Ground Clearance Change Calculator

How we calculate

Enter the current tire size and the new tire size. The calculator shows both nominal outside diameters and the change in ground clearance under the axle, in inches and millimeters. A positive result means more clearance, and a negative result means less. Metric sizes such as 265/70R17 and flotation sizes such as 35x12.50R17 are accepted.

How we calculate: the axle sits at the center of the wheel, so its height above the ground is half the tire diameter. When the diameter changes, the axle moves by half of that change. Clearance change equals the new diameter minus the original diameter, divided by two. Metric diameter in millimeters is the rim diameter times 25.4 plus two times the width times the aspect ratio divided by 100. We divide millimeters by 25.4 for inches.

For example, going from a nominal 31-inch tire to a nominal 33-inch tire adds 2 inches of diameter and 1 inch, or 25.4 mm, of clearance under the axle. Going from 265/70R17 to 285/70R17 adds 2 x 20 x 0.70 = 28 mm of diameter, so the clearance change is 14 mm, about 0.55 inch.

Under this model, everything carried by the tires rises or falls by the same amount: the axle, the suspension, and the body. Bumpers and rocker panels move by the same figure, and approach and departure angles change as well. The loaded radius is smaller than half the nominal diameter because the tire flattens under weight. Load, inflation, and construction affect it, so measured clearance can differ from this nominal figure.

A larger tire also needs room in the wheel well when the suspension compresses and the wheels steer. It changes speedometer and odometer readings and gearing, and it can affect stability control. This calculator does not check fitment. Measure the available space, read the vehicle maker's tire guidance, and ask an installer before changing size.

Frequently asked questions