Quote:
Originally Posted by some_other_dave
Pedantry follows:
Sprung mass is anything that is supported by the suspension springs. The seats, the engine, almost all of the car is sprung mass. Some of the things that make up that sprung mass also rotate, such as the engine's crankshaft, the flywheel, etc.
Unsprung mass is anything that is not supported by the springs of the suspension. Things like the wheels and tires, the brake calipers, and so on. Obviously much of that mass does rotate (wheels, tires, brake rotors), but some of it does not (brake calipers, the housing of a live rear axle).
Some parts are partly sprung, like the springs themselves, suspension arms, and drive shaft(s).
Car makers generally try to reduce unsprung mass as much as they reasonably can, as it tends to have a sizeable effect on the ride quality of a vehicle.
-soD
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You are 100% correct. I did not mention the distinction only because I wanted to focus specifically on the rotational mass. I should have used "static" as the counterpoint. Most of the mass I am talking about is also unsprung, but you are right, some of it, technically, is not (e.g., the driveshaft which is actually supported by the body/frame).
There is also quite a bit of unsprung mass that can be removed from the car, but since those parts tend to be more costly to replace and still act much more like the static mass (albeit to a greater degree) than rotational mass, I'm less interested in addressing them.... for now.