There has been some talk in rec.sport.snowmobiles about Titanium Jack or Drive shafts. While this is true, it isn't really the rotating mass that matters.
Rotational inertia is to rotation what mass is to linear acceleration.
Rotational inertia takes into account how far the rotating mass is from the axis of rotation. Solid round bars have very little rotational inertia because the mass is very close to the axis of rotation. W is the rotational velocity of the jackshaft in radians per second. Alpha is the rotational acceleration of the jackshaft in radians per second squared. This assumes no track slip and average acceleration between points was used.