a continuous white-knuckle struggle to avoid spinning off the road -- even if the road is dead-arrow straight.

So to reiterate: All Passenger Cars Are Designed to Understeer, and that is A Very Very Good Thing.

Given, then, that Understeer is a Good Thing, why do people hate it? Here's where we get to the crux of the confusion: there are legitimate reasons to dislike understeer, and there are confusing reasons. Let's look at the legitimate reasons first:

Legitimate Reason #1:
Even many (and perhaps most) racecars are set up to understeer mildly -- but HEAVY understeer will cause problems when a car is driven at the limit. Understeer causes a car to turn away from the center of a corner, and thus a heavily-understeering race car will try to plow straight into the concrete walls/ tire walls/ gravel traps lining the outside corner of a racetrack, giving the driver a brilliant view of what he's about to hit. Racing drivers really dislike having such a view, and they would much prefer the car to be less stable, so that they can try to "pitch" it into the corner and adjust their trajectory. For this reason, a common racing quote is "Oversteer is where the passenger is scared; Understeer is where the driver is scared.", and a lot of race car tuning is spent to eliminate heavy understeer, especially on low-speed, tight corners, where such understeer tends to be most severe.

Legitimate Reason #2:
Similarly, excessively heavy understeer on the street can have us plowing off the road during rainstorms or snowstorms, with the wheel cranked hard over while the car charges straight ahead, and that's unpleasant too.

Legitimate Reason #3:
And then there are people like Peter, who like to be able to bring the rear end of the car around on occasion, just for fun.

There are other good reasons for disliking excessive understeer, and we can extend the above list quite a bit -- but notice something: nowhere in any of the discussion thus far have we said anything about steering response, or corner entry turn-in, or left-right darting agility, or road feel. Understeer IS indirectly related to these other characteristics, in that a heavily understeering car is a very stable car, and stability works against lightning reflexes, but the relation isn't direct. Indeed, it's possible to have an understeering car that has great reflexes, or conversely a fairly neutral car with comparatively sluggish reflexes (at various times in his experiments, Peter's car has probably sat in this latter category: a TDI with minimal understeer but relatively slow steering response). Agility and Understeer are in many respects two entirely different things.

Why does the above matter? Well, it matters because the chassis and suspension modifications you make to reduce understeer are not the same changes you make to directly improve agility and steering response, and in a fairly common extreme case, it's possible to so reduce understeer in a misguided (and failed) attempt at improving agility, that the car becomes dangerous to drive on the street (especially in poor weather conditions). This last predicament is one that several Vortexers have encountered, particularly when they installed ever-increasingly stiff rear antiroll bars on otherwise stock cars, in a futile attempt at increasing turn-in steering response via "reduced understeer".

As for what chassis mods work towards reducing understeer versus what mods work towards agility -- well, that'll be in future installments, depending upon what direction Peter wants to take things. Cheers til then!

- Ceilidh

Last edited by Ceilidh; March 20th, 2006 at 23:22.
Ceilidh is offline   Reply With Quote
Old March 20th, 2006, 23:41   #2
nicklockard
Torque Dorque
 
nicklockard's Avatar
 
Join Date: Aug 2004
Location: Arizona
Fuel Economy: No data yet.
Default Thank you. Thank you. Thank you!

Thank you for starting this discussion!

Quote:
Originally Posted by ceilidh
Conversely, an Understeering car is inherently stable: when you shove it to one side, it turns away from the shove and then tries to straighten out, without ever wanting to spin. This Understeering situation is inherently much, much safer, and thus it should come as no surprise that essentially all passenger cars are designed to understeer: if they were not, then high-speed driving would be a continuous white-knuckle struggle to avoid spinning off the road -- even if the road is dead-arrow straight.


(snipped)

Why does the above matter? Well, it matters because the chassis and suspension modifications you make to reduce understeer are not the same changes you make to directly improve agility and steering response, and in a fairly common extreme case, it's possible to so reduce understeer in a misguided (and failed) attempt at improving agility, that the car becomes dangerous to drive on the street (especially in poor weather conditions). This last predicament is one that several Vortexers have encountered, particularly when they installed ever-increasingly stiff rear antiroll bars on otherwise stock cars, in a futile attempt at increasing turn-in steering response via "reduced understeer".

