WICKEDFRC

After some research.....

Understeer is caused by an unbalance in the car straight from factory to assist "bad drivers". Hahahaha Adding bigger (oversized) front sway bars add to the problem of understeer (even though bigger sway bars significantly reduce roll.)

Compensating for understeer requires going with a bigger rear sway bar, or, a smaller front sway bar.

Quoted from link source:
"As an extra data point, I talked to SCCA Solo II champ Gary Thomason about his car, and he said that he tried the T1's, and that the car understeered horribly, and that the front bar was simply too big."

Given this statement, I came up with the following madness.....

Base C5 Sways
23mm / 19.1mm = 3.9mm difference

C5 Z06 Sways
30mm / 23.6mm = 6.4mm difference

Hotchkis Sways
31.75mm / 25.4mm = 6.35mm difference

Last Set up I had:
35mm / 26mm = 9mm difference

Current Set up I have (T1)
38.4mm / 27.5mm = 10.9mm difference

My analysis: While the base was the closest ratio (3.9mm difference), many said the C5 Z06 sways were a significant upgrade over the base sway bars (+7mm Front / +4.5mm Rear over base using C5 Z06 Sway Bars). Then, along came Hotchkis.

While Hotchkis only added +1.75mm front over C5 Z06, Hotchkis added +1.8mm to the rear (which was more mm than it added to their front) and emerged with less overall mm difference than the C5 Z06 over the base at 6.35mm vs C5 Z06 with 6.4mm.

Jumping to the T1, it placed a huge margin of possible understeer error on a street C5 with 10.9mm difference! If many say the Hotchkiss was an excellent upgrade over the C5 Z06 sway bars, my conclusion would be to minimize the huge margin of possible error of the T1 "front to rear" difference of 10.9mm.

To do this without affecting oversteer, I would replace the FRONT sway bar with a smaller bar, such as front Hotchkiss (31.75mm) to close the T1 gap down from 10.9mm to 4.25mm. (This would be using the Hotchkis Front Sway Bar and beefier T1 Rear Sway Bar).

If I went with a C5 Z06 front bar at 30mm, and the T1 Rear Sway Bar at 27.5mm, this would further close the gap down to a mere 2.5mm difference from front to rear.

So, am I up too late trying to think too much into it, or could this be a valid perspective to consider for my steering issues?

In addition, since I have my HAL QA-1s set up on 10 all around, will reducing the front shocks to 5 have anything to do with understeer?

Thanks all. Hopefully the experts will chime in and put their spin on this theory.

WICKEDFRC

ps....Thanks to Mike (Short-Throw), he provided this useful link in my quest for knowledge. I believe it is a valuable tool for anyone looking to gain more knowledge from those who have spent countless hours perfecting their set up.

Thanks Mike!

http://www.nyracer.com/overunder.htm

Solofast

First of all you have to remember that actual stiffness of a bar is a cube of the diameter, so a small change in diameter is a big change in bar stiffness. Also bars act in conjunction with springs so they don't provide all of the roll stiffness, so big change in bar stiffness isn't everything that is going on here. You can't look a the difference from each other, you need to look at the difference from stock. If you look at the Pfadt sway bar graph that is on their site you will get a better idea of the relative stiffness. Here is a link to a thread that has the graph in it.

http://forums.corvetteforum.com/c5-z...rs-shocks.html

Remember that Gary was talking about an SCCA stock class car. In stock in those days you could only change the front bar. So what he was saying is that the Z06, with the stock springs and bars was well balanced and if you added any front roll stiffness it would make the car push. I agree with that. I tried poly front bushings when I first started to set my car up and it pushed, I can't imagine how much of a pig it would be with a T1 front bar and a stock rear bar, so he is correct.

If you go much bigger in the front you are going to have to increase the rear roll stiffness to keep the car balanced. Unfortunately, you can't change both bars and stay in stock class, if you are going to street prepared that's a whole new ball game and you will need huge bars on both ends of the car along with bigger springs.

Shocks tune the transient response, bars and springs tune the steady state handling. If the car is pushing or loose everywhere, or just in mid corner then you need to change the bars. If it is doing it just on corner entry or on corner exit it is a shock issue.

