Autocross-Tire pressure???

[klever402]

I was just curious to what tire pressure you guys are autocrossing with? I have a 95 Sl2 with 205-50-16 g-force sports?? Everyone is telling me to run about 40 psi to prevent tire roll over. Just seeing if anyone had a good Front-Rear combo that has worked well. Thank you for your time.

[ProDarwin]

What suspension are you using. I just change my pressures to my preference. I usually run around 40psi front to prevent rollover. I start around 40 in the rear also, but drop it if the ass end of the car gets too loose.

[Tom92SCm]

Azenis RT-615 tires-- 41 psi front and 37 psi rear.

-2.5* camber front, -1.5* camber rear. Toe is set at nearly zero all around.

--Tom

[klever402]

I just have a couple simple mods, H&R springs with KYB struts, front tower brace. I have played around with tire pressure a little bit, there is a horseshoe shaped road with little traffic that I have been "testing" on, it was about 60 degrees when I was doing this. I aired them up to 40 all around and did notice the rear was pretty loose, noting that saturns are very light to compared to other cars I find it a little tricky to get to perfect combo, so I went down to 36 in the rear and 39 in front seemed to work pretty good but I figured I would do a post on here to get a little input. Also the last 3 auto cross events it has been rather cold here in Omaha, NE, however this weekends event is calling for 92 degrees, compared to 50 degrees in past three events. So I worry the temp is going to throw me off a little bit and hoping that someone from a warmer part of the country will chime in. Thank you for your time!

[LUNCHBOX]

My setup is almost identical to Tom's ^^^^ except I am running the older Azeni's RT-215's still. I usually start with 40 in the front and 36 in the rear and go from there. The pavement get's damn hot here in Florida during those late summer months.

[S3aturnR]

I was just curious to what tire pressure you guys are autocrossing with? I have a 95 Sl2 with 205-50-16 g-force sports?? Everyone is telling me to run about 40 psi to prevent tire roll over. Just seeing if anyone had a good Front-Rear combo that has worked well. Thank you for your time.

the last event i ran, i had 36psi rear and 34psi front. that was with 205/50-15 kumho ecsta v710 tires. won the class by about 1.2 sec...


s3aturnr

[cloud819]

You still have relitive stock balance in your car. If you want rotation your best bet is a large pressure difference between front and rear. Normally higher in the front and lower in the rear is the way to go.

The idea is to maximize contact patch in the wheels that need to grip, without making them rollover. And minimizing the contact patch on wheels that need to slip without destroying the tire; Via rollover or blowout from over pressure.

With your setup I would try 38 front and 32 rear to start out with. Adjust the rear up or down to taste. Beware of high pressures on the front because it can cause you tires to balloon and reduce the contact patch. You may find that ballooning the rears gives you better results than running lower pressures in the rear, so that it worth trying as well.

What is tough is the you are trying to ballance the car while getting the maximum lateral prerformance out of it as well. It is amazingly easy to make a balanced car that produces nothing when it comes to lateral force using tire pressures. The idea is to maximize flexablity (making you car able to respond well to mid turn corrections) while maximizing cornering power. For a FWD, poorly weight balanced car you are constantly trading off on those to properties. Carefully find a good balance of holding ability and manuverablity.

My car has had a lot of suspension changes to effect its balance in a turn. I'm now running 38F/36R, and changing that a bit for course tastes. I'm able to let the suspension handle more of my balance. Now I just try to get my tires to there maximum holding potential.

[charcoal]

A trick I saw some guys/gals do when I was a member of the Porsche
Club of America and hanging around the SCCA freaks, was to take chalk like that found in scraps of sheetrock/drywall and thickly mark the tire sidewalls in a line straight from the axle to the tread. Then go tearing through the course once.
Afterward check the chalk for wear patterns. If the chalk is worn off way up into the sidewall, add more pressure, if the chalk is not worn deep into the tread, bleed off pressure. This in effect 'tunes' the tire sidewall flexure for optimal tread contact at the limits of tire adhesion.
These chalk marks are then worn like badges of courage in the clubhouse parking lot at the end of race-day.