Guides
Short explanations of the numbers behind the calculator, with the formulas and worked examples.
How to read a tire sizeWhat 265/70R17 and 35x12.50R17 mean, how the numbers turn into inches of sidewall and overall diameter, and a table of common sizes.Wheel offset and backspacing explainedWhat offset does, why a lower number pushes the wheel out, how to convert between offset and backspacing, and how to measure your own.Tire size and speedometer errorWhy bigger tires make the speedometer read low, the formula for true speed, worked examples for common swaps, and what the 3% rule means.