BUSTED!: Two front-wheel-drive setup myths.

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1) Less front roll stiffness and/or more rear roll stiffness makes a car understeer less.

Actually, if you allowed me only one bar, I'd take a front upgrade over a rear. It'll make the car faster.

If you have a car where all four tires are working like they were designed, yes. This is not the case if you have any tire off the ground or any tire cornering with a bad camber angle. With our struts, their limited caster, and the soft suspensions and moderate alignments most people run, this is never the case. This car has twice as much weight on the poor front tires, and you MUST work with them until they're fairly happy before you can do anything else. Stiffening the rear will reduce front weight transfer - up the the point where the inside rear is unweighted. If you lift the inside rear half an inch, you have more than enough rear-bias in your roll stiffness. Any more will make you SLOWER. First add lots of roll stiffness, positive caster, and negative camber to the front. If you do enough of that, you can manage to keep the front tires flat on the ground and you can begin really tuning. THEN, and only then, add rear roll stiffness, and only add it until the car is balanced to your liking or you start lifting a wheel.

2) Rotation is good - we want the rear loose.

We want less understeer. Adding oversteer is not the way to get it.

Do the front tires care if the rear tires have 10psi or 100psi in them? No, of course they have the same amount of grip either way. Do they care how much camber the rear has? No! Trying to reduce understeer by getting rid of rear camber (happens more on Civics, not Contours), running smaller tires, or jacking tire pressures way up is dumb. Adding roll stiffness is good because it hurts rear grip but (if you have good chassis stiffness, which we do) it helps the front, which is the real key. Again, see #1 for how to do that right.

So why not balance the car by making it rotate when we want? You're going to be slower! The fronts are the limiting factor. When you drive a Contour you need to think about the fronts and the fronts alone. If you make the rears break loose at about the same time as the fronts, the car will feel balanced. But, we know that sliding isn't fast - we want to stay under the tire's limits, not Toyko Drift around the course. So why make yourself fight the front AND the rear? I actually prefer to soften the rear pressures until they're at maximum grip. This helps for two reasons - a) I can drive harder without worrying about spins, and I can concentrate on the front tires alone and b) the soft sidewalls flex more, and give a higher slip angle while maintaing traction. This means I get rotation (and get the back tire away from the apex cones) without giving up grip.


Bonus: Good on the street and good on the track are very different things. It helps to have a car that feels good on the track/autocross course so you're comfortable. But really, you make the car as fast as possible and still be driveable. This may mean it plows like mad at the limit - so what? If that's the fast setup, do it! You make the car fast, and adapt as a driver. I've been driving an F Mod Formula 440, and it handles like crap. It's not responsive or intuitive at all - but if you drive it right, as painful as it might be, it's fast.

 

[Kremithefrog]

I hate driving right :troutslap:, but good tips.

 

[rkneeshaw]

Just the article we need around here, very good writeup, thank you

 

[RogerB]

Whoops on the double-post!

 

[RogerB]

1) Less front roll stiffness and/or more rear roll stiffness makes a car understeer less.

Calling this a myth is wrong-headed. Front-rear steering balance is absolutely controlled, in part, by roll stiffness at each end of the car.

You actually make some very good points in this post, but calling this a myth isn't one of them.

The rest of item 1 is great.

2) Rotation is good - we want the rear loose.

We want less understeer. Adding oversteer is not the way to get it.

Now you have my attention, but your first supporting sentence doesn't make any sense. Understeer/oversteer are like yin and yang. You can't increase one without decreasing the other--by definition. The "perfect balance" is dependent upon car, driver, and intended use.

Now for the good stuff:

I think what you are really trying to say, (or should be), is that under/over balance is fine, but traction on the front end is more important, and should be addressed first.

I know a lot of people treat the handling balance as the be-all. You're saying it should be the second thing after traction, and since our cars are camber and traction-limited at the front, we never get to the point where we should worry about perfect balance. Just have to accept a little understeer, and drive within the traction circle.

