Tire diameter and final drive ratio are needed to calibrate the display's speedometer and dynamometer.

The best way to measure the wheel diameter is by measuring the radius of the driven wheel, when the vehicle is on the ground so you can take into account the flex (compression) in the tire.

Measure from the ground to the center of the wheel axle – double this number – and set the resulting diameter value here.

   Tire Diameter    
       29.0 in