Rolling radius is an important parameter for tyre testing, as it helps to assess the performance of the tyre when it is in motion. Rolling radius is a measure of how far the tyre will roll in a given distance. Static rolling radius is the radius of the tyre when it is stationary, while dynamic rolling radius is the radius of the tyre when it is in motion. The data on rolling radius is needed to accurately compare the performance of different tyres, as well as to determine the best tyre for a given situation

Radius depends on tire profile and load, and speed, because a wave may build ahead of contact patch increasing effective radius. Also, at very high speed, tire grows in radius, much like a tire used on a dragster race car. For low speeds you can do a roll-out: mark the tire and the ground, roll forward one revolution and mark the spot. The distance noted is one Diameter X Pi (3.1416). Divide by 2Pi for the radius.