I seem to recall the guys at GRM running into this with their SRT-4. Not much camber available in the front, so they continued to get understeer. They played around with narrower rear tires, weird pressures, positive camber at the rear. I can't remember the results, off hand, but in the end they gave up and retired it from autocross to be a track-day whore.

Certainly food for thought. I've got that SVT front bar in my garage, and knowing what a hassle it is to get on, I'm pretty much convinced I should skip it. Probably ought to do poly bushings up there, too, for good measure. For that matter, why screw around with a bigger rear bar?

 

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Calling this a myth is wrong-headed. Front-rear steering balance is absolutely controlled, in part, by roll stiffness at each end of the car.

You actually make some very good points in this post, but calling this a myth isn't one of them.

In a car like ours, the camber and weight issues overshadow the roll stiffness balance dramatically. Re-read what I said: once you meet the conditions I set forth when all tires are working like they should, then roll stiffness matters. It takes a huge amount of work to get a Contour to that point, and no one here but me runs a street alignment and spring rates high enough for them to matter much.

Let me phrase is another way - I called it a myth because most people consider that statement I called a myth to be universal. Most people will stare at you when you say they'll plow less with a bigger front bar. I'll go so far as to say nearly all stock strut-suspended cars will be faster, and understeer less, with a bigger front bar.

Now you have my attention, but your first supporting sentence doesn't make any sense. Understeer/oversteer are like yin and yang.

What I meant by that sentence was that reducing rear grip is not the way to go. But it does go beyond that - every car can understeer and oversteer. You can make the car oversteer with less prevocation, and still have the same understeer problem in some situations, maybe even make it worse. This car will be slower everywhere. A huge rear bar on stock suspension will do this on the autocross course. In a big skidpad the car understeers less, and most people would say I shifted the balance towards oversteer. But in situations where the car was having the worst understeer, it's now worse.

You can't increase one without decreasing the other--by definition. The "perfect balance" is dependent upon car, driver, and intended use.

You can make a car that will sometimes plow horribly and sometimes snap-oversteer, and then set up the same car to always plow, and then make it oversteer controllably and plow mildly - real tracks are not skidpads, and any car will have multiple f/r slip angle ratios on a course - even in the same turn.

I think what you are really trying to say, (or should be), is that under/over balance is fine, but traction on the front end is more important, and should be addressed first.

Well sort of - I'm saying balance may not be achievable, and may not be desireable. It might be faster to make a car that is NOT balanced.

Certainly food for thought. I've got that SVT front bar in my garage, and knowing what a hassle it is to get on, I'm pretty much convinced I should skip it. Probably ought to do poly bushings up there, too, for good measure. For that matter, why screw around with a bigger rear bar?

I'm convinced the SVT bar will make your car measureably slower than a bar that's bigger than stock by the same percentage. All except the most balanced cars with the best geometry are faster with a bigger bar up front.

 

[warmonger]

I'm learning here....Thanks!

But question, why did SVT see fit to lower the front and increase the rear bar stiffness?
Also, I'm having issues understanding what you mean by increasing the geometry. I'm no suspension setup guru but I want to learn....its one of my weak points in automotive. I haven't gone much beyond finding something that someone else did and works, like a ready built suspension and boxing my own rear subframe.

 

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But question, why did SVT see fit to lower the front and increase the rear bar stiffness?

I don't think they were concerned with ultimate performance. They probably wanted to limit wheelspin from the higher-power SVT engine and make the car feel better the way most people would drive it: on the street.

One thing I didn't mention: as tires get stickier, you need to get stiffer to keep the geometry in check. On junky all-seasons you might not generate enough grip, and thus body roll, to get up on the outside edge of the tire.

Also, I'm having issues understanding what you mean by increasing the geometry.

Not sure I follow you there. When I talk about geometry I mean the curves the suspension follows and the angles it makes the tire take, mostly the dynamic camber. My Miata gains negative camber in roll, which helps make up for the camber lost due to the roll. This is a good geometry. Our struts keep camber pretty much the same in roll, with only relatively small gains or losses, which is one of the downsides of a strut suspension. BMWs have tons of caster to give you camber as you turn the wheel, which is the other way to add camber in corners. We have very little.