Storz

This summer I am planning on autocrossing the vette a lot. With the little bit of hard low speed driving I have done so far I noticed that the car tends to push the front end pretty bad, I am guessing this has to do with the cars 30mm front and 22mm rear sway bars, what I am hoping the more experianced autocrossers here can help me with is whether or not to get a larger rear sway bar to neutralize the cars handling a bit, and get rid of that intial push, I know from autocrossing my previous car, a Cavalier Z24 that understeer is horrible on an autocross course, or of anything else that can be done to get rid of that push? Thanks in advance for any advice.

SWCDuke

Production cars are set up with inherent understeer to keep them stable, which can be a disadvantage in autocross. Try increasing the front negative camber and adding a little front toe-out first. If that doesn't work, a bigger rear bar or smaller front bar, or some combination of both will reduce understeer more, but you can get to the point where the car is unstable if you push it hard in normal driving. Finding an acceptable balance between low speed understeer and high speed oversteer is often the focus of race team chassis engineers, particularly on street courses that can combine tight hairpin turns with high speed sweepers.

Duke

Bill Dearborn

The Vette is still going to push in most low speed autocrosses. The turns in a lot of the courses I have run are just too sharp to go around without pushing. I usually try to enter them slow enough to avoid pushing at the beginning of the turn and then getting on the throttle more once the car has started rotating and is approaching the apex.

I have modified the camber, tire pressure and played with the toe. You are only talking minor differences in handling on these courses. The most benefit you will get is by slowing your entry speed, brake very hard to get the speed down but make sure your foot is off the brake and over the gas pedal when you start to turn the wheel. Once you get that down then the other mods will give you a better time.
Bill

corvette dave

Storz,
If you are going to make changes to the car you always work to improve the end (front in this case) of the car that is not performing. If you put a smaller bar in the front you will probably reduce the grip in the rear. That may help your problem but will probably give the car less grip overall.
I would try a larger bar in the rear first and/or the alignment changes that were mentioned in a previous post.
As said in other posts you can change you driving style. If you get off the brakes just before you begin your turn, the weight will transfer to the rear, decrease in the front, increasing the understeer. Staying on the brakes a little while turning will help keep more weight on the front tires resulting in more grip. (trailbraking)
I have tried both fixes, bar and driving style, with success. Mostly on road courses which I consider somewhat similar.
Dave

Allthrottleandsomebottle

And now a good list of starting point ideas...............Much easier written than done Just like any other sport.....lots of variables
I am not claiming this list, this is just some possibilities and I have had to deal with some of them!


OVERSTEER / UNDERSTEER CORRECTIONS LIST

Understeer Corrections

Push, plowing, front tires slide out first
Usually slight understeer is safer
Raise front tire pressure
Lower rear tire pressure
Soften front shocks. Stiffen Bump
Stiffen rear shocks
Lower front end
Raise rear end
Widen front track
Install shorter front tires
Install taller rear tires
Install wider front tires
Install narrower rear tires.
Soften front sway bar.
Stiffen rear sway bar.
More front toe out.
Reduce rear toe in slightly.
Increase front negative camber.
Increase positive caster.
Soften front springs.
Stiffen rear springs.
May need more front suspension travel.
Install wider front wheels.
Use softer front compound if possible.
Use harder rear compound if possible.
Remove weight from front of vehicle.
Add weight to rear of vehicle.
Drive a different line.
Use weight transfer to your advantage.
High Speed. Increase front wing downforce.
Too much front brake.
Vehicle is TWITCHY at limit and hard to keep
ahead of in the steering department.
Lower front and rear tire pressures slightly.
Suspension may be too stiff.
Shocks may be set too firm.
Tires may be old or hard.
Vehicle may not have enough suspension travel.
Vehicle may have a toe problem front or rear.
Increase negative camber front and rear if possible.

Oversteer Corrections
Loose, rear tires slide out first.
Oversteer can be dangerous, especially at high speeds
Lower front tire pressure.
Raise rear tire pressure.
Stiffen front shocks.
Soften rear shocks.
Raise front end.
Lower rear end.
Reduce rear track.
Install taller front tires.
Install shorter rear tires.
Install narrower front tires.
Install wider rear tires.
Stiffen front sway bar.
Soften rear sway bar.
More front toe in.
Increase rear toe in.
Reduce front negative camber.
Reduce positive caster.
Stiffen front springs.
Soften rear springs.
May need more rear suspension travel.
Install wider rear wheels.
Use harder front compound if possible.
Use softer rear compound if possible.
Add weight to front of vehicle.
Remove weight from rear of vehicle.
Driver may be going in too deep.
Driver may be getting on the throttle to early.
High Speed. Increase rear wing downforce.
Too much rear brake.
Vehicle slides and is easy to drive at limit but does not corner to full potential.
Raise front and rear tire pressures slightly.
Suspension may be too soft.
Shocks may be too soft.
Roll centers may be too high.
Lower vehicle.
Tires may be too hard.
Widen track front & rear.

A properly set up vehicle will usually push slightly on corner entry, be fairly neutral at the apex (STEADY STATE) and exhibit slight power oversteer on corner exit. Tight courses may require more oversteer, fast tracks understeer.

Items needed: Accurate tire pyrometer, tire gauge, notebook and tape measure. Suspension information books.

Note: This is a sample of the methods used to correct various handling problems. Books have been written on this subject. Not every correction will always work as expected. Stiffer front sway bars will, in many cases, decrease understeer because of reduced body roll and better camber control. The best rule is to change only one thing at a time and keep notes

Storz

Thanks for all of the great responses :cheers: I know that working on my technique is the first and best thing to do in order to get faster, and I am taking an autocross school at the beginning of April. However I am trying to get as much information as I can before I start. This forum is great tho and I have say that I've learned a ton from reading some of the posts lately, especially the heel/toe thread and the one about camber settings. Thanks again

VetteDrmr

Storz,

I think one of the main reasons stock C5s understeer as much as they do is the difference in tire size front to rear, 275s in back, 245s in front. I've gone to 275s in front, and my understeer is virtually gone, although I haven't had them long enough to learn how to best drive them yet. It definitely takes a new technique.

Hope this helps,
Mike

Storz

Interesting, but my car has the same size 255/50/16s all the way around.

VetteDrmr

Oops, I should have caught that from your sig. :bb Sorry.

Storz

:lol: No big deal...maybe I need to put some space saver tires on the rear and 315s on the front :lol:

Bill Dearborn

As you can see from the list above there are a lot of things that you can do. The most important thing is to get the car around as fast as you can with the normal street set up. Once you know how to do this and how the car feels you can start on the remainder of that list in the endless search for perfection. Before I ran a C5 I ran an 86. The 86 understeered much more than the C5 does. With the stock setup the C4 is a very stable car that takes a lot to get it to oversteer, while the C5 is a car that has a tendency to oversteer. When I first switched my description of the C5 was Tail Happy. Once you get so you can manage the understeer you will find that you can really get a C4 around a low speed autocross course as Roger Johnson proved for a number of years with his 86.
Bill

Storz

Thanks :D

JSA 007

:iagree: You really have to slow the car down before the turn to get the line right. Once you're locked-in, then you add some gas. :) If you go too fast then trailbraking is a good idea. Also, if you go too slow, there's throttle-induced oversteer.

Good luck and always practice :cool: