Unsprung weight concerns
The major disadvantage of wheel hub motors are that the weight of the electric motors would increase the unsprung weight, which adversely affects handling and ride (the wheels are more sluggish in responding to road conditions, especially fast motions over bumps, and transmit the bumps to the chassis instead of absorbing them). Most conventional electric motors include ferrous material composed of laminated electrical steel. This ferrous material contributes most of the weight of electric motors. To minimize this weight several recent wheel motor designs have minimized the electrical steel content of the motor by utilizing a coreless design with Litz wire coil windings to reduce eddy current losses. This significantly reduces wheel motor weight and therefore unsprung weight.
Another method used is to replace the cast iron friction brake assembly with a wheel motor assembly of similar weight. This results in no net gain in unsprung weight and a car capable of braking up to 1G. A good example of this is the Michelin Active Wheel motor as fitted to the Heuliez Will that results in an unsprung weight of 35 kg on the front axle which compares favorably to a small car such as a Renault Clio that has 38 kg of unsprung weight on its front axle
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