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      11-05-2011, 04:11 PM   #1
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autocross tire pressures?

I'm running 265mm RE-11s all around, with -2.5 camber all around, and zero toe. What kind of cold tire pressures should I start with?

I did a quick search but didn't find anything
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      11-05-2011, 05:20 PM   #2
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Easiest way, I found, is to just mark your sidewall with white shoe polish, fill it to 38 PSI and adjust accordingly. With Hankook V12s (245x275s) I run 36 cold and keep it around 38 hot.
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      11-05-2011, 07:02 PM   #3
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thx
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      11-05-2011, 07:24 PM   #4
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So you're going to autox that little blown beast of yours eh? Should be fun! Let us know how it goes!
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      11-06-2011, 03:23 PM   #5
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I'll post some videos in my build thread. Street cars ran from about 45seconds to 68 seconds, I think my best time was 52.9 + 1 cone. Most fast cars were under 52 seconds. I have a lot of learning to do. As per the instructor, I ran with TC on since the surface was funky for 3 runs, and on my last run I turned it off and got sideways hard, and ate a bunch of cons while sliding to the finish line. It was really fun!

I need to improve my smoothness, and pretty much everything else. hahahha
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      11-06-2011, 06:05 PM   #6
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I run RE11s, 235 in front 265 in back. I start them at 35 all around and go from there. Never seen anyone use shoe polish though...chalk is the standard I see
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      11-07-2011, 09:21 AM   #7
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Up hear in Seattle, it tends to get wet. Chalk wouldn't last putting it on, but that's a good point, chalk will work in the dry.
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      11-07-2011, 09:58 AM   #8
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I ran 33psi all around cold, and didn't have significant roll-over of the tires
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      11-07-2011, 10:46 AM   #9
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Quote:
Originally Posted by Roffle Waffle View Post
I ran 33psi all around cold, and didn't have significant roll-over of the tires
<my opinions in the context of autocross>

Your tires were fine in terms of roll-over. Being only about 50 degrees out you need to lower your rears to factory setting (which I would do anyway) so you get any heat in the tires which are mostly lost between runs. Not having a baseline, it becomes difficult to determine the effects of increasing/decreasing pressures. We have test-and-tune sessions for these kind of exploratories.

Rather than using shoe polish or chalk markings, you can use a paint pencil (I keep running over mine and having to buy new ones) and make small discrete lines on the shoulders of the tires. They're handy for recording tire history as well. I mark the tire positions when swapping to/from snows, etc.

Probably an even better idea is just to carefully use the tire polish stuff up to your acceptable roll-over point and see if they get scrubbed. You'll have pretty sidewalls and roll indication at the same time! :-)

</my opinions in the context of autocross>
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      11-07-2011, 10:56 AM   #10
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Yeah, I was really expecting more grip out of my rears on that last run, a few psi would have likely made a significant difference. I'll also pick up a paint pencil. I definitely want to run as many autocrosses as I can next season. I had visions of flying around the course as I was falling asleep. hahaha

I also think I could have carried more speed through the slaloms, and positioned the car better on the returning sections
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      11-07-2011, 02:24 PM   #11
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That is what will happen after a couple autocrosses. It's always...well I could of attacked this better..haha.

Tire pressures are always finky. They are never the same across the tire spectrum. It always depends if you're running on a different surface (for example I had to increase my PSI by about 3 all around when I ran on tarmac).

At the end of the season I was set around 36 front and 34 rear IIRC with Toyo T1Rs. Now with Hankook RS3s I get to experiment all over again.

If you can ride with others that have been auto-xing for awhile...it will always help.
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      11-07-2011, 02:46 PM   #12
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definitely. I rode with kklin, in his stock m-coupe on stock contis

I was surprised he didn't spin it with TC off AND sport on. Thats tough to modulate on a tight course
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      11-07-2011, 03:35 PM   #13
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Quote:
Originally Posted by Roffle Waffle View Post
definitely. I rode with kklin, in his stock m-coupe on stock contis

I was surprised he didn't spin it with TC off AND sport on. Thats tough to modulate on a tight course
First 3 autocrosses I did with TC off (the first 3 times I drove this car auto-xing) I spun it at least 5-6 times.

I of course was transferring from an E46 325xi, so it's alittle different as well

I don't like SPORT on, the gas pedal is too sensitive.
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      11-07-2011, 09:00 PM   #14
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Agreed, I can't imagine running with Sport mode on.

