autocross tire pressure?
Thread Starter
Track Day
Joined: Nov 2006
Posts: 21
Likes: 0
autocross tire pressure?
I will be participating in my first autocross next week and need advice from the experts on proper tire pressure setting.
I have an 03-996-C4S with 18 factory wheels, 225/40 front and 295/30 rear, with Bridgestone S02A's.
For street driving I have been using the factory recommended 36 front and 44 rear. For autocrossing how much higher should I increase the pressure? the maximum for my S02A's is 44 front and 50 rear.Thanks in advance for the recommendations.
I have an 03-996-C4S with 18 factory wheels, 225/40 front and 295/30 rear, with Bridgestone S02A's.
For street driving I have been using the factory recommended 36 front and 44 rear. For autocrossing how much higher should I increase the pressure? the maximum for my S02A's is 44 front and 50 rear.Thanks in advance for the recommendations.
Burning Brakes
Joined: Nov 2003
Posts: 966
Likes: 0
From: Mahopac, NY
Originally Posted by jeeper31
Vladimir knows
To answer your question...I think you might want to go the other way. Lower your pressure not raise it. An example...last season with my 944, recommended tire pressure is 29F/36R. I was typically running 29F/32R and had great results.
I would recommend starting from the factory recommendations. See how the car behaves and lower it in 1-2 lbs. increments (front, rear, or both) until you get your desired result.
Instructor
Joined: Jan 2002
Posts: 169
Likes: 0
From: San Francisco
If this is your first autocross ever, then I wouldn't worry too much about tire pressure. Just set them to something reasonable, get a good instructor and have fun. If you get the chance, ride with an instructor or have him or her drive your car. Then you'll see how far off the time you are regardless of the tire pressure setting. Don't worry, we all started off as beginners at one point, but it's a lot of fun.
I have pretty similar tire sizes to you. For street tires, I like about 40 hot all around. Usually I run 38 in the front and 39 in the rear cold to start. Typical AX runs don't warm up my tires enough to change the pressure drastically.
I'd also suggest finding someone else running a similar car and ask them. People are generally pretty friendly at an ax, especially with beginners.
I have pretty similar tire sizes to you. For street tires, I like about 40 hot all around. Usually I run 38 in the front and 39 in the rear cold to start. Typical AX runs don't warm up my tires enough to change the pressure drastically.
I'd also suggest finding someone else running a similar car and ask them. People are generally pretty friendly at an ax, especially with beginners.
Originally Posted by SET
I will be participating in my first autocross next week and need advice from the experts on proper tire pressure setting.
I have an 03-996-C4S with 18 factory wheels, 225/40 front and 295/30 rear, with Bridgestone S02A's.
For street driving I have been using the factory recommended 36 front and 44 rear. For autocrossing how much higher should I increase the pressure? the maximum for my S02A's is 44 front and 50 rear.Thanks in advance for the recommendations.
I have an 03-996-C4S with 18 factory wheels, 225/40 front and 295/30 rear, with Bridgestone S02A's.
For street driving I have been using the factory recommended 36 front and 44 rear. For autocrossing how much higher should I increase the pressure? the maximum for my S02A's is 44 front and 50 rear.Thanks in advance for the recommendations.
Burning Brakes
Joined: Oct 2006
Posts: 1,066
Likes: 1
From: NE Ohio
What I did years ago was start with factory pressure, take shoe polish and stripe a couple of spots on the edge of the contact patch, right to the end of the tread. Run a lap and check how much roll the tire is getting (how much polish you took off) and adjust from there. Idea was to get tires to roll to about the edge of the usable tread, not more, not less. There is no magic pressure. Hope that helps!
Jon
Jon
Last edited by JonH; Mar 16, 2007 at 09:09 AM.
Race Car
Joined: Oct 2003
Posts: 3,907
Likes: 1
From: Long Island, NY
Originally Posted by arbeitm
LOL...were you drunk last night or something.
To answer your question...I think you might want to go the other way. Lower your pressure not raise it. An example...last season with my 944, recommended tire pressure is 29F/36R. I was typically running 29F/32R and had great results.
I would recommend starting from the factory recommendations. See how the car behaves and lower it in 1-2 lbs. increments (front, rear, or both) until you get your desired result.
To answer your question...I think you might want to go the other way. Lower your pressure not raise it. An example...last season with my 944, recommended tire pressure is 29F/36R. I was typically running 29F/32R and had great results.
