Calculators Metric Tyre Height

Knowing the mounted height of a tyre is important to figuring overall gear ratios and engine rpms , especially when changing to larger tyres. The metric numbers don't make that easy but there is a formula for calculating the height of a metric tyre.

Use the form below to enter the values you require. Bear in mind that the actual mounted height might be somewhat different than the formula shows. Tyre manufacturers can supply very detailed specs on it's tyres.

Section Width mm Aspect Ratio mm Rim Diameter inches   Tyre Diameter mm Tyre Diameter inches

For those that prefer to do it manually or require the calculation when not at a computer, the following describes how it works, with an example.

Tyre Diameter = 2 x Section Width x Aspect Ratio 2540 + Rim Diameter

In the case of a 235/75R-15, the formula would look like this:

28.88 inches = 2 x 235 x 75 2540 + 15

Light truck metric tyres commonly come in 70, 75, 80 and 85 aspect ratios. A 235/85R-16 (31.7 inches) and a 265/75R-16 (31.6 inches) are nearly the same height but the 265 is about an inch and a half wider. You can convert millimeters to inches by dividing by 25.4.

© 1998-2013 Martin Wittenburg and Michael Wittenburg. All rights reserved.