(emphasis added)
I look forward to seeing this discussion develop and evolve. Thanks!
nicklockard is offline   Reply With Quote
Old March 20th, 2006, 23:59   #3
BoosTDIt
Veteran Member
 
BoosTDIt's Avatar
 
Join Date: Jan 2003
Location: DC area - Fairfax,VA
Fuel Economy: hmm 1 tank best 768m. & light went on - 43 average
Default

Yep... I too can't wait to learn and absorb even more information on the subjet than i already have through scattered posts here and Vortex!

And i can assure you the audience here is somewhat more mature (intelectualy not age) thus the topic will remain in its intended educational form.

And it'll be preserved in a better way here at TDIClub, rather than the gazzilion multi-branch thread giant Vortex...
__________________
'I didn't mod my car to be faster/better than other cars, I modded my car so its faster/better than it was before the mod'

mods - JunkInDaTrunk
BoosTDIt is offline   Reply With Quote
Old March 21st, 2006, 01:32   #4
TdiAvenger
Veteran Member
 
TdiAvenger's Avatar
 
Join Date: Jul 2004
Location: Arlington Texas
Default

page 1
TdiAvenger is offline   Reply With Quote
Old March 21st, 2006, 05:18   #5
somepunk22
Veteran Member
 
Join Date: May 2004
Location: Minnesota
Default

Increasing agility.... Are you guys going to invert the dampers? Or maybe just the rears? In a earlier fsd post of Peter's, he quickly mentions this.
somepunk22 is offline   Reply With Quote
Old March 21st, 2006, 10:40   #6
peter pyce
Veteran Member
 
Join Date: Nov 2001
Default

Hi Winston!

Quote:
Originally Posted by Ceilidh
.....I'm just a guest here.....


We are all guests here, except the guy(s) who pays to keep this site going J

I am glad you decided to come and dedicate time and effort to put few things together, so they do not get lost in space. It had been incredible, what, three years now (?) since we got in touch, and so much had been written and said, it will be shame if it gets lost.

I particularly think your amazing write up on the “Stock” setup from that long thread is something worth reading for everyone who wants to learn little bit more about what a Stock VW is all about. I have been searching through the Internet for few years now, in attempt to learn as much as possible on suspension, and I have never seen any text of this magnitude that talks about a stock setup. Everyone is so, so busy with “reporting” handling characteristics on modified cars, but almost no one spends time to understand what the stock car is to begin with, especially on a case like the VW, which definitely is not a sport car and unless some big modifications are done – it will never be. Also, I particularly like the text that “nicklockard” quote above – it is the essential of where the trouble starts when modifying a car! The goal is not so clear and the results are just perceived feelings, meanwhile the new setup is a lot worse in so many other aspects, but that is either overlooked or simply not even detected due to pure lack of experience and knowledge.

So, let me go find the long posts on the Stock setup and perhaps we can simply copy-paste them and go over one more time and then perhaps use those as a base for some sound conversation. It had been more than two years ago, so I am sure we can add something to that master piece.
peter pyce is offline   Reply With Quote
Old March 21st, 2006, 12:09   #7
peter pyce
Veteran Member
 
Join Date: Nov 2001
Default

Let's continue with this post of Ceilidh's..... it is, funny enough, from exactly two years ago This is about scene-setting here with a little discussion of endgoals and driver types:

The following is a copy-paste, but will not use quotes, so it will be easier to refer/quote later. His post all the way to the end:

If you look closely at the posts to the suspension forum, you'll see that suspension enthusiasts tend to fall into several more-or-less clearly defined groups. We'll ignore those who want lowering for looks, as well as the people who simultaneously want pinpoint handling precision, a luxury ride, fantastic grip, and failsafe emergency behaviour (advice to these souls: save up for a nicer car). The remainder fall roughly into 5 categories (I'm grossly oversimplifying here!): there are track enthusiasts, divided between autocross and road-course aficionados, and then there are the roadies, whose 3 categories I'll explain in a moment. (As discussed in the earlier installment (#2), the track setups are considerably closer to "neutral" than are the road suspensions, and only the very skilled or commendably cautious should be running serious track/autocross cars on public roads.) We'll go through these categories one by one:

1) Track-Based Suspensions: Autocross

Autocrossers live in a flat, low-speed world with endless sharp corners. These characteristics -- the relative smoothness of the autocross tracks (e.g., parking lots with cones), the need for lightning-fast corner entry and left-right transitions between corners, and the low speeds necessitated by the constant tight turning -- define the autocross suspension. As we'll see in a later installment, there's probably more room for variety in a Golf/Jetta autocross suspension than anywhere else, and it's here that one might get away with the ultra stiff springs, big antiroll bars, and meaty wide tires that are the staple of common speed shops. That's not to say that the aforementioned parts are the fastest or best way to go, but at least in autocross they have a chance.

