When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Adjust ride height when going to Square set up on C5Z?
I gather that C5s have built in rake, some of it based on suspension adjustment and some based on tire sizes. OTOH, I like using a square set up for various reasons and wonder when the tire sizes become the same front to back, if I should raise the rear (or lower the front) to replace the OE rake or is it worth it?
I'm in to hear ideas and thoughts as well. I have a square track setup and have the stock stagger wheel setup for street. I set my ride height/alignment with the track setup, so when I go back to the street setup, it was super rake and scrapes on just about everything. Other way around seems like a better idea from that perspective but would effectively remove all rake when I put the square tires on.
Corner balance the car, that is more important than rake.
I'm curious what your justification for that is. By corner balance do you mean set your cross weights to 50%? Pretty sure you can do that with a variety of rake settings.
As to OP, the STU autocross C5's run square setups and we all seem to be leaning towards ~ zero rake. I understand that for road course work a higher rake setting is recommended to reduce front end lift, however.
The under car air management and cooling is improved with the front slightly lower than the rear. That would be the only advantage I can think of to maintaining rake angle. I run a square tire setup for the track and did not reset the ride height to account for that. I already run into ground clearance issues as it is, no way was I going to drop the front any lower. I have my car setup to minimize bump steer and keep the suspension geometry where it was designed to function.
Like Crimlwc6 says I'd be more concerned with corner balancing than rake angle on a what is basically a tracked street car.
From a stock tire stand point there is only about a half inch of rake from front to rear. Stock diameter is 25.6 Front and 26.7 Rear. Or 1.1 inches diameter difference with the difference in ride height being half that or .55 inches. Not worth trying to correct if you decide to run equal diameter front and rear tires. Setup doesn't need to be square to get equal diameters. 275/40/17 and 315/35/17 are the same diameter. That used to be the popular track tire size in the early C5 days.
When we raced PTA (basically a no-aero stock C5 setup on 275s) we would keep about 5/8" of rake in the setup to help stabilize the car in the 135-150mph range.
As crimlwC6 stated, the corner balance setup is actually more important. We would start with the static rake, then corner balance the car as close as we could get with stock leafs and spring adjusters, and let the rake fall where it fell after the adjustments.
When we raced PTA (basically a no-aero stock C5 setup on 275s) we would keep about 5/8" of rake in the setup to help stabilize the car in the 135-150mph range.
As crimlwC6 stated, the corner balance setup is actually more important. We would start with the static rake, then corner balance the car as close as we could get with stock leafs and spring adjusters, and let the rake fall where it fell after the adjustments.
Do you "keep about 5/8" of rake" from the stock staggered setup or after going to a square set up? If it was the staggered set up then what sort of rake did you end up with after corner weighting and a square set up?
You are over-thinking this. Put your square setup of wheels and tires on the car, set the front ride height where you want it for suspension compression to not eat up your fender wells, put 5/8" rake in the rear spring, then corner balance, and go drive the $h!t out of it.
The ONLY real place that the rake helped my car was topping the hill on the back straight of VIR. With a little bit of rake, it helped give the car a hair more natural downforce and the rear of the car would not "float" as much cresting that rise at 135+. Anywhere else, I didn't notice the rake helping anything. If the car gets tail-happy under braking, then you know you have too much rake and you are transferring too much weight onto the front. So you raise the front a hair or lower the rear a hair.
Do you "keep about 5/8" of rake" from the stock staggered setup or after going to a square set up? If it was the staggered set up then what sort of rake did you end up with after corner weighting and a square set up?
... and doesn't lowering the front screw up bump steer?
Corner balance the car, that is more important than rake.
Exactly- corner balance the car and then align and then corner balance again. Yes, corner balance, 50% cross weights. The quick answer why is that you want maximum m grip on all four tires when turning left and right like we do on a road course or autox. Most likely you will have some positive rake anyway. Then, it comes down to testing and taking tire temps. Whatever course you run you want the temps at all four corners as close as possible.
You are over-thinking this. Put your square setup of wheels and tires on the car, set the front ride height where you want it for suspension compression to not eat up your fender wells, put 5/8" rake in the rear spring, then corner balance, and go drive the $h!t out of it.
.
Thank you. This does answer my original question concerning re- establishing rake and which end to do it at.
BTW, do you measure the rake from the jacking points or the lower control arm mounting points?
Agree completely that corner weighting is important, just didn't know how important rake was. ( I sometimes wonder if putting more weight on the right side of the car for clockwise tracks and on the left side of the car for counterclockwise tracks might be worthwhile something like the roundyround guys do. OTOH the losses on Left hand turns might be worse than the gains on Right hand turns, i.e a problem those guys don't have to deal with)
Last edited by Soloontario; 11-08-2017 at 12:38 PM.
Thank you. This does answer my original question concerning re- establishing rake and which end to do it at.
BTW, do you measure the rake from the jacking points or the lower control arm mounting points?
Agree completely that corner weighting is important, just didn't know how important rake was. ( I sometimes wonder if putting more weight on the right side of the car for clockwise tracks and on the left side of the car for counterclockwise tracks might be worthwhile something like the roundyround guys do. OTOH the losses on Left hand turns might be worse than the gains on Right hand turns, i.e a problem those guys don't have to deal with)
Generally the jacking points is where we measured. Although, after years of racing and the car being on and off jack stands countless times, my jacking points are badly bent and mangled. So pay attention to what surface you are using.
We (the C5 Mafia) have had the "more side weight for this track" discussion for years and never proved anything with any of our bench racing.
Stock Rake is 5mm or 1/4 inch. 6" front, 6.22 rear, as measured by the jack points
My C5 Z06 came with Pfadt Featherlight coilovers. The car had previously been tracked, and my intent is the same The stance was very low, 4.25" from the jack points, basically flat. He was running a 305 square setup. That was too low for me and I wanted to put some rake in as most opinions favored that for high speed stability. I'm running a 18" square tire set up. I started by raising the front to 5", measured from the front of the front jack point. At that point I had to really jack the *** end up almost as high as the rear coilovers would go to get any rake. The best I could come up with was 4.75 from the front of the front jack points and 4.875 from the rear of the back jack points. I then got an alignment. Next spring my intent is to get it corner balanced and see where that takes it. I bought one of these, indispensable tool for ride height adjustments.
SoloOntario,
I see no one asked the most important question; what will you be doing with the car? Being this is in the "autocross Road course" section, I am assuming it's one of those. Perhaps your name says it all, solo.
Regarding rake, street, what ever looks best. Autocross, I don't think rake matters, but if you want to be Nationals" competitive, My guess is everything matters at that level. Road course, my opinion is rake matters at high speed but probably matters less if you have a vented hood.
My
Once I have my corner balance completed, I'll post ride height by corner, but that won't be till spring.
11-05-2017, 11:46 AM
Adjust ride height when going to Square set up on C5Z?
