I just took some rough data from the flywheel shown in one of my posts in the RC Benchmark thread. It weighs 458g, and has an OD of about 2.25" (the weight is not evenly distributed across the disk). I ran it using a 21.5 motor on 1s LiPo with 23T/44T 32 pitch gears (a 1.91:1 reduction of speed from motor to flywheel).

My initial target was to have sufficient effective MOI to get about a 1% change in velocity between readings (one reading per revolution) at the motor's power peak (which occurs at about 50% of the free-running speed). Modeling showed that requires about 40 total motor revolutions with the required MOI.

The data showed that the motor reached 50% speed after about 4 revolutions, or a factor of 10 less than desired. If I change the gear ratio to 1:1, that gains me a factor of about 3.66 (1.91^2). That means the flywheel MOI must increase by a factor of 2.73 to get me where I want to be. Time to try a larger flywheel!