AutoX924S

Hi. My dad and I have been arguing over this question for awhile now. We have a red 1988 924S with 16" Boxster wheels and 205/55/16 tires in the front and 225/50/16s in the back. I was wondering exactly how much range you have on tires sizes on different rims. Like for instance, can you fit small 205 tires on an 8-inch wheel? Is that too much? Or say a 205s on a 7-inch wheel. I know 25.4 mm is an inch so that would mean that every 25.4 mm of tire is an inch of wheel. The reason I am asking this is because we are looking at getting track wheels and tires and many of the nice track wheels that would fit our car are 8 inches on the back. As you probably know it is VERY hard to fit 8-inch wheels on a 924S or most any 924. Most of the time when wheels rub, it’s not the wheel itself that rubs; it’s the tire. So I was wondering if you could put a 225 tire on an 8-inch wheel and not have it make any difference in handling or wear. I heard that drifters take really wide wheels and put small tires on them to prevent tire rolling. (PIC BELOW) I don’t want to make the tire small to that extent, but just so it will either be just even with the wheel or a little bit inside of the wheel. Will this work?

My other question is about tire height. My dad thinks that if you have a smaller series tire (i.e. 30 series tire) it would have much more tire wear. I thought that it wouldn’t make any difference about how tall the tire was because the thickness of the tire does not change when you get a smaller series. It only changes the sidewall height... right? I thought this was right but he keeps arguing with me. Well thanks for reading all my questions!

Bye!



-Adam

Bill Gregory

Adam,

You probably should consult the manufacturers recommendation on wheel width. For example, in the Michelin Cup tires and Toyo RA1 (both r compound), 225x16's fit on 6" to 8" rims. The benefit of fitting a tire to a larger rim, ie the 225 on an 8" rim, is that the sidewalls are pushed out, hence they are stiffer and more responsive. Michelin even recommends for their Cup tires to mount them on as wide a rim as possible. Looking at the Michelin Cup and Toyo RA1's in 205x16's, they can fit on 5.5"-7.5" rims.

You'll probably want R compound tires for the track, and both the Michelin Cup and Toyo RA1's are two of the longer wearing track tires. A pretty good track tire summary is here.

AutoX924S

Thanks alot Bill! And about the lower profile tires? I heard that smaller profile tires are stiffer and they turn faster. Is this true? Feel free to add any info you know... im trying to learn so any more info is good!

A930Rocket

Yes, but at the cost of a firmer ride. For me? That's OK.

earlyapex

Grassroots Motorsports tested +1, +2 wheel/tire combinations versus stock a few years ago. The +1 and +2 wheel/tire combinations were faster on track. There's always something you give up though. Ride will degrade and your expensive wheels will be more susceptible to damage with lower profile tires. You also have to take in consideration the rules governing your events and what they allow. You can easily fit 225's on 8 inch wide wheels. As you have stated this size wheeltire is a tight fit in your type of Porsche so you may have to go to 205's. If you're limited to 205's in the rear, then consider 7 inch wide wheels, which should weigh and cost less. Tire wear has more to do with rubber compound, type of car and usage than side wall height.

MitchB

A good resource you might consider is looking at the Tire Rack website - tirerack.com - maybe?
Anyway it has a huge "Specs" area for each tire with all the info you need...
It's a place to start.