A-Body Autocrossing

[Captain]

There's no doubt air shocks would be a bit crazy on an autocross car, but lots of times life is about playing the cards you're dealt...

UPDATE:

Ran short on money to upgrade the shocks before that weekends race, the only changes I made were psi in tires and air shocks. In my class (Street Mod Street Tire) I finished 10th out of 18. However, comparing my lap times to cars in other classes I beat: new (stock) Camaro RS/SS, Mustang GT, Cadillac CTSV and Challenger SRT8, Trans Am, C4 Vette. I was very happy with I ran this weekend. Remember the only real "upgrade" on the car that wasn't a factory option is the rear disc brakes and headers (even at that my disc kit is all off the shelf gm parts). The current rear air shocks and front drag shocks are probably a downgrade over an oem shock. Everything else is just new oem replacement parts.

Having said that, increasing psi in the rear air shocks is what helped me the most this weekend, on corner entry the car actually wanted to rotate and turn in, it didn't just lean on the front tires until they begged for mercy. Front end geometry is what is hurting me the most right now- I'm destroying my tires because they are rolling over on the sidewalls so far.

I have a camber gauge and shims- looking for some help on what kind of adjustments to make for track driving.

[UMI Tech]

Max out the camber as far negative as you can (put a bunch of shims in it). Depending on your tolerance for vague feeling steering, you can get more max camber if you sacrifice caster. On second thought, put a bunch of shims in the rear of each cross shaft and a moderate amount in the front of each cross shaft.

1/16" toe out will help turn-in but you'll have to "drive" the car since it will tend to not self cancel on corner exit.

If you're low bucking the end of the season, add some 1/2" taller ball joints. Rumor has it we are going to have some 0.9" taller in the upcoming weeks but maybe not in time for your race.

http://www.umiperformance.com/catalo...roducts_id=676

Adding ball joint height is a way to increase spindle height and help it gain camber.

ramey

Oh, and it sounds like you were driving well. Good job.

[Captain]

I have a gauge, so loading it up with shims is a little less scientific than I was hoping for. What kind of degrees should I be looking for?

[UMI Tech]

I'd choose around 2.25 degrees.

[Captain]

I'd choose around 2.25 degrees.

Wow, that's a lot of negative camber. I am chewing the **** out of the outer sidewall though.

[Captain]

To increase negative camber I'm going to add an equal number of shims to both mounting points on the upper control arm, right?

[UMI Tech]

Yup. Since the factory geometry doesn't allow for much negative camber gain (?!) we have to start with an aggressive static amount.

With the tall spindle and geometry upgrades we can run a tire wear friendly static alignment and still have the proper camber during cornering.

ramey

[Captain]

Static means wheel relative to ground, right? My camber gauge is one like this:

[UMI Tech]

Static means "car is not moving". Dynamic is how the camber changes when the suspension is traveling in compression or extension.

That may be the exact gauge we have. Nice choice.

[Hotchkis]

If you are looking for a complete suspension solution with proven results in autocross competitions then I would definitely suggest taking a look at our Stage 2 Total Vehicle System (TVS). It comes with absolutely everything needed to completely transform your A-Body with just bolt-on parts. Every part of this system was designed to complement the others so you can rest easy knowing that the matched components in this kit will work correctly. The incorrect front suspension geometry of the A-Body that was brought up earlier in this thread is corrected with our Geometry Corrected Upper and Lower front A-Arms that increase caster, improving the camber curve, and give you additional camber/caster adjustment. This kit also comes with custom-valved Bilstein shocks that are matched to the spring rates and vehicle. There is a lot more adjustability built into this kit beyond just camber/caster. The new rear sway bar is adjustable so you can tailor the roll-stiffness to match your wheel/tire combo, the layout of the autocross course you are driving, and your own driving style. Our billet upper trailing arms are also adjustable so that you can get the correct pinion angle to improve your launch. For more information on our Total Vehicle System please visit our website: http://www.hotchkis.net/stage-2-tvs-...ll-block-.html

[Captain]

Lets talk tires now

Remember I'm on a shoe string budget. 15" stock car style rims are cheap and easy to come across, but mostly in 8"W versions. 10" are available for slightly more. I'd like to have a set of rims/tires dedicated to autocrossing and I think the brake kit I've put on the car will allow me to downsize wheels to 15" and clear everything. If I can get a set of 10"W wheels to fit on the car- is there any draw backs to running a 17" wheel versus a 15" wheel?

Ideally I'd like a 15"x10" set up- which would probably be something like 275x45x15, right? Handling wise, how much different would it feel on track versus the current 225x45x17?

[SSninja]

I think that the tire options for 15" wheels are pretty limited.

Did a 30 second search for a 275/xx/15, and this was the only result with an aspect ratio less than 50:

http://www.tirerack.com/tires/tires....wtpackage=true

It's also available in a 275/50ZR15, as is the BFGoodrich g-Force T/A Drag Radial

[Captain]

I just threw the camber gauge on for the first time a few minutes ago- it won't thread on 2 turns before I bottom out on the wheel bearing nut. There is little to no vertical slop in the gauge though, it threads on enough that the free spindle on the end starts spinning.

RF: +1 degree
LF: +0.75 degree

Does that split seem right? Or is my gauge not threaded on far enough?