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Drive True
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I just noticed the selgp.com link for this forum and checked it out...if you go to the November 2, 2003 MWCSCC Championship Auto-X #8 story (right there at the top) and then scroll down to the bottom where it says WDCR/SCCA Autox-X # 6, Sept 14, 2003, the SGP development vehicle as high as 37 psi front, and 39 psi rear! :eek:

"SGP development vehicle, 2004 Subaru WRX STi, in stock form competed with new tire pressures on the Bridgestone Potenza 090s and took 8th place with a best time of 55.377 seconds in front of Ken Kammerer's 2003 BMW M3. With tire pressures set to 37 psi in the front and 39 psi in the rear and DCCD set fully back open position, the STi exhibited more oversteer than intended; however, the stup was quite confidence inspiring. Further adjustments to tire pressures will be tested in the next auto-x as it wa clear that the front tires' wear marks were not close enough to the side roll markers; target: 36.5 f and 38 rear pressures."

I thought that you shouldn't inflate tires to more than 35 psi?? Has anyone tried this?
 

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The max. pressures on the 070s are 51 psi. Factory recommended pressures are 36 front and 32 rear, so you can go over 35; and should for track and auto-x events.

Actually we are just writing an interim report on STi that, I hope, will contain good information. The summary for tire pressures: as the tires get worn (or broken-in) we found that we have to increase them a little further to maintain similar balance we experienced at the beginning. During our last two events we used 36.5 front and 38 in the rear. Towards the middle of the session, the car started to exhibit more understeer and fronts started rolling on to their sides. The last event we went up to 39 front and 39 rear, and we had near perfect balance with nearly non-existant understeer. One thing is for sure, the 070s are very pressure sensitive.

Also, I'd like to add that, these tires are lasting us more than we thought they would. We have a tad over 3K mi. on them with the last 2K mi. purely on auto-x and track usage; and we still have over 50% tread left on them. However, we also noticed that the wear rate is increasing now.
 

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Drive True
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Wow...straight from the source...thanks FT!
 

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Yes, thanks for the info.

I was a total NOOB when I took my auto-x instructions last weekend. My tires were at 36F 32R. Way under pressured. The instructor suggested that I start with a 3 PSI bump on each set...they were that low.
 

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SnowbordrWRX said:
Wow...straight from the source...thanks FT!
mx_9 said:
Yes, thanks for the info.

I was a total NOOB when I took my auto-x instructions last weekend. My tires were at 36F 32R. Way under pressured. The instructor suggested that I start with a 3 PSI bump on each set...they were that low.
It is certainly my pleasure.
RadarOnPaws said:
According to the sticker on the door, it's 36/30, however, I noticed when I checked them today that they were at 36/32 (first time I checked since I got my car on the 3rd).
You are correct, my bad; I was writing off memory :) Thanks for correcting me.
 

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FT, did you try lower pressures at the rear, and go up from there? i ran 40f/30r cold on a really tight 2nd gear short course, and it seemed good. i'm gonna have to go up on the rears and see what happens, it sounds like you have a good setup.
 

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norcal-sti said:
FT, did you try lower pressures at the rear, and go up from there? i ran 40f/30r cold on a really tight 2nd gear short course, and it seemed good. i'm gonna have to go up on the rears and see what happens, it sounds like you have a good setup.
We first started with the stock pressures to see what happens, then we came up with the pressures we have now. This always a moving target no question.

Our process is actually quite simple: The most important part is to find the right front pressures. The best pressure is when you hit the side roll markers without going over them, that is when you get the most grip. Since the STi has 60% of the weight at the front, front grip is essential. Once we find this pressure, which varries between auto-x and track (we use about 0.5 to 1 psi less at the track), we set the rear pressures according to how we want the car to handle on the course. The best part with the 070s is that they are sensitive to tire pressures, hence adjusting handling characteristics is easier, almost better than adjustable anti-rollbars :)

With the front pressures set to most grip, if you want the car to have more oversteer, you really want the rears to grip less without rolling to the sides. Hence we increased rear pressures to higher relative to the fronts. The other good part here, the STi has the same tires and sizes all around, so this is easy to figure out. If you have too much oversteer, then decrease the pressure by 0.5 increments; or if not enough, increase with the same increments. So finally, at the current mileage we settled to 39f/39r at this time with stock alignment. The reason the front and rear pressures are the same at this time is that even at optimum pressures, the front tires are worn, so they do grip less than 2K mi. before :) We will rotate tires soon and we will see how things go from there with the above procedure.

