Hi,

The best way is to test a car or motorcycle you know the power of and adjust the moment of inertia so it matches. Alternatively can also try to measure with a rope around the roller a few times then through a pulley in the ceiling where a weight is hanging. Then you time the fall of the weight and calculate MOI from there. But there are inaccuracies with friction of the pulley, etc. 

You can of course also try to calculate the MOI. There are calculators online. You need to add the MOI of the car/motorcycle if you are after motor power. 

Thanks for you answer.

I’ve a inertia dynamometer 2wd, 4 rollers type, each roller diameter 300mm and length 700mm, weight is 200kg per roller, may I know what is the maximum engine horsepower can be test?

Hi,

Each roller has a MOI of 2.25 kg*m^2, so 9 kg*m^2 in total. 

There is no fixed max number, but the runs get faster and faster to a point where you will lose accuracy. 200hp will be no problem, you can probably go higher. 

See attached file where you can play with numbers.