Lastly if you are serious about autocross you need to get rid of the QA-1's and get a set of Koni's or other serious shocks. I don't see anybody winning any national championships on QA-1's so I will leave it at that.

Lastly, you need to go to the Far North Racing site and spend an evening reading Dennis Grant's information on car setup and shock tuning. You will learn a lot about what works and why. Suggest you start here.

http://farnorthracing.com/autocross_secrets18.html

WICKEDFRC

Thank you Solofast! Very well said and I appreciate your knowledge and input.

abflyboy

OMGosh it's good to know I'm not the only one thinking about this stuff in lieu of sleep ...

Bill Dearborn

Although the C5 will understeer if you drive hard into a corner it will also oversteer if you come off throttle. It is a naturally tail happy car under trailing throttle conditions and will tighten into a turn very easily. You can lift off the throttle to get it rotating and then push back down to reduce the oversteer to keep from spinning. Once pointed where you want it you need to add more throttle to keep the rear planted.

It is hard to see this at first in autocross situations but if you are on a road course you can really feel the car tighten into a turn when you lift off the throttle and how playing with the throttle changes the yaw in the turn. When I autocrossed the car I did the same things just much quicker. Never ran at the National Level but I did get a lot of FTDs running in my region.

Bill

AU N EGL

Under-steer? I have never had that problem when I put on the appropriate tire sizes and a fair amount of negative camber.

When I ran 285s up front the car had under steer like crazy, then when I put the 305s or 315s and -2.0* camber up front under steer was gone.

corners like it is on rails, even with cold tires.

as Bill mentions This is a great way to steer the car when you have too or with very tight corners, Point and shoot.

betelgeuse

Doesn't rear toe also affect understeer/oversteer?
Too much (rear) toe in = understeer.
Too much (rear) toe out = oversteer.

Greg

Solofast

Well, yes it does, but rear toe effects roll steer more than basic understeer/oversteer as well as turn in as well as having a big effect on power on/off steer effects.

Some FWD cars use toe out in the back to help the car rotate.

IN NO CASE DO YOU EVER WANT REAR TOE OUT ON THESE CARS.

Optimal setup is just a bit (like 1/8 of an inch) of rear toe in. THEN you can work your setup from there. There have been some that have used big amounts of rear to in to tame some Z06 oversteer problems. Part of that was that these guys had lowered their rear too much and were bottoming out. Using big (like a 1/2 inch) of rear toe in "fixed" the problem that was actually the rear bump stop causing oversteer. Since the people setting up these cars realized what was actually happening nobody who is fast is using big rear toe in numbers.

betelgeuse

Yes. That's what I thought but on this forum when I was looking for a good track alignment some people were running or recommended toe out for the rear. Like Pfadt Racing calls for negative (-) rear toe.
http://www.pfadtracing.com/blog/wp-c...-9.12.2011.pdf
Maybe it's just a typo.
I've been tracking a BMW and I always ran 1/8" toe out in the front and 1/8" toe in at the rear. When I saw the Pfadt Racing recommendations I figured it was maybe because of the differences of the two suspensions.

Greg

AU N EGL

1/8" toe is quite a bit.

0 to 1/32" for high speed tracks,

1/16" for short tight tracks

I agree with solo, if you want understeer, put on some rear toe OUT. ( turn you Mother F er TURN ) and it just goes straight.

betelgeuse

Ummmmm. That's not what Solo said.

He said; "Optimal setup is just a bit (like 1/8 of an inch) of rear toe in...... There have been some that have used big amounts of rear to in to tame some Z06 oversteer problems.........Using big (like a 1/2 inch) of rear toe in "fixed" the problem......"

You're saying the opposite. I think you guys are just trying to confuse me

Greg

WICKEDFRC

Revisiting this thread, is there a recommended street set up that will tighten up steering responsiveness without compromising overall even wear on the tires?

Just looking to start somewhere when I go for an alignment. Thanks!!

PS: If you know all the specifics, please post, such as

FRONT
Caster Stock
TOE -2
CAMBER Stock

REAR
Caster Stock
Toe Stock
Camber Stock

Lothar34

Not really. Anything you do to increase responsiveness works to the detriment of tire life.