http://www.redrock4x4.com/tireconve...h=12.50&stxtRim=16&submitButtonName=Calculate this is a good one that doesnt beat around the bush tryin to sell you tires if you wanna know how the metric system works: ex-285/75/16 1st number: tread width in millimeters (285mm) 2nd number: sidewall height as a percentage of width (285x.75=sidewall height) 3rd number: rim size tire diameter=3rd number x 2(2nd number) 285/75/16=32.8/11.2/16 or reasonably speaking 33/11/16.
i used this one it can convert both ways and then you can also check gear size http://www.dakota-truck.net/TIRECALC/tirecalc.html
There is also a Iphone app called tire math. It does gear ratio, speedometer, odometer, and tire converter