Autocross Tire Pressure and Chassis Set Up

Mooch · #1 (**permalink**) 06-28-2010, 06:51 PM

I'm taking my ERA 427 (six weeks old) for its first autocross in the next few weeks, and I was looking to get some advice on some initial tire pressures and chassis set up.

For reference, I'm at 2700# with me in the car, with the ERA IRS and four corner Spax coilovers at 6 clicks out. 15" pin drive wheels with MT E/T Street radials with 28psi in front at 26psi in the rear for street driving. I have front and rear sway bars - don't know the settings off the top of my head on those.

Since I'm a novice at autocross, I'll probably be focusing on the driving more than the setup, but I might as well start out at a reasonably good setup.

I probably won't change any chassis settings the first day out, and will work on getting the proper tire pressures. Next time, work on coilovers. Next time, sway bars, etc.

Thinking of starting at 38/36psi for the pressures.

Any advice?

LMH · #2 (**permalink**) 06-28-2010, 10:56 PM

I read this article and lots of good info: http://www.tirerack.com/features/solo2/handbook.htm
Larry

COBRANIP · #3 (**permalink**) 06-28-2010, 11:44 PM

To get tire pressures in the ball park, rub some chalk on your sidewalls near the transition from the tread. After a run you will be able to tell how far over the tires are rolling. If they are rolling too far over (rub chalk away too high on the sidewall) then you need to increase tire pressure.
Good luck and HAVE FUN.

P.S. Most good autocrossers will be more than happy to give you advice and tips....so at the course, don't be shy.

WardL · #4 (**permalink**) 07-08-2010, 09:06 PM

I too am considering autocross. I just found out the town I live in has a club and they run 6 races a year. How do Cobra's handle on these types of low speed courses? It seems a little funny to have 500 HP and go on a relatively low speed course. I'll probably be shocked to see how fast cars are flying around the cones! I would love to hear how others have done. For sure the driver and particular Cobra will make a huge difference. Good luck and let me know how it goes for you.

Oh, the SPF manual says 25 psi for track racing. That is a lot lower than what the link above says. I've heard the chalk suggestion before.

dcdoug · #5 (**permalink**) 08-02-2010, 04:17 AM

I am doing my first autocross this weekend and run GY billboards at 28 psi front, 26 psi rear on the street. I know most people recommend running less psi at a track. Is the same true for autocross?

Excaliber · #6 (**permalink**) 08-02-2010, 06:30 AM

It may be surprising buy many auto cross guys recommend runnng HIGHER psi for the track than on the street. It may be due to the extreme sidewall pressures the tires have to endure in the hard cornering.

In a typical auto cross you will be using 2nd gear only, no shifting, speeds around 60-65 mph max, or less. No way you will use or need 500 horse, but no one else will either.

I ran with a couple of FFR's, street cars BUT, extremely well setup specifically for auto cross. For race day they were prepped and then trailered to the track, not driven. One car was dry sumped, both had IRS, experienced drivers, racing seats, etc. etc.

They were among the top competitors, almost as fast a some VERY exotic full blown race cars. Like the Lotus 7 replica with a small block V8 and massive slicks. The FFR's were real close to HIS time and he was the fastest of the day.

I was considerably slower, even with full race only Goodyear slicks. The dual carbs are a serious problem for me though, side pivot floats don't do well in hard cornering. You go rich on one corner and lean on the next.

Because your only using one gear (like 2nd) I use my left foot for brakeing. Our auto cross here is NOT typical, it's actually a real track and is faster than a cone setup type track. 75 to 80 mph in some parts, really winds the motor up high, but no time to shift, but some guys do anyway.

Fullchat289 · #7 (**permalink**) 08-02-2010, 06:41 AM

Mooch:

I will be doing this same this coming weekend if the weather is dry. I plan to do the same as far as playing with tirepressure first out of the gate. I may run a little stiffer damper settings in the front to see if I can get the front to plant a little better and try my hand at trail braking to neutralize when needed.

Maybe we should keep this thread bookmarked and report back with our settings and results??? In any case, I'll be running BFG for this first time out starting at 30f/30r for pressures and standard 5 clicks on the spax for the AM runs....the corner workers should have fun picking up all my cones...LOL!

- Allen.

dcdoug · #8 (**permalink**) 08-02-2010, 07:57 AM

Is it important to add an extra .5 to 1 quart of oil for autocross like some recommend for a full size track (I have a RR pan)? This will be cone style parking lot autocross, not higher speed airport style autocross.

Any other comments on whether higher/lower tire pressure with billboards is the right approach?

Fullchat289 · #9 (**permalink**) 08-02-2010, 11:32 AM

Quote:

Originally Posted by dcdoug

Is it important to add an extra .5 to 1 quart of oil for autocross like some recommend for a full size track (I have a RR pan)? This will be cone style parking lot autocross, not higher speed airport style autocross.

Any other comments on whether higher/lower tire pressure with billboards is the right approach?

Doug:

My thoughts are that you won't want to add any more oil than what's indicated as "full" on your dipstick.. I've been autocrossing for a number of years now and haven't ever heard of anybody adding more oil. ....but on the other hand, you have reminded me to top mine off. LOL..

As for tire pressure, I would increase from your regular street pressures by a couple of pounds cold, and use the sidewall chalk method described above in another post to see how much the tires are rolling over the sidewall, then adjust from there. The key is you want as much of the tire's tread surface to be in contact with the pavement as possible to maximize your adhesion..

- Allen.

Excaliber · #10 (**permalink**) 08-02-2010, 11:57 AM

I also like to run above the full mark on the dip stick when I'm racing. I've noticed that running above full results in no loss of oil pressure in the hard corners and running at the full mark does cause a small drop in a long corner.

The key is if the engine can handle another 1/2 or full quart. I have a BIG pan (road race, with baffles and gates) so a full quart is not that much more for my volume. IF the extra oil causes problems like smoking or PC valve sucking oil, then it's to much volume.

DAVID GAGNARD · #11 (**permalink**) 08-02-2010, 02:42 PM

Quote:

Originally Posted by Mooch

I'm taking my ERA 427 (six weeks old) for its first autocross in the next few weeks, and I was looking to get some advice on some initial tire pressures and chassis set up.

For reference, I'm at 2700# with me in the car, with the ERA IRS and four corner Spax coilovers at 6 clicks out. 15" pin drive wheels with MT E/T Street radials with 28psi in front at 26psi in the rear for street driving. I have front and rear sway bars - don't know the settings off the top of my head on those.

Since I'm a novice at autocross, I'll probably be focusing on the driving more than the setup, but I might as well start out at a reasonably good setup.

I probably won't change any chassis settings the first day out, and will work on getting the proper tire pressures. Next time, work on coilovers. Next time, sway bars, etc.

Thinking of starting at 38/36psi for the pressures.

Any advice?

First time out, find someone that has done this a lot and before things get going, walk the course with him and asked questions and listen to the answers, folks will be more than happy to help you out.....my first AC, I think they used a sun dial to time me and I "only" got lost twice while on the course, you'll need to worry about the course more than your set-up for your first few times out.......

One of the fastest cars out there one time was a 16 year old, tall/skinny geeky looking kid in his mom's Honda Civic WAGON, I kid you not, this kid could drive!!!!!!!!!!!!!! made me look like the slow poke I was.......

David

dcdoug · #12 (**permalink**) 08-02-2010, 02:57 PM

I will have a number for friends from our local cobra club there, so I should get plenty of advice. I think I will just leave the tires at the street pressure and not worry about it. I can inflate them further when I'm there if it's a big deal, but I doubt it will be.

I'll be too busy picking up cones.....