[HoodPin]

Originally Posted by FTS

Although certainly true, this is valid only if you are trying to determine camber/toe settings' effect on the tires. How would a pyro help determine optimum tire pressures (not heat distribution across the thread)?

I would believe that if highest in the center of the tread, pressures may be too high. If too low, the center should be lower than the inner/outer edges. However, suspension settings will muddy the water, too. Toe-in would heat up the outer edges; Toe-out should heat up the inner edges. Camber should cause a change across the surface. Too much negative camber and I would expect the inner edge to be highest and gradually decreasing to the outer edge. Whereas too much positive camber would do the opposite.

If everything is set perfectly, see Stephen's post below.

[Landjet]

Originally Posted by Seltzer

Larry,l

You gonna make it on the track?

I'm coming out Saturday, we'll see what happens.

[smdubovsky]

Originally Posted by HoodPin

If everything is set perfectly, the tread temp should be even across the entire surface.

Thats not true (except on the skidpad.) The slope should be even however. Due to camber and the existence of braking at the ends of straightaways, the inside will (and should) always be hotter. If tire temps are even all the way across you're giving away grip in the corners.

[HoodPin]

Originally Posted by smdubovsky

Thats not true (except on the skidpad.) The slope should be even however. Due to camber and the existence of braking at the ends of straightaways, the inside will (and should) always be hotter. If tire temps are even all the way across you're giving away grip in the corners.

Amended my post.
I haven't done much of this myself, only read about it (mostly long ago...). But your explanation makes sense.

[vranko]

I've been running R888s on my 2007 Cayman S. I try to keep them below 36 hot and usually start them at 24-26. Anything over 36 and they get very greasy. I try to target 36 when autocrossing.

[CanAm]

Originally Posted by Vicegrip

Pressures and temps are linked..

I'm wondering if the tires will still lose a lot of grip due to overheating, even if I lower the cold pressures enough that the hot pressures are near optimum. I see the pressure as mainly controlling the tire shape, whereas the temp should mainly affect the rubber properties. I guess both pressure and temp should affect how the tire responds to load (?).

Originally Posted by smdubovsky

Thats not true (except on the skidpad.) The slope should be even however. Due to camber and the existence of braking at the ends of straightaways, the inside will (and should) always be hotter. If tire temps are even all the way across you're giving away grip in the corners.

To further complicate things, seems that the tire temp patterns would also be affected by the mix of straights, left turns, and right turns, with trade-offs among them?

Originally Posted by vranko

I've been running R888s on my 2007 Cayman S. I try to keep them below 36 hot and usually start them at 24-26. Anything over 36 and they get very greasy. I try to target 36 when autocrossing.

Though you're running an R-comp vs my street tire, good to see at least partial confirmation of the ~36 number. This past weekend, I kept dropping the cold pressures and finally got down to 26, which is the lowest I've gone so far. And when the pressures got close to 40, the grip seemed to drop so much that it felt like a different car.

[Dr K]

Originally Posted by Irfan

I would have tried it this past weekend (good event with PCA Reisentoter - nice people), but the wife and I were sharing the car with her sessions coming right after mine. She cools the tires down nicely.

Actually, that's perfect. Have her meet you in the hot pits (with her instructor) to swap the car, and while they're belting themselves in, you go around and check the temps. Look at the numbers as she drives away...

[Vicegrip]

Originally Posted by Irfan

I'm wondering if the tires will still lose a lot of grip due to overheating, even if I lower the cold pressures enough that the hot pressures are near optimum. I see the pressure as mainly controlling the tire shape, whereas the temp should mainly affect the rubber properties. I guess both pressure and temp should affect how the tire responds to load (?).



To further complicate things, seems that the tire temp patterns would also be affected by the mix of straights, left turns, and right turns, with trade-offs among them?



Though you're running an R-comp vs my street tire, good to see at least partial confirmation of the ~36 number. This past weekend, I kept dropping the cold pressures and finally got down to 26, which is the lowest I've gone so far. And when the pressures got close to 40, the grip seemed to drop so much that it felt like a different car.

I only see one "cold" pressure a day on my track car and that is before I go on track in the a.m. Once I have go on track I ajust hot pressures only. there are no more cold pressures for the day. In fact if one side of the car was getting full a.m. sun the pressures will me off and I only check to see if there was a leak. I expect the sunny side tires to have a higher reading but as I don'r know the thermal gain I don't ajust and skip to the end of the run.

Come in after a session, test the pressures (and temps if ajusting more than pressures) and ajust them to the target hot pressure if needed.

Don't overthink this.

[CanAm]

Originally Posted by Dr K

Actually, that's perfect. Have her meet you in the hot pits (with her instructor) to swap the car, and while they're belting themselves in, you go around and check the temps. Look at the numbers as she drives away...

You're right, I didn't think of it that way. Switching in the hot pit is a perfect opportunity to get the temps, and then she can go out and cool the car down. Not sure what the sequence of run groups will be this weekend, but will do this if it works out. Now I'm really curious to see what the temps are.

[Baywatch]

X2 Vranko's temps are what I try to come off the track with hot. 36 seems optimal for my 888s as well. I Usually start the day at 25 - 28 and play with the pressure as the day progresses. Once they are consistently running 36 hot, simply checking them and adding air as necessary seems to do the trick. At Autocross I run the 888s with 33 in front and 36 rear granting a bit more grip at the event. No chance for them to heat up at autocross so starting at the correct pressure is the key.