Hi
@ColoradoGuy I don't remember offhand the exact ratio, but there's a multiplier on rotational vs static mass. I want to say it's around 3x or so, although that may vary depending on the specific use case. The thing is it ends up being a significant amount more than the static weight of the object would indicate, because you are removing inertia from a moving part. So it's a fairly sizeable gain, even with relatively modest masses.
It's a legitimate thing to look into. It's the reason folks focus so much on things like lighter wheels, because it's not just the weight of the old wheels minus the weight of the new ones, it's more like: savings=3(old_weight-new_weight). Or something close to that.
EDIT: It's actually much more complicated than that. I did find a handy calculator you can use, though, if you're curious. I don't have any connection to the calculator, it's just something I found online, but I thought it might be helpful:
The Effects of Rotational Inertia on Automotive Acceleration