Tire Size Calculator
 

A few months ago I saw a tire calculator in Truckin'. Maybe I'm dence, but I can't seem to figure it out. If some one could explain it better I would apprieciate it

Right now I have stock 235/70-16's soon I'm going up to a 17" wheel, but want to keep my tire diameter about the same.

Troy67,
Try this one found it from someone here.
http://www.dakota-truck.net/TIRECALC/tirecalc.html
Just enter in your size then the size you are looking at and tell it to compare tire A to tire B. The table will show height width overall diameter and speedo error.
Jim

Thanks
 

Jim A, Thank you. My new tire size will be 275/55-17, about 1.5" wider and 1/2" shorter. Very cool.

Quick Size Calculations
 

Multiply your wheel width by the series value. Divide this number by 25.5. Multiply it by two. Add the wheel diameter.

This method will get you to within a thenth of an inch of the actual diamater.

275/50/20 tires

275 x 50 = 137.5 (gives you sidewall height in mm)

137.5 / 25.5 = 5.39 (gives you sidewall height in inches)

5.39 x 2 = 10.78 (gives you overall sidewall)

10.78 + 20 = 30.78 (entire diameter of wheel and tire)

http://www.miata.net/garage/tirecalc.html

Try that, it'll evn tell you how much your speedo will be off if you change sizes