As with any chassis adjustment, what counts is the driver's point of view. So, I cannot disagree with you about setting them to 40/30 pressures. However, I suspect, you got similarly pleasent handling from the STi as we did because you had less grip at the rear due to too low pressure. However, I suspect your rear tires did roll over to their sides. Which is also an effective way, but increases uneven tire wear. Did the rears roll over passed the side markers? Also, how many miles do you have on the tires?

I hope I did not confuse things more.
 

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I know this is an old topic however I need some clarification. I was reading on NASIOC forum about tire pressures and found that the reccommendation seems to be to keep the front tires 6psi higher than the rears. The overall feeling was that would counteract our understeer. I am going to try and find the thread I was reading and post it here. I am currently running 34 rear and 40 front based on the recommendations from NASIOC. Would I be better served running 39 front 39 rear. I am looking for a good all around pressure for my spirited daily driving. Thanks for any reply.
 

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for daily driving, i'm running 40-41fr/35-36rr(cold). i will probably bump the rears up a bit more for auto-x, depending on how grippy (or not) the course is.
 

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With our testing we conducted 4th quarter of 2003, which we could not fully complete the tire tests since the tires are pretty much gone (they won't see any more competition), we concluded that the optimum pressures that we would have used in the autoxes would have been 39-40f and 36.5-37.5 r (cold), even go as high as 38 actually.

My comment about 6 psi difference is that it is meaningless. Tire pressure are directly dependent on ambient temps, tire wear at the moment, driving style, etc. One thing you learn in the chassis tuning business is that there are litterally no rules, too many variables to draw linear conclusions.

That being said, start with NASIOC pressures, and adjust between your autox runs depending the environment. Just keep an open mind that when you say to yourself "the car feels pretty good with these pressures" think that it can actually get better ;)

I am willing to bet, you will be closer to the pressures I mentioned up there. That is not because I am smarter or anything like that :) but we did over 3 months of testing on the stock STi, so I am confident of our data ;)

Best of luck. The season is starting, wooohoooo !!!! :D
 

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After reading this post I started messing with pressures. I started at 42psi all around just to try it. Front end felt like it skipped a bit pushing through a tight right hand turn in second(almost like front right tire slipped a little accelerating out of the turn). I now have the pressure set at 39 all around and will give it a go in the morning. It seems like it should be great. --Sin52
 

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Oh yeah, at 42psi when I pulled into the garage there was no dirt on the outer one inch and inner 3/4 inch of the tire (about).--Sin52
 

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Went out for a sunday morning drive. really feels better through the same turns from yesterday. Took it down a couple of dirt roads I know real well. Slides a little more now than with the pressure I had before reading this thread(f32r30), but that would be expected. Man I really need to pad up my seat and buy a bracket and harness. --Sin52
 

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FT.. thanks for your contributions in this thread. I'm attending an AutoX novice school on 2/28 so I found your info to be very useful. I'll be starting out at 39/39 psi.

Thanks, Chris
 

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mx_9 said:
FT.. thanks for your contributions in this thread. I'm attending an AutoX novice school on 2/28 so I found your info to be very useful. I'll be starting out at 39/39 psi.

Thanks, Chris
mx_9, it is truly my pleasure and I thank you for looking at our site. Best of luck with the school, I am positive you will have a blast.
 

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IN CAL here and i am running 35 front and 32 rear on stock rubber ...seems nice not too bouncy may go higher in the spring which is here soon I do plan to get new volk ce28n with (17x7.5) with continental sport contact extreme all weathers on as well
will keep the page posted on those
sman
 

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i'm no master of auto-x but i do overwhelmingly agree that tire pressure is very dependant on the outside temperture. there is a reason drag racers sometimes use tire covers, it keeps the hot sun off the tires and prevents pressure differances from left to right. so while on a hot day one set-up might be great ,it might not be ideal on a cooler cloudy day.
 
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