Hi. This issue came up in another board but it's important enough
to list again here. Anyone who needs to worry about
accurate tire diameters, or any other tire dimension should know:

Beware of those 'tire calculators' that you can find online. The creators
are certainly trying to be helpful, but they can never really do what they
hope to do, because they rely on the tire size numbers being accurate,
and they are NOT. For instance, a 245-45-16 tire is nominally a 245mm
wide tire, with a sidewall height of (245mm * .45). This would seem to
lend itself to elementary calculations. However, the actual tire dimensions
are sometimes significantly different, so one tire may fit (or have the
right diameter) when another tire of the same nominal designation will
not. The only place to get accurate numbers for tire dimensions is in the
tire manufacturers published tire specs. I have seen two similarly 'sized'
tires differ by a half inch in diameter *FROM THE SAME MANUFACTURER*.
These were just different *models* of a 245-45-16 tire.
Joe

 

i totally agree with you on your comment joe...

when i was buying replacement tires on my clk320 two different brands with supposed same tire width i was shoehorning 265/35/18 on the rears of my clk. i had a set of 18x10 sl 2piece wheel on it.

the pirelli 265/35/18 would fit perfectly without rubbing while the other brand( cant remember what it is) with the same supposed size 265/35/18 but when they put it on the car the tires would rub...

only then didi i find out that the sizes from different manufacturers are not necessarily the same

 

Isn't that the case with "like sized" 315 19" from AVS and Conti. The conti requires rolled fenders where the AVS does not?

Lou

 

Basically true, although depending on wheel offset and car hieght, you might not need to roll the fenders with either tire.