2) Track-Based: Road Course

Compared to an autocross course, a true road-racing track allows for much higher speeds and a much more flowing mode of travel. Agility in transitions starts to matter less than stability under trail-braking and an ability to put down power on corner exit. Although the surface of a good track is about as smooth as anything a car will drive on, the speeds are high enough to begin putting a premium on absorbing bumps while maintaining traction. The requirements of a good road-racing suspension start to converge on those of a good street suspension, and a dialed-back road-race setup (i.e., a road-race setup that's been given better ride comfort and more stabilizing understeer) can form the basis of a fast road car.

3) Street-Based: The Darter

"Darter" is not an official term, but it is descriptive. A darter is a person who wants his car to have the instantaneous, solid, no-roll response of a go-kart. "Handling" here equates to an ability to zig-zag through turns so suddenly that passengers lunge frantically for the grab handles and loose french fries go flying through the cabin, or to change lanes in a quick left-right snick-snick that supposedly looks cool but in fact is only dangerous -- it's sort of the Super Mario/ Nintendo view of the automotive world. I was a darter once, and a lot of sub-24 male car enthusiasts seem to start off in this category. Unfortunately, darters are rarely happy people (not least because, if darting is the goal, the Golf/Jetta IV is the wrong car). For the VW-loving darter, the car always rolls too much, the steering is always too slow, there's always too much understeer, and friends' Hondas and Integras are always better. Darters play an important role in the VW tuning ecosystem by single-handedly keeping the smaller tuning shops alive: it is the darters each year who go through enormous quantities of springs, shocks, bars, coilovers, urethane bushings, camber plates, rims, tires, spacers, spindles, strut tower braces, steering racks, spherical bearings, and general miscellaneous stuff, all guaranteed by the vendors to "tighten the handling while eliminating understeer!". There's nothing wrong with being a darter (as I said, I used to be one myself), but it's a frustrating existence if your car is a Golf/Jetta IV, and ultimately darters either gravitate towards autocross setups that don't work for the real world ("Selling complete suspension!! Wife having baby -- must sell!!"), or else they give up by selling their VW, or by becoming a Grand Tourer.... In any event, there is no suspension setup that is the ultimate Golf/Jetta IV street Darter -- if darting is the goal, you will need a different car.

4) Street-Based: The GT's

The acronym "GT" originally referred to Gran Turismo (Grand Touring) cars that were fast, comfortable, and effortless at rapidly covering ground on difficult, twisting roads (supposedly they developed when Europe still didn't have much in the way of superhighways).. And the GT version of the Golf/Jetta is what most non-darter street enthusiasts are looking for. If you fall in this group, you're looking for something that has a lot of grip, is reasonably comfortable, possesses good stability, and is relatively forgiving (so that you can converse with your significant other while zipping through the countryside). The setup for a good GT is essentially a dialed-back version of a good road-race car (with increased understeer and more comfort); the Shine SRSS is probably the exemplar here (although it apparently works well on the track as well), along with its softened permutations, and the GT enthusiast can essentially decide where on the ride vs. handling continuum he wants to be. We'll spend a good amount of time talking about the GT setup, when we eventually get to the appropriate installment.

5) Street-Based: Driving a Slow Car Fast

Finally, here is the smallest, least popular group, which I list primarily because I (Ceilidh) currently live here. A sad thing about aging is that some of us become steadily more boring and wimpy as the years go by, and eventually we resign ourselves to driving interminably behind the Volvo 240 with Delaware plates instead of searching for a way to pass it. When that happens, a "good" suspension becomes one that provides maximum feel, that responds somewhat to classical driving techniques even when driven at 3/10 to 5/10, and that possesses low enough limits (or more accurately, "perceived" limits) so that we get the occasional sensation we're actually driving. For people in this small category, a near stock setup with better damping (but skinny tires) is actually kind of nice.
So those are the categories. Each category has a different ultimate suspension solution (except for the Darters, who are doomed to disappointment), and a person wanting to modify his suspension had best figure out which category (or between which categories) is the one that really applies.

