What is the formula that is used to determine the O.D. of a tire. Using 245/60 15:

The tire width is about 10"
60% of 245 = 147 or 6"
6" X 2 + 15" = a 27" O.D.?

I am assuming that there are about 24.5 millimeters in an inch.

If this is correct, please congratulate me. If I'm wrong, please tell me what is wrong and how to fix it.

I went to a local tire store that was open today and the guy took put a tire on the counter and measured it. That would give me thae answer but if I'm trying to figure out what size tire I need . . . He ended up trying to sell me tires. I said, dude, I don't even have rims on it.

Thanks,
SPK

 

245/60/15

245 is the width in millimeters, and there are 25.4 mm per inch.

Multiply width by by series (in your case, 60). Multiply that by 2. Convert that number to inches by dividing your number by 25.4. Add in the wheel size (in your case, 15")

So, in a formula, it looks like this:

[{(245*.60)*2}/25.4]+15 = 26.57" tall.


I have 335/30/18's.

[{(335* .30)*2}/25.4] + 18 = 25.9" tall.

 

Sweet, thanks.
SPK

 

This is a very easy to use calculator for automotive formulas.

http://murray.faithweb.com/formulas.htm#find_rear