Autocross Tires and Tire pressures

[roger]

I was talking with another Lightning owner at the recent SEMA show, and he asked what I used for tirepressures.

I use BFG R1a's 295x35xZR18's inflated to (hot) 49F/39R (small, tight tracks) down to 47F/37R on long, fast tracks.

I also leave the truck in 2nd (never shift) and it allows the truck to use its ample torque to pull itself out of the hole and reduce wheelspin to a minimum.

[tntcbra]

It is amazing how much required tire pressures can vary, not just from vehicle to vehicle, but from tire to tire. I run on street tires in my Cobra and recently changed from Falkens to Comp T/As. With the Falkens, I ran 42F/38R and the car was balanced quite nice. Sure, it is still a Mustang and the front end didn't always stick, but overall it was good.

The first event on the Comps woke me up. I thought I could get away with the same pressures, only to find them way too low. I rolled the front tires down nearly an inch on the sidewall. And this on a 40 series tire! Anyway, I ran the pressures up, 47F/43R and the car was great. Consider it a lesson learned!

Tim

[trmn8er]

I'm running the stock 275/40-17 Goodyear F1 GS tires on my '03 Cobra Coupe until next year. I also just get into second gear and let her rip. My pressures are about 48-50 in front (to prevent rollover and understeer) and about 30-34 in the rear (low enough to get a good hookup during acceleration out of the corners). Works OK for now, but I know that a set of Kuhmo's will work a lot better!:cbra:

[NeilBerry]

Last year I competed in some Open Road Racing events in Nevada (www.openroadracing.com). The experienced drivers said that they run higher pressures. My tires list the maximum pressure as 32lbs (which is how I ran them), yet the pictures of my tires show a flatness while driving at speed (140 mph).

Any opinions on whether to run pressures that are higher than manufacturer limits.

[roger]

Originally posted by NeilBerry
...Any opinions on whether to run pressures that are higher than manufacturer limits.

Mfgr's listed pressures are a DOT requirement. To find out exactly what pressures you need to run all you need is a bottle of white shoe polish and a pyrometer, and then do some runs. Use the shoe polish to mark the tread and about an 1" down the sidewall. Do the run and then immediately check tire temps. Optimumally the temps should be even all the way across. If the car is dual-duty (also a daily driver), chances are you'll never get the temps completely even across due to alignment settings, but you can tell you've done all you can do after you start getting close (you change pressure and the temps start drifting away again). Use the shoe polish to tell how much rollover you're getting on the sidewall.