By the way, if you want to have some fun, go through this thread and try to guess which category the various vortexers currently live in. Yours truly (Ceilidh) started out as a Darter, went next to Road-Racing, before fear drove him to GT, and then boredom led him to Slow Car Fast. Peter (Pyce) apparently began as a GT, pushed that to an extreme, and is now slowly drifting in the direction of Slow Car Fast (though I think he's still in the GT realm).

Next installment: how the stock suspension works.
peter pyce is offline   Reply With Quote
Old March 21st, 2006, 16:10   #8
IndigoBlueWagon
TDIClub Enthusiast
Principal IDParts
Vendor
w/Business number
 
Join Date: Aug 2004
Location: South of Boston
Fuel Economy: 50/45/37
Default

Ah, slow car fast. I'd like to be the GT driver but reality puts me on crowded roads that makes me the third category.

And I learned about understeer and oversteer at an early age by learning to drive in various swing-axle Volkswagens and an Austin Healy Sprite. Talk about getting old. That was back in the days when not all cars understeered. Triumph Spitfire? Any Porsche?

I started out here as a darter, too. But now am on stock springs and Koni Reds on full soft. Life is good.
__________________
2002 Jetta wagon, 375K, RC3+; 1993 Mercedes-Benz 300D 2.5, 197K; 1997 Passat, 286K; '99.5 Golf, 259K; 2011 335d, 56K; 2015 Golf Sportwagen, 11K. Principal, http://www.idparts.com
Kid's cars: 2002 Golf TDI, 2002 Jetta TDI

Last edited by IndigoBlueWagon; March 21st, 2006 at 16:12.
IndigoBlueWagon is offline   Reply With Quote
Old March 21st, 2006, 16:46   #9
oldpoopie
 
oldpoopie's Avatar
 
Join Date: May 2001
Location: Portland Oregon
Default

Ahh. I'm #4. I've never had the opportunity to be a darter... I used to drive a '69 ford falcon, all stock. Then went to a '95 chevy tahoe.... Then to the golf with Shine. I've loved the shine setup from day one. The thing that amazes me is how much toe-in alignment can effect the twitchyness of the car. Point is, make sure your certain your toe alignment is set properly before judging any setup.
__________________
Pacific Northwest TRUSTED TDIClub mechanic

Email me, justgrow@gmail.com
oldpoopie is offline   Reply With Quote
Old March 21st, 2006, 17:58   #10
JetPuf
Veteran Member
 
JetPuf's Avatar
 
Join Date: Sep 2003
Location: Portland/Troutdale Oregon
Fuel Economy: loswest mpg 32 Towing, average 45, highest 53 hwy
Default

Quote:
Originally Posted by oldpoopie
The thing that amazes me is how much toe-in alignment can effect the twitchyness of the car.
When I first put in my TC's I had a bit of toe in, Yeah it was twitchy... on the way to the alignment shop.
__________________
White '98 NB TDI "Jetpuf" 310k miles Tune, Injectors, Turbo, Peloquin, 02J 6-Speed..
Gray 2010 X164 GL350 Bluetec 94k miles
Member of The Joneses
JetPuf is offline   Reply With Quote
Old March 23rd, 2006, 10:40   #11
Golf_GTDI
Veteran Member
 
Golf_GTDI's Avatar
 
Join Date: Jun 2004
Location: Logan Ohio, USA
Fuel Economy: 44mpg Avg.
Default

Great stuff. I look forward to see where this goes. I'm happy to see that we may be able to look at many aspects of handling and how they interact. I for one think I know where I would like to be on this above list of drivers but I'm not sure where I actually am.

I hope that my own efforts may in some way add a little something to the common good and find that I am paying a bit of a price in that I don't have a system that I'm all that happy with. Its also interesting that we bring up the stock system which as I recall was very stable but rather slow with minimal feel.

I could talk about what I feel now but I think that at this point I have learned enough to know that I know very little. I think I would have to try dozens of dampers and spring rates and many many tire combos before I could get close to a decent guess as to whats going on exactly.

