Tire Size Option question

This is a email from [trottier.ed]

I am posting it for Ed

trottier.ed wrote: All--As I am sure you know, ZRi is/has discontinued its "staggered" pair for ('89 to 91) S4/GT. 225-50/16 F and 245-45-16 R. Had several discussions with Tire Rack in last month and here is what they have to offer:

Numerous choices for the 225-50/16 Front; it is the 245-45-16 rear that is "gone." Alternate size suggested is 245-50-16, which results in a number of attractive brands. HOWEVER, when I asked "what am I giving up from Porsche OEM size?" I was told that height difference is about 0.5" (4.8 to 4.3 inches), but that 245-50-16 was actually LOWER by that 0.5". Seems to me that 50% of 245 is a LARGER number (taller sidewall) than 45% of 245, but I am an amateur at this stuff. Tire Rack also opined that "This alternate size is within 3% of OEM and is thus acceptable by Porsche specifications." 3% of 4.3in = 0.13in, so it is not clear to me how a 0.5in change is within that range. HELP !!

Dose anyone have any info on tire sizes they can share with Ed

Thanks

Brad

Not sure how the calculations are being made but the error is perhaps lost going from metric to imperial.

The first number in the tyre size is the tread width expressed in millimeters so doing some basic math with the 50% available vs the OEM 45% size results in a difference of 12.2mm which is larger than the 3% at 7.35mm.

Now we have the math stated real world tyre manufacturing is not that close with sizes quite different between makers even though the rubber is stamped/molded with the same data.

My personal opinion I'd get the 50% rubber and not worry about it or upgrade to larger wheels with more available rubber.

BTW.....for everyones info the OEM sizes are available through Conti. I've a brand new set in my garage for a customer car Im working and can get my hands on another set. Let me know if anyone is interested....first come first served

Fuzion has 245/45/16's available locally in the Atlanta area. Similar to the Potenza RE 750. My understanding is they are owned by Bridgestone. I have had them on for about 6 months, no issues, price is good.
Dave

I think I need new ones too

Cool - you can even count how many nylon threads you have as the rubber shreds away .....I guess that's one way to see how well your tire is built.. HA

With a 16v we are lucky I guess in that we can rotate our tires and get all the same size. But the bigger back ones look really cool, do you 32v guys find there are issues not being able to rotate? Or once they are on and properly aligned, the car usually does a good job of even wear?

Just wondering as my son-in-law has an 83 911 with a Carrera body kit and larger rears and he asked about it.