Hank Cohn

Mitch,

Rereading the ‘brakes’ thread, I am curious if you would get an ABS fault if the problem lies with front to rear tire diameters being outside of the ABS computer’s expected parameters - especially under maximum or near maximum braking? It seems likely that there would be a fault but, perhaps, the ABS system is just doing its job and releasing brake pressure on the wheel(s) turning slower than it would expect relative to the other wheels’ speeds and its programming.

It sounds like you are married to the MPSCs, but, if not; Hoosier and Toyo offer 18” tires in very very similar diameters as compared to stock. While it could be tuned out, a 345 sized tire would surely add more understeer to the car.

I have used and enjoyed MPSCs for years but they are just not available in compatible 18” sizes. I doubt they will add a tire to the lineup as it has been relatively static for years.

I have a track weekend coming up in a few weeks and am struggling as to which of the two aforementioned tires to purchase. It sounds like the Hoosiers are more similar to the stock tires with regards to hot inflation pressures and sidewall stiffness.

Thanks for the update and please post any additional findings.

Thanks,
Hank

mitch236

Which Hoosiers would you be using as I can't find an R-6 size combo that works.

ABS wouldn't give a fault because as you said, it is just doing its job. I love the MPSC's but will probably go with Hoosiers if I can get the problem solved. You would think Porsche would make it easily possible to alter the ABS diameters with PIWIS.

eclou

for the R6's run 245/35/18 (24.8") front and 315/30/18 (25.6") rear. You can also use 305/645/18 VRL (Viper Racing League) Hoosiers on the rear. They are the same compound as the R6 and are the same effective size as a 305/30/18. These tires have slightly smaller diameters than stock but IDENTICAL effective ratio front to rear. I have no problems tracking my TT with these tires - no PASM, PSM, ABS faults.

While MPSC's are fine, I don't understand buying a $100k+ car and running it on the track with anything less than the best tires available. Same principle as when I see people out at my range with $3K+ "sniper" rifles shooting factory boxed ammunition and wondering why they aren't shooting sub-MOA.

mitch236

For me it comes down to convenience. I don't want to have to deal with the tires on a regular basis. Based on previous experience with MPSC's, they will last 10-14 days. But it seems I was (easily) convinced to run slicks. I'll be at Sebring in a week and a half and will report back my findings. I should be able to run in the mid 20's with slicks. That will be fun.

eclou

Mitch did you ever get this resolved? Bob Rouleau also observed this phenomenon on someone else's GT3 with oddball tire sizes