I hope that as a group we can get a little closer to an understanding of what is going on with our cars and how we can get the effects that we want with minimal headache and less than endless testing.
__________________
www.rallyvw.com
Golf_GTDI is offline   Reply With Quote
Old March 25th, 2006, 01:44   #12
BoosTDIt
Veteran Member
 
BoosTDIt's Avatar
 
Join Date: Jan 2003
Location: DC area - Fairfax,VA
Fuel Economy: hmm 1 tank best 768m. & light went on - 43 average
Default

A bit out of topic (Mk4's) but...i think the Mk2's are GREAT Darters :-)
I know i had a few...lol

I'm in the Slow car Fast...aiming for GT ... but only the right type of GT... that's why i'll remain in Fast for a while :-)
__________________
'I didn't mod my car to be faster/better than other cars, I modded my car so its faster/better than it was before the mod'

mods - JunkInDaTrunk
BoosTDIt is offline   Reply With Quote
Old March 27th, 2006, 21:12   #13
Ceilidh
Newbie
 
Join Date: Mar 2006
Default Understeer, continued

Greetings again(!)

I think Peter's going to cut & paste a little more in a short while, so let me wrap up the understeer discusssion:

When we last left it, we had shown how "understeer" is a stability criterion, and we discussed how a car lacking basic understeer cannot be driven at high speeds, even in a straight line on a level road. Given that, we now ask: if all cars understeer, how is it that so many of them (e.g., mid-1960s Porsches) are said to oversteer?

The answer to the above question is one that most if not everyone on this forum already knows, but we'll discuss it for completeness: whatever the inherent balance of a car (whether it be neutral, understeering, or oversteering), the balance can be shifted -- to a considerable extent -- by what the driver does. Or in plainer English: a mildly understeering car can easily be made to oversteer by a skilled (or completely clueless!) driver, and the same car can be made to imitate a hopeless, understeering pig.

(Slight digression: there's a book somewhere out there (alas, I've no idea of the title or author, as I just leafed through it one day in a Philadelphia bookstore...) that showed Formula One cars going through a corner in a 1950s Grand Prix race. In that montage of photos, you could see Mike Hawthorn (British, wore a tie while racing!) muscling his front-engine Ferrari through the corner on successive laps: on one lap he was understeering, on another there was spectacular oversteer, on the next he was heavily understeering again, then still later he was in a neutral 4-wheel drift -- same car, same driver, same corner, same tires, same setup, almost the same fuel load from shot to shot. It's not that the car was changing; instead, Hawthorn (a gifted but inconsistent driver) was having trouble with his Ferrari's handling that day, and was trying different techniques in an attempt at finding a good, fast groove...)

The techniques that cause a car to under- or oversteer are the things you learn in a good driver's school or even in a good racedriving book, and we won't go into them here; instead, we'll just mention that many of the techniques hinge upon inducing fore & aft weight transfer via acceleration and braking, with the "heavier" end of the car generally winding up with more traction. What's important for this discussion is that this weight transfer has an almost unbelievably powerful effect on the car's handling balance -- regardless of whether or not the weight transfer is deliberate -- and it is very difficult to drive a car without causing these weight transfers to occur continually -- for good or ill.

It is because of the above situation -- that cars are extraordinarily sensitive to weight transfer, and weight transfer is extremely easy to invoke in the wrong way -- that street vehicles are not set up like race cars....

[Digressionary note #2: many car magazines will rave about some mondo sports car having "race car handling!!!!" -- but if you follow and read these magazines very carefully, you'll find that most auto journalists have never driven a true race car at speed on a race track; the ones that do (e.g., Peter Egan at Road & Track is a Formula Ford race driver) never, ever claim that a street vehicle (barring something like an Enzo) feels or handles like a race car -- the comparison is just absurd!]

...With race cars, the small amount of built-in understeer can be easily overcome by small amounts of forward weight transfer, and it's the driver's job to feed in that forward transfer only at appropriate times; if the driver screws up (e.g., as by reducing engine power midway through a corner), the car generally spins like a top. In contrast, a passenger car has to be set up so that it rarely or never spins, and in particular it must not spin when people do things that are "normal" from a human psychology point of view, but which are suicidal from a racecar point of view. The list of these things is fairly long, but a classic example is what people do when they enter a corner too fast, and the car begins to swing wide: the "normal", human thing to do is to slow down (i.e., by easing off the throttle and perhaps even jumping onto the brakes), and this sort of action will shift a car strongly towards oversteer (translation: "Your honour, the plaintiff's husband drove around the corner, and the car just went out of control!! Clearly the defendant has placed a dangerously defective product on the marketplace, and in recompense for my client's mental anguish and lost future economic support, not to mention the suffering of her children who must now grow up without a father, the defendant must pay at minimum $2.4 million in damages..."). To keep a car stable under these situations, one normally has to build in enough intrinsic understeer to keep oversteer from developing at all; even there, a dedicated fool can still accidentally invoke oversteer for a brief time, but said fool will usually be subsequently saved by the car's stability when he completely abandons any attempt at controlling the car.

