Useful on-line tyre size calculator

[Fastbrit]

Just discovered this useful on-line resource that allows you to calculate tyre diameter etc – it even goes down as skinny as 135 x 15...

http://www.tyresave.co.uk/tyresize.html

[Zach Gomulka]

You can also figure out tire diameter with some simple math... Say you have a 205/70/15 and you need to know the diameter in inches. First take 205 and divide by 25.4 to convert millimeters to inches = 8.07". Next, multiply that by the aspect ratio, in this case it is 70%, or .7 = 5.65". That will give you the height of one sidewall. Now since 2 sidewalls make up the diameter of a tire, multiply that by 2 = 11.3". Add in the diameter of your wheel, 15", and you have 26.3", the mathematical diameter of a 205/70/15.

[Fastbrit]

Zach, I know... but how much quicker is it to select three numbers and hit a 'button'!