Tire Size Question
 

I have an 89S2 with aftermarket wheels. 7x17 F and 9x17 R. Currently the tire sizes are 205/50 17 F and 255/40 17 R. Could I replace the fronts with 215/50 17 and leave the rears 255/40 17? Thanks.

Your current front size is the 'optional' 17" size recommended by Tire Rack. Considering that a 205mm tire should have a sectional width of 8", and a 215 would be close to 8.5", I'd think that the side walls might bulge out too far, and look kind of funny. You'd be better off with an 8" or 8.5" front wheel.

Personally, I'd stick with the 205.

I was going to mention the tire diameter mismatch on ABS cars, but I looked it up and it won't be a problem. The Owner's Manual (p32) says a difference in rolling radius more than 17% deactivates the ABS. Does that mean 17% front to rear or 17% from stock?

Not that it matters much. 17% is huge.

as a reference, the stock wheels on the 968 are 7.5 and 9 x 17 - stock tire size is 225/45 and 255/40 respectively - same for bmw 3 series

so, yes, a 215 is fine, and in fact, however, you should drop to a 45 series, as the outside diameter will be pretty large otherwise - we know plenty of guys successfully running a 225/45 on a 7 on the street

Your 205/255 setup is a recipe for understeer.

I'd go with 225 on the fronts. They will bulge some on a 7" wheel, but that's what I use for racing my NA.

A wider front will follow any imperfections in the road surface, and the steering will be a bit heavier than with 205s. I think it's well worth it for the greatly improved handling.

My old S2 originally came with 225/245 tires. Going skinnier in front, and wider in the back will hurt the factory handling characteristics.

The 205/255 setup you have was used by the factory for a few years on the 911, to compensate for that car's heavy weight bias towards the rear. A 944 is most fun to drive with equally sized tires both front and rear.

I prefer to run equal size tires for autocross and set the car up to be very loose. Then I run staggered tires for the street to make it more stable.

The S2 came from the factory with staggered tires. 205/55/16 and 225/50/60 for my '89.