[n00bim2015]

I'm terribly new to tire selection. How do you infer the tire diameter of a wider wheel. So going from stock to a wider wheel will definitely change a whole slew of specs. But Ive heard it can change your real world odometer readings. Yes no tell me more bimmerfans.

[floydarogers]

Originally Posted by n00bim2015

I'm terribly new to tire selection. How do you infer the tire diameter of a wider wheel. So going from stock to a wider wheel will definitely change a whole slew of specs. But Ive heard it can change your real world odometer readings. Yes no tell me more bimmerfans.

Start here: http://www.tirerack.com/tires/tirete....jsp?techid=46

Remember your math: 225/40R18 means tread width is 225mm, /40 is the aspect ratio - this means that the tire's sidewall is 40% of the width, and 18 is the wheel size in inches it fits on. (225 * 0.4) * 2 + (18 * 2.54) gives the nominal diameter, in mm, of the tire.

A taller tire makes fewer revolutions (greater circumference), so throws off the speedometer. As does a shorter tire go the other way.