Unsprung weight us an irrelevance for 90% of car users, infact a lot of performance cars ,( eg Civic Type R) have quietly gone back to beam axle on rear end, which does not have low unsprung weight..I agree the possible advantages of multiple motors but think a single motor is best in the market, since it does the job anyway with simplicity at much lower cost.
Unsprung weight should always be as low as possible as a ratio of sprung weight, since that enables the wheels to most closely follow the contours of the road surface and maintain maximum contact.
The effect of an unsprung wheel/brake/suspension mass thrown up by a road ripple is to try to throw the sprung mass of the car upwards too. The greater the unsprung mass in the ratio, the more it throws the car up which can momentarily allow the wheel to bounce slightly, reducing or losing road contact which has handling and safety implications. That upward car movement also has comfort consequences. Then the greater rebound reaction throws the weight of the vehicle downward at the unsprung wheel assembly which loses drive power as the tyre compresses more than necessary.
The best illustration of the effect of excess unsprung weight is to exaggerate it to make it clear. I'm sure you will have seen examples of Monster trucks being driven over obstructions such as cars.
Remember how as the wheels contact the car, the small truck body bounces much higher away from the wheels in a hugely exaggerated way? That's because the wheel weight is far too great for the light truck and that excess thrown weight in turn throws the truck body upwards on the springs.
In essence, the higher the unsprung weight to the sprung weight for a given spring rate, the more the vehicle bounces, with all the handling, safety and comfort disadvantages that brings.
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Go and drive a live axled MK, Caterham ( Dedion has high unsprung weight and the 160 a live axle, and these are exceptionally light cars. where , where ratio would be even worse)
Most bug American cars still use live axle, which has awful unsprung weight...
In reality 90% of drivers couldn't tell and wouldn't know difference ...