Did you find actual data showing it’s effectively 8 pounds? If so, I’d like the link. I can’t remember exactly what that number is. I thought it was about 50% of the total weight was considered rotational. But that was back in 1988 so I may be foggy on that.
And IIRC, that 50% wasn’t set in stone. It was affected by the actual diameter and thickness you can make the damper and what is needed to control the harmonics.
Interestingly enough is that even the stiffness of the crank affects what the torsional vibrations of the crank are. So...if you go from say a stock cast crank to a 4340 non twist forging, even with the same stroke and Bob weight, the resonance frequency will change, and if you are using an elastomer type damper, which has a very narrow range of dampening you have now made that damper at the least less effective.
Like I said, the science behind resonance frequency and all that is very interesting.