I would recommend starting from the factory recommendations. See how the car behaves and lower it in 1-2 lbs. increments (front, rear, or both) until you get your desired result.
Thread Starter
Track Day
Joined: Nov 2006
Posts: 21
Likes: 0
Thanks for the advice. My concern is not yet making the fastest lap - maybe my 2nd AX. For now I just want to avoid unnecessarily trashing the tires. I have taken her out a few times in parking lots to find the limit - better then finding out the hard way - which has resulted in more wear then I expected. As recommended I plan to start out at or a little higher then the factory recommended levels and reduce from there until they roll to the tread edge. Now it looks like the more important issue for the AX will be several inches of wet snow.
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Pro
Joined: Nov 2006
Posts: 563
Likes: 0
From: Tibet
Originally Posted by HarryD
Hi,
You will want to add a few psi (say about 5) to get started and then use the shoe polish to figure out if you need to go up or down from there.
Have fun!
You will want to add a few psi (say about 5) to get started and then use the shoe polish to figure out if you need to go up or down from there.
Have fun!
do a couple of laps to get your tires hot, get off the track, take a measurement and put down some shoe polish, and go back out for 1 hard lap.
if you didnt scrub off any polish, take it down a notch, if you are scrubbing off polish, pump it back up.
===
also, for Auto-X purposes, you usualy get 1 lap at a time, which means your tires dont get to their optimum temperatures right away, some tires (like an RA1) get really sticky only after a couple of laps on a full blown track.
for that then you would ahve to compensate at an AX event by pumping more air.
===
having said that, assuming that your suspension is done up well enough, the best way to figure out your tire pressures is to you a pyrometer on the inside outside and middle of the tire the moment you get off the track on all 4 tires, this however requires quick hands and 4 people
Addict
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Joined: Jul 2002
Posts: 374
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From: IL
Originally Posted by BlkC4S
... I have pretty similar tire sizes to you. For street tires, I like about 40 hot all around. Usually I run 38 in the front and 39 in the rear cold to start. Typical AX runs don't warm up my tires enough to change the pressure drastically.
I'd also suggest finding someone else running a similar car and ask them. People are generally pretty friendly at an ax, especially with beginners.
I'd also suggest finding someone else running a similar car and ask them. People are generally pretty friendly at an ax, especially with beginners.
Instructor
Joined: Apr 2005
Posts: 203
Likes: 0
From: Vancouver, Canada
i have found the best way is to go pick up some shoe polish and a cheap infra-red temp laser... you can get them at most decent autoparts stores.
take the car to a big OPEN parking lot.
mark the tires in 4 spots along the edge of the shoulder with the shoe polish.
make sure your pressures are where the factory tells you.
mark off a big circle with cones if you have some... say 50-100ft diameter.
do a couple of laps in one direction and then get out and measure the tire pressures on the inside edge, center and outside edge as well as check to see where the shoe polish has worn off... this is on the outside tires you were just cornering on.
the ideal is to find a balance between even temps across the tire and even wear at the shoulder. you want to use all of the tread on the shoulder WITHOUT rolling over onto the side wall.
if you are on the side wall you need more pressure.
if you are not all the way onto the shoulder you need less pressure. you can also use this to dial in your camber settings if you can adjust for it.
take the car to a big OPEN parking lot.
mark the tires in 4 spots along the edge of the shoulder with the shoe polish.
make sure your pressures are where the factory tells you.
mark off a big circle with cones if you have some... say 50-100ft diameter.
do a couple of laps in one direction and then get out and measure the tire pressures on the inside edge, center and outside edge as well as check to see where the shoe polish has worn off... this is on the outside tires you were just cornering on.
the ideal is to find a balance between even temps across the tire and even wear at the shoulder. you want to use all of the tread on the shoulder WITHOUT rolling over onto the side wall.
if you are on the side wall you need more pressure.
if you are not all the way onto the shoulder you need less pressure. you can also use this to dial in your camber settings if you can adjust for it.
Thread Starter
Track Day
Joined: Nov 2006
Posts: 21
Likes: 0
for the first AX starting off at the factory recommended 36/44 worked well - good grip and did not kill the tires. one thing learned is an important factor is experience (relative to other aspects such as tire pressiure) - my times got better with each run. thanks for all the pressure recomdnetations. i know thes will help and i will be will be using them soon.
