The mass is not the most crucial paramter, it is the moment of inertia that is most important for a wheel. The further the mass is from the centre of the wheel, the more influential it is. This is governed by a square rule. There is therefore much more interest to me in reducing the amount of material near the rim than ornately removing material from the spokes near the axle. In this sense the plastic refurb jobs become more appealing. As the outer material is less dense
back of the envelope calculations tell me that for a uniform sprocket, it has half as much energy in the form of rotational energy over and above what it had from its travel in a straight line.
The fact that these sprockets have most of their mass on the outside means the figure is likely to be greater. But its hard to tell without the cad file.
Anyone who is into pedal bikes knows that the shape of aluminium items are very different to steel even though they do the same thing. I see these steel sprockets have thin spokes and there fore must have a higher proportion of their mass on the outside. hence the added weight of steel preludes to a much worse problem of weight distribution.