[Peter, can you find that Vortex post we put up this year, the one where we cut & pasted a Brake Forum post from a fellow who was saved by understeer, but who thought it was his driving skill?]


IMPLICATIONS

How does the above affect us with our VWs? Well there are a few salient points to keep in mind:

1) Our cars are not designed to be race cars, and they have been given a lot of understeer. This understeer exists so that ordinary people can drive these cars without much fear of spinning in normal traffic situations. If we take away this understeer, we reduce our safety margin. For the non-racers amongst us, this reduction is not a good idea -- particularly since (as we will eventually get to, sometime in the next few weeks) most people who think they want to reduce understeer would probably be happy with increasing steering response and agility, while leaving understeer unchanged.

If there are any under-24 males reading these lines, I can guess what many of you will be thinking! You'll be thinking "A safety margin is well and good for the soccer moms of the world, but I can get by with less, 'cause I'm a better-than-average driver, with faster reflexes, more experience (Hey, I've AUTOCROSSED!!), and I'll be focusing on my driving, instead of talking on a cell phone with my brain half dead, etc., etc., etc....". And for you folks who think this way, well, how can I phrase this? .... Let's just say that I was an under-24 male once, and I thought exactly that way....and I was completely wrong! If you haven't done a lot of driving at near-race speeds on a race track, in a race car, you might be better-than-average, you might have faster reflexes, and you might be better focused -- but in terms of your critical automatic-responses in a road emergency (i.e., what your hands and feet will do without your thinking about it), you're not much better off than the cellphone-talking soccer mom when Something Bad suddenly happens. No, I don't expect you to listen to me on this! (anymore than I listened to people saying the same thing -- it comes with being Young and Male), but maybe a girlfriend or Mom or somebody will read these lines over your shoulder; in any case, do please leave the understeer in place, unless you really have a reason to reduce it!

2) One thing the aftermarket shares with the OEM manufacturers is a strong desire to not be sued out of existence by the heirs and executors of deceased former customers. As a result, many if not most of the "performance handling" modifications out there do not reduce understeer very much at all; indeed, many of them actually increase it. Mods in this (enormous) category include (and we'll explain why & how in a later installment):

A) "Sport springs" that drop the car onto front bumpstops.
B) "Sport dampers" that degrade front roadholding while increasing darter-like agility
C) "Sport Low-Profile Tires" that are more camber-sensitive than stock

Items like the above will sometimes even slow a car's laptimes around a race track -- but they'll feel very "racy" (at least for certain people) while preserving or enhancing the stock understeer (which is good, as it keeps the paying customers alive).

(Note: there are mods that DO reduce understeer (one of them almost got Peter killed on a mountain road), and we'll discuss them eventually!)

3) And finally (at least for this installment, as it's getting late): since cars in general are so sensitive to weight transfer, and weight transfer is so easy to invoke (rightly or wrongly), an investment in a good driving course (or sometimes even in a good driving book -- a printed non-internet one!) is in many ways the most effective way of reducing or eliminating understeer. Case in point: during my own darter phase, I thought the ability to zig zag violently down a straight road, on a steady throttle, at fairly high speed, was the mark of an excellent car -- and it took me 2 years and much money & scraped knuckles to turn my poor little MGB into a car that could do that. It was only then that I learned that this much-modified car was now a frightful pig, and that I could get an equally incisive corner-entry turn-in with a completely stock MGB -- with much better overall handling characteristics -- simply by trail-braking a little at the beginning of the curve.

(And in passing, I guess that's why Peter and I are trying to write this thread: we both (independently) wasted a lot of time and money pursuing handling chimeras (and we both independently spun off into the weeds before we figured out what we were up to), and it'd be nice if we could save some of you some of our troubles!)

Ok, that's all for now -- Peter will likely cut & paste a bit, and then we'll resume next week or month. Cheers again!

