Measuring a Tire's Static Loaded Radius

Measuring a Tire's Loaded Radius

This procedure is only necessary when diagnosing trailer tire speed related vibrations or when checking the accuracy of a speedometer.

NOTICE: A tire's static (not moving) radius is only accurate while the vehicle is stopped. A static loaded radius is typically about 44% of the static loaded diameter. As the vehicle speed increases, centrifugal force causes the tire to grow taller. This force will increase the tire's dynamic (changes while moving) radius. At 45 mph, most tires will have a radius that is very close 48% tire's static loaded diameter. This growth will increase with vehicle speed and can actually exceed half of the tires static loaded diameter. The static loaded diameter is NOT the same thing as an static unloaded diameter. The example shown below shows a static loaded diameter check.

When measuring a tire's radius, use the following as an estimate:

Enter 44% (Loaded diameter x 0.44) of the static loaded diameter if the vehicle is driven at 0-10 mph while testing.
Enter 45% (Loaded diameter x 0.45) of the static loaded diameter if the vehicle is driven at 10-20 mph while testing.
Enter 46% (Loaded diameter x 0.46) of the static loaded diameter if the vehicle is driven at 20-30 mph while testing.
Enter 47% (Loaded diameter x 0.47) of the static loaded diameter if the vehicle is driven at 30-40 mph while testing.
Enter 48% (Loaded diameter x 0.48) of the static loaded diameter if the vehicle is driven at 40-50 mph while testing.
Enter 49% (Loaded diameter x 0.49) of the static loaded diameter if the vehicle is driven at 50-60 mph while testing.
Enter 50% (Loaded diameter x 0.50) of the static loaded diameter if the vehicle is driven at 60-70 mph while testing.
Enter 51% (Loaded diameter x 0.51) of the static loaded diameter if the vehicle is driven at 70-80 mph while testing.

Measure the static loaded radius between the center of the wheel and the floor with the vehicle's weight on the tire. The static loaded radius of a tire is usually less than half of the tire's diameter.

Example: The tire's diameter is 29.3"; however, the static loaded radius is only 13.1".

This page was last modified Tuesday, June 10, 2008 12:45:45 AM