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[MarkR171]

I bumped up my tire pressure in the front tires to 43psi today for autocross as I was still rolling over the tires a bit. The car actually feels a LOT better now with that amount of psi. Steering response is improved and it seems to be more neutral through long corners.

Just wondering if there are any negative effects that might occur running ~7 psi over the door jamb recommended pressures on a daily basis.

Tires: Dunlop Star Specs 225F/255R on stock wheels and stock suspension.

Thanks, chalk up another DS win for the 135i team , faster than all the STU folks too, and that's not including the full second I slashed in fun runs with a passenger after changing my pressures!

[IGoFast1589]

Higher tire pressures will give you better responsiveness, a stiffer feel and less overall grip while lower tire pressures will give you less responsiveness, a softer overall feel and more grip. There is no problem with running the tire pressures at that level other than the possibility of a negligable increase in tire wear. That's why you see guys that drag race their cars with very little air pressure in their tires. If it helps the feel of the car then go for it!

[MarkR171]

Thanks guys, I'll probably keep it in the high 30s for daily use and just bump it up for autocross then.

[IGoFast1589]

Originally Posted by MarkR171

Thanks guys, I'll probably keep it in the high 30s for daily use and just bump it up for autocross then.

Sounds like a plan.

I run high pressures on my STi because the AWD gives plenty of grip and the feel and stiffness become the more important factors. My friend does the same with his turbo R32, but it really boils down to what you are looking for and the specific situation. Try changing the pressures dramatically in relation to eachother to really feel the difference for yourself and see what you like best.

[VMRWheels]

That is interesting seeing such a high PSI being used to performance driving. I have used Z1 SS before and have found a happy medium between 30-35 or so for track use.

-Charles@VMRWheels

[MarkR171]

I know of a guy in an STU class '04 Subaru STi running 48psi front and 45 psi in the back for his star specs...

On the track, your tires probably heat up more than on an autoX course so the pressures raise a bit while driving. Also, not as many low speed tight cornering on a track like the first gear 90* or greater autocross corners.

[cpt97m3]

Originally Posted by VMRWheels

That is interesting seeing such a high PSI being used to performance driving. I have used Z1 SS before and have found a happy medium between 30-35 or so for track use.

-Charles@VMRWheels

AutoX use often requires higher pressures than track events, especially on the front tires.

[Eddy@ApexWheels]

nothing about that sounds unusually, especially considering that you are running tires designed for use on wider wheels.

[IGoFast1589]

Originally Posted by MarkR171

I know of a guy in an STU class '04 Subaru STi running 48psi front and 45 psi in the back for his star specs...

On the track, your tires probably heat up more than on an autoX course so the pressures raise a bit while driving. Also, not as many low speed tight cornering on a track like the first gear 90* or greater autocross corners.

Yup, exactly!

Think about a 3,xxx pound vehicles weight being thrown onto a helpless little tire through an 85 mph turn and being held at a constant radius for a longer duration vs the same vehicle weight being thrown onto the same tire at 10 mph for a short duration of time. Which do you think is being subjected to more? Hmmm....!

[BrokenVert]

Originally Posted by IGoFast1589

Yup, exactly!

Think about a 3,xxx pound vehicles weight being thrown onto a helpless little tire through an 85 mph turn and being held at a constant radius for a longer duration vs the same vehicle weight being thrown onto the same tire at 10 mph for a short duration of time. Which do you think is being subjected to more? Hmmm....!

That equation has to do with both the speed and the radius ofthe corner so it depends!

V/r^2 = a than plug into F=m*a which is the centripetal force on the whole car. Then by an understanding of vehicle dynamics you can calculate the load on one tire

And Mark that's about what I run at autox too. I'm also still waiting on that plate frame

[IGoFast1589]

Originally Posted by BrokenVert

That equation has to do with both the speed and the radius ofthe corner so it depends!

Yeah, I am just trying to paint a more vivid picture. There certainly is a LONG list of variables that come into play, without a doubt!

[MarkR171]

Originally Posted by BrokenVert

I'm also still waiting on that plate frame

LOL You're killing me man. I meant to grab one for myself to use on my front plate but I even forgot about that at the end of the day.

Thanks for the input guys, glad to know I'm not the only one raising pressures to that level, and makes me think about trying a bit more next time since 43/44 felt so good on my last run. (Good enough to stop the plowing and cut .6 off my time in 1 run after the change... with a passenger)