sten gr

What tire size is recommended on a 964 rs M003 ?
I have a almost new but slightly used set of MPSC in 235/40 18 and 295/30 18 witch followed when I purchased a set off BBS mag’s The rear rims were 11” so it didn’t fit (actually it fits on one side) I changed the outer part and got 10, 5” and put on 285 Hoosier s04, and there might be space for a bit more.
When I compare the tread width on the Hoosier and Michelin it looks like the MPSC are much wider and wouldn’t fit?
But the main question is do I really need this wide tires on a light car? In Norway we are only running 15min sprint races, and the air temp is normaly between 15 and 25 deg. C
Last year I was running on 265/35 18, it’s still some laps left in them, so I wonder should I sell the extra wide 235 and 295 MPSC and by a new set 225 and 265,or try them on.
Please feel free to advice the best size for my 1100 kg 306 hp car

Sten

ltc

Have you considered running either of the wheels (17" or 18") used on the Carrera Cup cars?

http://cupcar.net/92cup.asp
Wheels/Tires
Used 8x17" front and 9.5x17" rear one-piece Cup wheels
Used 8x18" front and 9.5x18" rear three-piece "Speedline for Porsche" wheels

Recently discussed:
https://rennlist.com/forums/wheel-and-tire-forum/342632-do-wb-964-cup-i-s-fit-nb-964-without-spacers.html

Geoffrey

Based on some tire testing we've just completed on a 964 Cup, the wider tires are not faster than a smaller size, and may actually be slower on a tight track. If it were me, I would look for a 235 slick front size tire and a 265 size rear slick. This will translate to a larger size in the R compound, probably something like 245/275. I'd stick with 8.5" front and 10" rear rims.

I would favor the Hoosier over the MPSC which likes more camber and is a faster tire. The MPSC do not like colder weather, take awhile to come in to temp, and are not as sticky as the Hoosier.

sten gr

Don’t want to use the cup wheels on races, and got no descent tire in 17” Bought the car last year and got a van full of tires on top (5 sets + the tires that followed with the BBS rims) unless I have to, I am planning to use up the old ones before I by some more.

I checked the size on the BBS rims its 8,5” and 10” not 10,5”
Have to run MPSC on races YES thy do need some rounds to get the temp but it’s the same for everyone. On track days I prefer Hoosier.
Thanks for confirming my thoughts on the wide vs. smaller tire,
But anyway I have the MPSC 295/30 18 and I’m a bit lo on cash these days so I might run those tire this season, so will thy fit??? Te tread width is significantly wider than the Hoosier s04 285/30 18 any comments on this ore do I simply just have to mount them on and try?

Hello Geoffrey do you mean the Hoosier need more camber than MPSC ore the other way round?

Sten

DrJupeman

Geoffrey, in your testing how were you running anything much larger than a 265 slick on the 9.5" Cup wheels?

38D

No. You can shoehorn a 285 in the back of a narrow body 964 but no way will the 295 fit. I ran 295s in the rear of my 964 turbo and they barely fit.

DrJupeman

Who have you seen shoe-horn 285s on the 964?

Cory Jump

I have two customers who run 295/30 hoosier on the back of RSA race cars. I personally run 275 in the 17" variety which I think is most common. I have not seen any advantage of running 285 18 verses 275 18. 295 definitely will not fit.

carreracup21

I've run the 295's on my old US Cup. They had to be shimmed just right down to the mm, but they would fit. The 285's might have been a tad faster because they were smaller in diam. and gave a gearing advantage. 275's worked well also, but the 295's could really take the heat. The 295's were awesome at a track like Roebling that was very hard on tires. These were all 18 inch R5 Hoosiers

Geoffrey

I have seen 285s on narrow body cars, but that is an R compund in street measurements, not a 285 slick which would not fit.

Colin, the 964 turbo has different control arms which are the limiting factor for tire width. If you ran narrow body trailing arms on the turbo body (as all RSRs and Turbo LM cars did) you can fit a 305 slick, 335 R compound. I run a 12" wheel on my stock turbo body RSR.

sten gr

OK thank you boys, I am convinced, I was working with alignment yesterday and wanted to have some toe in on the rear wheels, I noticed it is allready polishing the oiltube with 0 toe and 285 Hoosier, and the 295 MPSC seems much wider, so now I m gonna paint them white an make $1200 flower beds out of them.
Sten