Porsche spec is different for the 987

I am having a set of 18" Super Sports put on my 01 Boxster today. They come highly recommended, does anyone have any experience with these tires? Any suggestions for tire pressures? Thanks for any help.

Terrific tires. Had them on my 02S. Very quiet and great performance. Michelin is replacing them with the PIlot Sport 4, I believe. IIRC, i ran 32/34 for air pressure.

Stock, quiet, decent wear, good in wet. I have them on my S6, and drove them on an AX student's car yesterday.

As with everything, there is no best tire. Its likely the best "jack of all trades, super high performance" tire i know of.

G

Grant

gee-lenahan-at-gee-mail-dot-com

Porsche specify 29F, 36R. This results in terminal under steer, presumably to make sure they are dumbed down for the masses.

I run 33R/31F on the street, and very similar (hot) on the track (32/31, or 33/32).

I know that our local high-end tire shop (one of the partners/brothers regular job is on-site tire and suspension engineer for United PSorts Car racing - was Grand Am) sets them to 32 square on 986 boxsters with 17" wheels. At first I balked, then i learned :-)

So up the fronts and down the rears.

YMMV

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Grant, do you consider your pressure - 33R/31F - to be optimal for handling or for wear/milage or both?

... or they correlate (wear = handling) because my wear is always due to outside edge wear, caused by hard (very) cornering.

Maintaining optimal grip means optimal contact patch which, in the end, means optimal wear.

Now, under light loads that might be different. But i suspect the differences will be small. Lightly driven, and highway driven, cars wear the inner edge of the rear tires first due to the negative camber. My settings are so far off stock its not a good comparison.

That said, my tires, given their abuse, last very well. I'm on my third year for my street/everyday + autocross car, on very soft competition tires: Bridgestone RE71-Rs. They may cycle out before they wear out.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

How does reducing rear pressure decrease understeer other than by reducing rear-end traction?

(track discussion, not necessarily street)

There is generally one pressure where a) the contact patch is maximum, b) pressure is most consistent across it, and c) temperatures are in the sweet spot. I have generally found that with street-legal but sticky (Toyo 888, RE71R, A008R etc), as one goes much above 35/36 psi they can get greasy and lose traction. I have been slowly reducing the pressure to find the optimum spot and have settled in the 33 psi range for the rear. Quite a few racers and Porsche tech experts (Pete Tremper, Simon Kirkby) have advised me to lower them from the 38/36 where i was. It does appear to be better, but of course, one has to be careful cold since there is not much stability (they may be as low as 27-28).

On the street, similarly, i have found that both wear and rear-end stability feel just a smidge better a pound or two lower than Porsche's recommendation of 36. Below 32 they clearly get squirrelly, likely sidewall flex or worse - running slightly on the two outer edges.

On track success has a large component of temperature. On the street i presume its more of a pure pressure issue.

The physics and materials science of tire adhesion get complicated pretty quickly, but I feel comfortable simply saying that even the rear does have a slip angle associated with it, so lowering the rear will have an impact on under/oversteer -- but that's not necessarily why i suggested dropping them 2 PSI. It was a) inference from track experience (maybe dicey) and b) empirical.

Grant

gee-lenahan-at-gee-mail-dot-com

If reducing rear pressure increases rear adhesion then wouldn't that increase understeer?

and will manage understeer/oversteer. The Porsche spec (front) is apparently to dial in understeer and out overstreer.

This is all educated speculation of course, Porsche does not come out and say that.
In fact on track i am switching to a "square" setup (rear wheels and tire sizes all around) to put and end to it.
G

Grant

gee-lenahan-at-gee-mail-dot-com

Grant - are your street number cold, and your track #'s hot?

>> I run 33R/31F on the street, and very similar (hot) on the track (32/31, or 33/32).

Street temps don't rise nearly as much.

I only discuss hot track pressure.
Discussing cold pressure is senseless since that means we all guess how much they will rise, and i assure you I'll always guess wrong.

Once i get my hot pressure set, i simply don't touch them. I let them fall to where they will, and once they heat up, return to proper operating temperature.

G

Grant

gee-lenahan-at-gee-mail-dot-com

I just had a complete set of Pilot Super Sports installed by the dealer, and the readout on the panel is 30 front and 31 rear when cold. I checked the door sticker, and sure enough, that's the spec for my car.

Thanks everybody for your insight, the tires are on now and I have initially set them at 32F/34R. I am sure I will play with this. Seems to me at the track I ended up running 32 all round but that was a while ago. Thanks for your help.

don't forget that they can be a bit slippery for the first few hundred km until the mold release wears off of them. i have found it particularly noticeable on hard braking.

--
MY 2000 S, Ocean Blue, Metropol Blue, Savanah Beige.
Bought June 2000 - Sold May 2010