Peter, physics was never my strong point. I am more into drugs!! BUT. The mass of the cast iron drums plus steel brake plates as opposed to the steel/alloy rims needs to be taken into account. That will take serious computations that a) I can't recall and b) I don't want to. All I can say is the 21" front wheel on my Rapide is a joy and everone who has ridden it are impressed with the light turning/steering on Australian roads.Would I be correct in assuming that the nearer the mass to the centre of rotation, a lesser gyroscopic effect will be incurred, in other words the brake drums will have a lesser gyroscopic effect than the rim, inner tube, tyre, spoke nipples etc.