A simple study of some Applied Physics will always win over intuition driven or "some guy said" approaches. The matter of rotational inertia or inertia in general certainly falls in the problematic area. What Dwight has suggested is absolutely correct. Not just the mass of the item but where the mass is concentrated is most important and that is referred to as the radius of gyration on rotating components. The rotational inertia of parts can be measured by using a homemade torsional pendulum. The measurement is often easier than more complex calculations and is certainly more accurate. So doing things in this manner quite often is a bubble burster, but finding the actual truth will not only help your racing program but also save you some money in the process.
Regards,
HB2
Dissident