- Ceilidh
Ceilidh is offline   Reply With Quote
Old March 27th, 2006, 21:43   #14
peter pyce
Veteran Member
 
Join Date: Nov 2001
Default

Quote:
Originally Posted by Ceilidh
..... Peter, can you find that Vortex post we put up this year, the one where we cut & pasted a Brake Forum post from a fellow who was saved by understeer, but who thought it was his driving skill? ......
Oh, that was one of the greatest! I have it bookmarked

Here it is, yours all the way to the end:

Quote:
It's been raining for a long time here in CT, but this is the first time this has happened. Coming home today I was going around a corner and saw traffic ahead.. I lightly applied the brakes, and immediately started fishtailing.. Almost hit the car to my left, then came back around as I countersteered.. Almost hit a telephone pole to the right as my rear end surfed up along the curb.. I was able to let up on the brakes and straighten her out just in time.. Thank god for autoxing and learning what to do in such situations.. Otherwise I would've surely wrecked.
Now for the questions:
- I know our brakes are rear biased, but why would the front ABS engage without the rear?? I felt the pedal pulsating so I initially thought I would be able to ride it out with the ABS, but the longer I braked the more I was losing control...
- What can be done to counteract the rearward bias?? Different pads front and rear?? What do you guys use??
(Or, in translation (and I'm afraid I'm going to be a little mean here, but it's unlikely that this person follows the suspension forum, and it's important to see what the VW engineers have to design for):

Quote:
"While driving faster than conditions permit and attacking a corner blind, I jumped off the throttle and then hit the brakes in the middle of the corner while my tires were loaded by lateral g's, causing a massive forward weight transfer and generating sudden oversteer. After overcorrecting and almost spinning back the opposite way, I was saved by my rear wheels hitting the curb, before it occurred to me to let up off the brakes. Upon straightening the wheel, I then let the car's natural dynamic stability restore things to equilibrium, after which I congratulated myself on my driving prowess and then blamed the car."
For the people on the suspension forum, it's hard to believe that people can drive this way and expect the car to not spin, but that's exactly what the VW engineers have to cope with. Were our cars a little more neutral, the person making the above post would probably be dead now. And if we add to the scenario a car heavily laden with 900 lbs of family and kid stuff in the back, with random tire pressures and a little bit of winter ice, we can maybe forgive an engineer from thinking, Hmmm, perhaps I'm going to give this car lots and lots of understeer at high cornering loads...
peter pyce is offline   Reply With Quote
Old March 27th, 2006, 22:03   #15
compu_85
Gadget Guy
 
compu_85's Avatar
 
Join Date: Sep 2003
Location: Springfield VA
Default

I tell ya what, you lean so much here on TDIClub. I'll defintally be folowing this thread!

-Jason
__________________
Present:
2018 Tesla Model 3 DM. 3500 miles.
2014 Cadillac ELR. 33,000 miles.
2013 Fiat 500e. 33,000 miles.
99.5 Jetta "GLX" TDI. 323,000 miles. Power Memory Seats, HIDs 11mm pump, BV39 Turbo, RCIII 36/47 MPG.
1991 Mercedes 350SDL 230,000 miles, 70,000 on engine. 18/27 MPG.
Past:
2012 Passat SE TDI DSG. 114,000 miles. LED tails, Memory Seat, HIDs. Bought back by VW.
2004 Touareg V10 TDI. 165,000 miles. Sold to Matt98AHU w/ flat camshafts.
1988 Audi 5000S Quattro, 1992 Jetta ECOdiesel, 1991 Jetta ECOdiesel.
Thank you for giving me the BUG*PWR award. It means a lot to me!

Check out the official TDIClub Chat Room!
Quote:
Originally Posted by BRUSSELS BELGIAN View Post
Maybe I should pay MYSELF to do bad work on my car!
compu_85 is online now   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -7. The time now is 08:39.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright - TDIClub Online LTD - 2017
Contact Us | Privacy Statement | Forum Rules | Disclaimer
TDIClub Online Ltd (TDIClub.com) is not affiliated with the VWoA or VWAG and is supported by contributions from viewers like you.
1996 - 2017, All Rights Reserved
Page generated in 0.22206 seconds with 9 queries
[Output: 162.16 Kb. compressed to 140.59 Kb. by saving 21.57 Kb. (13.30%)]