Auto X May 5th
#2
05-04-2012, 06:08 PM
Since no one else has replied...
Hey guy, I am not an expert on tire pressures, but I did learn a few things while co-driving with 2007 and 2008 SCCA HS Champion, "mrFroge." If you need a starting point, maybe this might help.
When I test ran my Fit with OEM tires, mrFroge suggested that I start at 40 psi. The higher than stock psi was to help make the tires more responsive, keep them from overheating, and to keep the tires from rolling off the rims.
To help determine if the tires were "rolling, he would chalk up the side/edges of the tire. So, after running a lap, he was able to see how far the tires were "rolling" over the edges. If he saw scuff marks climbing too high onto the sidewall, he would add more air. He would also use a temperature gun to check the inside and outside tread temps to determine if we were getting maximum tread contact, for that course.
Too little or too much psi will affect grip. Altering front / rear pressures could turn a beautifully rotating Fit into an under-steering "Pig." On occasions, mrFroge would experiment with psi between runs while "I" was at the wheel. As a result, corner marshals would often flee their posts as I plowed through their cones!
To answer your question, if you are running the Bridgestone OEM tires rated at 44 psi max, then I would try starting with at least 35 psi.
44 psi X .80 = 35.2 psi
If your Fit shipped with the Dunlops rated at 51 psi max, then I'd might suggest starting at 41 psi.
51 psi X .80 = 40.8 psi
Note, I'd run a few more psi up front. Doing so seems to help rotation, or you can try putting more psi in the rear, if you want to scare the turn Marshals.
If anyone else can chime in, please do. I would hate to have steered mkane in the wrong direction.
FYI, be aware that you will scrub off a lot of tire life. My calculations show that I lost about 5,000 miles per lap. I normally get about 50-60K on a set of tires. I didn't even get 20K miles on the set of Yokohama S. Drives that I AutoX'ed for only 8 laps!
Anyway, have fun! It does get addicting...i.e. until it comes time to buy tires again, and again. I was not so much worried about buying tires...it was trying to explain why I had to buy them so often. Mrs Mac kinda curbed my dreams of being an up and coming SCCA Champion!
When I test ran my Fit with OEM tires, mrFroge suggested that I start at 40 psi. The higher than stock psi was to help make the tires more responsive, keep them from overheating, and to keep the tires from rolling off the rims.
To help determine if the tires were "rolling, he would chalk up the side/edges of the tire. So, after running a lap, he was able to see how far the tires were "rolling" over the edges. If he saw scuff marks climbing too high onto the sidewall, he would add more air. He would also use a temperature gun to check the inside and outside tread temps to determine if we were getting maximum tread contact, for that course.
Too little or too much psi will affect grip. Altering front / rear pressures could turn a beautifully rotating Fit into an under-steering "Pig." On occasions, mrFroge would experiment with psi between runs while "I" was at the wheel. As a result, corner marshals would often flee their posts as I plowed through their cones!
To answer your question, if you are running the Bridgestone OEM tires rated at 44 psi max, then I would try starting with at least 35 psi.
44 psi X .80 = 35.2 psi
If your Fit shipped with the Dunlops rated at 51 psi max, then I'd might suggest starting at 41 psi.
51 psi X .80 = 40.8 psi
Note, I'd run a few more psi up front. Doing so seems to help rotation, or you can try putting more psi in the rear, if you want to scare the turn Marshals.
If anyone else can chime in, please do. I would hate to have steered mkane in the wrong direction.
FYI, be aware that you will scrub off a lot of tire life. My calculations show that I lost about 5,000 miles per lap. I normally get about 50-60K on a set of tires. I didn't even get 20K miles on the set of Yokohama S. Drives that I AutoX'ed for only 8 laps!
Anyway, have fun! It does get addicting...i.e. until it comes time to buy tires again, and again. I was not so much worried about buying tires...it was trying to explain why I had to buy them so often. Mrs Mac kinda curbed my dreams of being an up and coming SCCA Champion!
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