In configuration on the last picture there realy is not much less unsprung weight but in the configuration on the first there is.
Brake disks are located near differential which is fixed to the chassies. They do not go up and down with wheels.
I don't get it, don't the discs still turn like on normal car? If so how would there be less unsprung weight?
Yes they turn so the rotating mass is the same, but they don't have to move with up and down wheel motion (as WarpedOne said) so it is easier for the wheels to bounce up and down quickly without transmitting as much motion to the rest of the vehicle.
Personally I think they seem like a good idea, but I don't understand why they haven't been more popular. Perhaps the intrusion into cabin space is too much of a downside.
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