Sprung weight vs unsprung weight.

I don't agree with the idea of parts being x percentage sprung and unsprung, that sounds suspiciously like engineering approximation for calculations.

Think of unsprung weight as any mass that has movement controlled by a spring. This is suspension, valves, etc. And the assumption is that the body of the car is not moving in reaction to things.

High unsprung weight scenario: you hit a bump. The tire leaves the road. It's going to take longer for a given spring to get that heavy tire back down to the road and get you back in control of whatever it was that tire was doing.

The other side is, you hit that bump, it takes more energy to move that tire to react to that bump. If the spring isn't absorbing that energy (because it's too stiff for the given impact), it's being transmitted to your car (aka you) as a bump or jolt. Soft spring to absorb energy and give nice ride doesn't control the wheel properly. Stiff spring to control doesn't ride well. Reduce the unsprung mass, and the two springs become closer to being the same spring.

ROTATIONAL mass is typically the one where x pounds rotational is worth y pounds non rotational.
This is because the energy needed to accelerate the weight in rotation is reduced, giving an increase in acceleration equal to the acceleration gained by losing a certain amount of fixed weight in the car.
I want to say one pound of rotational weight is worth four in the car. Lose ten pounds off each tire and it's like you dropped forty out of the car.

This is a two-for, less weight overall AND less rotational weight to spin up. All the above are factors of total overall vehicle weight. Ten pounds on a three Hundy pound sport bike is instantly noticeable. on a three ton tank, not so much.

There is probably some way to relate sprung and unsprung mass equivalents, but I don't know what it is. these pay off in acceleration, braking, cornerning, anywhere traction is the action.