The mass moments of inertia of 44 mounted and unmounted passenger, racing and motorcycle tires were measured about the spin axis. In addition, for some of the unmounted tires, mass moment of inertia about an axis perpendicular to the spin axis was also measured. Simplistic models for calculation of tire mass moment of inertia were developed, and may be adequate if only approximate results are required. Following measurement of inertias using a torsional pendulum technique, linear correlation of inertia values with tire weight and diameter was performed. A simple pair of linear correlation equations (one for mounted tires, one for unmounted tires) gives highly accurate values for mass moment of inertia about the tire spin axis. Finally, a rule of thumb expression for estimating moment of inertia about a vertical axis was also developed.