Mojave

My '96 is very twitchy all the time, it won't plant the power and it's very loose on throttle lift. I'd love to know the secret to getting some rear grip.

ZR1 MK

Ill try and do a write-up and post it when Im done. I type too slow and theres plenty of info to tell.

ZR1 MK

My write-up will help, but in the mean time. Autocross or track? Are you using the stock trailing brackets? Whats your set-up? I rememeber looking at your website during the car build, but dont remember all the details.

Kubs

FWIW I use -1* chamber and 1/8" total toe IN in the rear of mine. I have actually been chasing an understeer problem which I think I have narrowed down to the rear sway bar. Since my car is a Z51 it is supposed to have a 26mm bar in the rear but mine measures 22mm. Randy at DRM says GM used to throw any old bar they had sitting around on it regardless of what it was supposed to have. I dont know what size bars you have but with my experience in settings I have tried, not having enough toe, or too much chamber will make the rear twichy. I bought a tire probe to measure the temps of my tires. When I got to a setting that had even temps across the tire (measure inside, middle and outside) I left it and it seemed to handle the best as well.

BrianCunningham

They weren't running any kind of aero, let alone a splitter at the front.

ZR1 MK

I run 2.0 left and 1.8 right camber on the front with .75 on the rear. I got exact temps across my left front once in all my years and consider that amazing.

Mojave

I run both, but lately auto-x (need to get back to the track).

3200 lbs full of gas with driver
DRM coil overs, 500 lbs front, 275 lbs rear
30 mm front bar, 24 mm rear, with heim end links
front: -2.3 camber, 6.8 caster, .15 degree toe out
rear: -.7 camber, .08 degree toe in
DRM trailing arm and camber brackets
heim trailing arms and camber rods
fresh factory toe rod ends
fresh u-joints and wheel bearings
315's on all 4 corners (hopefully soon to be 335's).

66IISS

Mojave,

What are your corner weights / ride height? I remember you doing extensive weight reduction, could it be that your weights are off?

RedLS1GTO

Well... here is the update after VIR Mon and Tues.

I still think that the car needs some rear downforce to equal out the front. However, the amount that it needs really isn't all that much. I have also come to the conclusion that the problem I am having with the tail is a combo of 3 (or more) things. First, I think I am running a pad in the rear that is too aggressive. Second, The reason that the pad is too aggressive is the fact that it is unbalanced with the downforce (even a small amount) in the front and nothing in the rear. Finally, I need to run better tires. I was on (bought used) Kuhmo V710s on a relatively cold track and I really struggled with traction on all 4 corners way more than I ever have in the past.

In the end, even being a little slick, I was still turning laps that were right on par with a few of the guys in the C6 Z06s that were there and faster than the C5s so I can't complain too much. All said, I am to the point of making small changes to get the car exactly how I like it rather than big ones so it was a pretty good first year in the car. I am going to think about it for a while and put that expensive engineering degree to work and see what I can come up with. I do appreciate all of the help so far from you guys!

abc 123

http://forums.corvetteforum.com/c4-z...-diffuser.html

ZR1 MK

Rear springs are a bit soft.

If you running a lowered rear and the stock toe rods, you probably get more toe change than the .08 neg you have and are going toe out as the suspension travels. This gives you a switchy and oversteer condition.

I hope you changed the Bilstein front lower shock bushing. I have a write-up on this.

DRM trailing brackets with soft springs at low speeds is a definite "plant the power" problem.

shakedown067

THANKS!

Kubs

Mine are never exact like you said but are within 5-7* from highest to lowest temp.

I agree with you that more toe in the rear of a lowered C4 really helps. People say that it will wear the street tires too quickly but so far it seems to be really even. The tire moves out under compression more than you would think. The bump steer on the back of C4s is bad.

Aardwolf

Banski was talking about a fix for that coming soon last I heard.

Mojave

Thanks for the ideas. The DRM shocks came with poly bushings. If that is the wrong bushing, what is the right one?

How do the DRM trailing arm brackets hurt rear forward bite? I thought they were supposed to help. I was hesitant to go too stiff in the rear so it would plant the power better. Is there any fix for the rear bump steer other than stiff springs?

Kubs

ZR1 MK

Im half done with my write-up. Its getting large.
Ill be posting a new thread with it, but Ill put the link here too.

rfn026

I've got an article on C4 rear suspension in this month's Corvette Fever. You can find the same thing (sort of) on my site.

This article talks about the Rippie brackets and the various types of poly bushings. I figure I might as well add to the confusion here.

Richard Newton
Race Cars 360

ZR1 MK

Some good info. I like the pictures as part of the article.
My write-up wont have pics, but will have plenty of tech stuff.

Mojave
Regarding shock bushing, I meant the lower bushings.

Mike

Kubs

I am looking forward to reading your write-up!