Congrats on transitioning to the phase where you are starting to realize what you can improve on! Now the work really starts!!! I see a set of tire blankets in your future...
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      12-18-2011, 02:13 PM   #15
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Tire pressure advice is one of the most all over the maps areas on forums I've read. Tire pressures are dependent on setup, tire, conditions, your driving style and surface. I've run on virtually every UHP tire out there in the past two years. For RE-11's, they get warm fast and suffer from overheating if it is hot/dry. On a typical 7--80 degree dry day, I would run 33 front/31 rear and bleed down as pressures gained from runs, about the same as RS3's, Yokohama AD08 and Dunlop SS. Adjust -2# for wet or cold days. For Toyo R1R, I've run 29# all around in warm, and as low as 27# in the wet or cold.
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      12-21-2011, 10:27 AM   #16
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Quote:
Originally Posted by Roffle Waffle View Post
I ran 33psi all around cold, and didn't have significant roll-over of the tires
If you're running 33 psi cold and didn't see enough roll-over of the tires, you're probably not using up all of your available grip.
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      12-21-2011, 12:15 PM   #17
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depends what you define as "enough roll-over". I'm not running stock tires/sizes/wheels. Every run was with an instructor, and he didn't mention anything about me not pushing hard enough and he was the one who inspected my tires before and after. But you could be right
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      12-21-2011, 12:30 PM   #18
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I gauge the inflation by the arrow markings on the tire wall indicating optimal tread use after the first couple of runs.
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      12-21-2011, 01:00 PM   #19
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Quote:
Originally Posted by Roffle Waffle View Post
depends what you define as "enough roll-over". I'm not running stock tires/sizes/wheels. Every run was with an instructor, and he didn't mention anything about me not pushing hard enough and he was the one who inspected my tires before and after. But you could be right
Stock tire/sizes are irrelevant. Outside of R-Comps most street tires will operate the best at around 38-42 PSI hot. Since autocross runs are never long enough to significantly heat up the tires, you need to shoot for at least 36 psi cold, especially in colder climates (I'd go as high as 38 psi cold if the temperature is below 60ºF, since it's unlikely you'll be able to put enough heat into the tires to increase the inflation pressure by 2 PSI).

Using the PSI and roll-over as a gauge will also improve your driving, because if you're significantly lower than the ideal pressure and you're not seeing any roll over, you can safely bet you've not used up all your available grip yet. If you're at the ideal pressure and you're still seeing significant roll over, you're overdriving the car and you're actually slower by unnecessarily sliding the car around.

Which isn't to say you need to push harder. It is but an indication that you've probably left some speed in the turns and the tires will likely continue to grip even if you enter some of the turns at higher speed. Usually what I do for our AX, is I start the day at 30 PSI only because we do our recon laps in the morning and they're back to back to back laps without any significant cool-down time (so tires will heat up like track sessions), but for the timed runs I pump the tires back up to 37 PSI and monitor the amount of roll-over/wear to see if I'm leaving traction on the table or over-driving the car, since the tires do cool down between runs.

Of course, this is assuming that your car is aligned with some camber in the front. If you're on stock camber then the rule is altered a little, since your ultimate grip is less with less camber.
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      12-21-2011, 02:09 PM   #20
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Unfortunately there's little info out there about recommended z4m specs so I was left guessing. I will try higher psi next time. I had bad straight line grip, so I didn't want to inflate the rears too much, and lose even more traction. But then again there are few straight line sections in autocross. Anyway, I ran -2.5* camber all around. Now I'm down to -1.5* in the rear for better off the line traction
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      12-21-2011, 02:14 PM   #21
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i like 38-40psi hot...... car feels really good as close to this as possible.
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      12-21-2011, 07:26 PM   #22
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Quote:
Originally Posted by The HACK View Post
Stock tire/sizes are irrelevant. Outside of R-Comps most street tires will operate the best at around 38-42 PSI hot. Since autocross runs are never long enough to significantly heat up the tires, you need to shoot for at least 36 psi cold, especially in colder climates (I'd go as high as 38 psi cold if the temperature is below 60ºF, since it's unlikely you'll be able to put enough heat into the tires to increase the inflation pressure by 2 PSI).

Using the PSI and roll-over as a gauge will also improve your driving, because if you're significantly lower than the ideal pressure and you're not seeing any roll over, you can safely bet you've not used up all your available grip yet. If you're at the ideal pressure and you're still seeing significant roll over, you're overdriving the car and you're actually slower by unnecessarily sliding the car around.

Which isn't to say you need to push harder. It is but an indication that you've probably left some speed in the turns and the tires will likely continue to grip even if you enter some of the turns at higher speed. Usually what I do for our AX, is I start the day at 30 PSI only because we do our recon laps in the morning and they're back to back to back laps without any significant cool-down time (so tires will heat up like track sessions), but for the timed runs I pump the tires back up to 37 PSI and monitor the amount of roll-over/wear to see if I'm leaving traction on the table or over-driving the car, since the tires do cool down between runs.

Of course, this is assuming that your car is aligned with some camber in the front. If you're on stock camber then the rule is altered a little, since your ultimate grip is less with less camber.
And to monitor roll-over, best to do is mark up your tires!



I use Chalk...cheap and not messy. I have yellow, blue, pink and green...
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