[stewhatch]

I'm entering my first autocross this weekend and was wondering what I should be running my F & R tire pressures at. Stock 968 Coupe with LSD and 16" wheels. Tires are Dunlop SP 8000 (205-55-ZR16 and 225-50-ZR16). Is the proper setting critical? TIA

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[Georges]

I set mine at 36 cold. During the day I make sure they don't exceed 40 hot. This has been working for me for a number of years at autxo. I don't stress out about this a lot. When I think I've gotten close to 100% of the car I'll check the pressures between runs more often. I usually go home with first place trophy. :-). My goal is to use my humble stock 968 to beat the cars that come off trailers etc. Getting there.. maybe next event <img src="/forum/images/smilies/968/wink.gif" class="smilie" alt="" />

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[PorscheDude]

You can also put some white shoe polish on the edges of your tires to give you indication of how much tread contact is being used.

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[968crazy]

36 all around is a good starting point if the tires are rolling add some pressure. if you ever decide to get serious get stock 17's and put 275/40/17 on front and 295/35/17 hoosier A6's on it then your car will dominate its class assuming you can drive well. 275 up front takes about a 1mm spacer and 2.3 degrees negative camber to fit but the car turns awsome and the braking is outstanding. Good luck and go have some fun!

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[stewhatch]

Thanks a million guys. White shoe polish: I assume if it appears rubbed off you add pressure, correct? There was a supercharged Honda Civic that killed everyone, including a Formula Vee. This autocross thing looks like a LOT of fun.

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[flash]

i've betting you'll be dumping those sp8000s in a very short time - worst tire i ever drove on - no grip - wore like nails though



after carefully inspecting the tires for signs of age and wear, drop the pressure on those tires - they have a very stiff sidewall and a hard compound - i'd start at about 33 and go down from there - you may end up as low as 28 - use the chalk or shoe polish method for sure too

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[PorscheG96]

[quote name='flash' post='53326' date='May 26 2008, 06:56 AM']i've betting you'll be dumping those sp8000s in a very short time - worst tire i ever drove on - no grip - wore like nails though



after carefully inspecting the tires for signs of age and wear, drop the pressure on those tires - they have a very stiff sidewall and a hard compound - i'd start at about 33 and go down from there - you may end up as low as 28 - use the chalk or shoe polish method for sure too[/quote]

No way flash, those tire pressures are way too low for these tires. I had a set of SP8000 on my last 968 and the side wall is actually very soft! I know this based on the feel of the car in corners compared w/ other tires plus I actually mounted those tires on the rims myself and recall the sidewall feeling kinda thin on all 4 tires.



I agree with the other recommendations of 36-40psi hot pressure. You don't necessarily need shoe polish if you just look carefully at the tire side walls after each autocross run. Lately I've been testing 36f/38r using Yokohama street tires just to get a bit more oversteer in the tighter sections, but the range suggested will provide good starting pressures. When I reduced to 35 psi then the sidewall just started to get knicked up, so I haven't run pressures below that...28-33 psi sounds like it would cause damage to the side walls of street tires.

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[flash]

this one is all about how fast and hard you drive - suspension setup plays in here too - a stiffer suspension changes how much weight is shifted to the outside tire - even setup geometry can make a pound or two change - there are too many things to give a "do this" pressure



you absolutely must use some form of testing (chalk, shoe polish, tire temps, wear pattern if you're observant enough, etc) to see what you are doing - where you set them is based entirely on how you are using them - if you aren't tearing up the edges of the pattern, you have too much air in them - if you are rolling them over past the tread, then you need more - it may feel weird at first, and even a bit soft, but the times, and the lessening of breakaway, will tell you that it's right



i had the 8000s too - absolutely hated them - i tossed a perfectly good set a few months after i got the car - second stiffest tire i have had yet - i played with those for a while, trying to find something that worked, and gave up - even on the street i was setting the 8000s to 34 front and 33 rear - any more than that and they were slipping all over the place - got a lot miles out of them though



stiffest has been the bridgestone S0-3 - i set the S0-3 at 31 cold rear and 30 cold front for track use, and those are 30 and 35 series - i use both a tire temp gauge and the chalk method to determine what pressure to set, and how to get the outside of the corner to wear - the faster i go, the lower the cold pressure - on the street i run 37 front and 36 rear, but that is just because of potholes and the low profile - any less and i bang rims - at that pressure though, i am not using all of the tire, and they heat up WAY too much on the track - now that i finally got the springs changed back out, and the shock and strut settings pretty much sorted out, i might be able to drop another pound



lol - on the lighter cars, we were starting off at 25 cold on a 205-50-15 Y2000

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[stewhatch]

[quote name='flash' post='53326' date='May 26 2008, 07:56 AM']i've betting you'll be dumping those sp8000s in a very short time - worst tire i ever drove on - no grip - wore like nails though



after carefully inspecting the tires for signs of age and wear, drop the pressure on those tires - they have a very stiff sidewall and a hard compound - i'd start at about 33 and go down from there - you may end up as low as 28 - use the chalk or shoe polish method for sure too[/quote]



Well, the car came with these Dunlops when I purchased her. I tried a set of Michelin PS two years ago, but they were nothing like I expected after paying what I did for them, so the Dunlops went back on and they seem better. Both tires aren't that great in the wet after they're worn in a bit. The Dunlops seem to stick very well in the dry and cornering, but if there are better tires for this car, I'd welcome all recommendations. I have to defer to everyone else's knowledge since this is my first 968 and I've not had the chance to experiment with different tires. The timing is perfect: I will need new tires after this season. What would you recommend - car gets driven in a spirited manner on weekends, a few AX a season and the odd day to the office. Looking for grip, no noise, and longevity in that order. TIA

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[968crazy]

[quote name='stewhatch' post='53368' date='May 26 2008, 11:01 PM']Well, the car came with these Dunlops when I purchased her. I tried a set of Michelin PS two years ago, but they were nothing like I expected after paying what I did for them, so the Dunlops went back on and they seem better. Both tires aren't that great in the wet after they're worn in a bit. The Dunlops seem to stick very well in the dry and cornering, but if there are better tires for this car, I'd welcome all recommendations. I have to defer to everyone else's knowledge since this is my first 968 and I've not had the chance to experiment with different tires. The timing is perfect: I will need new tires after this season. What would you recommend - car gets driven in a spirited manner on weekends, a few AX a season and the odd day to the office. Looking for grip, no noise, and longevity in that order. TIA[/quote]



bridgestone RE01R they will give you best grip out of the street tires when autocrossed. The Tirerack has your sizes $120 for fronts and $128 for rears. Great tire if you dont drive it tons of miles

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[stewhatch]

[quote name='968crazy' post='53378' date='May 27 2008, 05:00 AM']bridgestone RE01R they will give you best grip out of the street tires when autocrossed. The Tirerack has your sizes $120 for fronts and $128 for rears. Great tire if you dont drive it tons of miles[/quote]

Noted. Thanks a lot. FWIW - the Dunlops I bought for the front were $66 ea. at the Tire Rack. They fit the bill

for the last two seasons hands down, but I will try the Bridgestones for next season. All four at once I assume: cannot mix 'n match tires, correct? Will these RE01R's wear quicker on the street? TIA

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