HOW DO THEY MEASURE INERTIA?
World Four-Stroke and Veteran Champion Doug Dubach is a fulltime test rider for Yamaha who just happens to own DR.D racing, which sells flywheel weights. When Dubach set out to design flywheel weights for DR.D Racing, he borrowed Yamaha’s moment of inertia tester. How does it work? A flywheel, with or without weight, is placed on a spinning platform. When the platform is wound up and released, an indicator counts how many times and how long the platform unwound and wound. Using a formula, the tester calibrates the exact moment of inertia of the flywheel. A flywheel with more inertia will take longer to wind and unwind, but it will do it more times. Although the weight was picked by using the kilogram-centimeter squared (kg-cm2) measure of the moment of inertia, Dubach still advertises his weights by gram weights. A weight is still the number that is most recognized by riders. The stock YZ45OF flywheel weighs 469 grams and has a moment of inertia of 3.6 kgcm2. Dubach offers his weld-on
