MachSchnell

I'm looking at a set of cupI style 17" wheels, but they've been fitted with 235 front and 275 rear on 17x7 and 17x9 rims...now, that to me seems a bit too much tire width for the rims...am I wrong...has anyone messed around with these sizes? I would be of the opinion that 225 would be the absolute biggest to go on 7" 17s and 255 on 9" 17s...anybody care to share experiences with these sizes? or thoughts/theories?

Christer

Jason, I think I agree with you. I mean, it would be possible to mount them, but whether you get any benefit by going that much wider is highly questionable, IMHO.

AES

Check w/ the tire manufacturers websites, they list the acceptable and recommended wheel widths. For BS SO3 the 7" is too narrow for a 239/45 but the 9" is the narrowest acceptable for the 275/45

Tom W

I run 225 fron and 275 rear on 7 and 9x17" cup rims without issue. 7.5" fronts would be better, but according to the charts on the tirerack web site, the 225's on the a 7 inch rim is fine. This is for Kumho Ecsta V700 tires. You need to check for the tire you want to use.

kary993

Jason,

This really does depend upon the manufacturer of the tire. You should check the charts for that manufacturer as has been mentioned. When I used to run 17" 7" and 9" cups I never ran anything more than 225's in front (hoosiers & Kumho's). I am not aware of any 235's or 245's that would fit on a 7" as recommended. I normally ran 255's on the rear as well but when I was in the transition to new wheels I did run some 275's on a 9" cup. They did work just fine. The issue with this is that a 225/275 combo just amplifies understeer on these cars so a 225/255 is better from an overall handling perspective until you are ready for some new wheels that can handle larger sizes.

Tom W

I would also second Kary's view of 225/255 being a better way to go (with stock suspension) if you had a 993. My car suffered from massive understeer with this combination of tires - to the extent that the fronts wore out before the rears! Now this was at least partially due to my lack of camber up front (only -0.5) but stock US 993's all understeer. I am in the process of switching to PSS-9's with RS-sway bars so that I can lower the car to get more camber and adjust the shocks and sway bars to reduce the understeer.

I did see that your car is not a 993 and I know from talking with my autocross instructors that late 80's models and 964's do not understeer as much as the 993's. So I don't know that the 225/275 would be all that bad for your car. In any case, 235 is probably too big. Check the manufacturer's recommendations on tirerack for your specific tires.

GaryK

I agree as well. I can see running a much larger rear tire on the rear-engine cars, but on the 944 chassis it seems the best balance is with similar section widths of the front/rear tires.
Many of the 951's on the track here run 245/45-16's all around with 8" wheels. For 17's, I think a 245/40 front and 255/40 rear combination would work great, but you really need a 8" front rim to do this. With a 7" rim, anything wider than 225 is not optimal.