Every time the idea comes up, "unsprung mass" is thrown like a pavlovian reflex. I'm curious about what they have in mind for solving the constraints. They aren't the less experienced people around.
They probably have nothing in mind. This isn't something they're planning to make so much as something that would be cool if the technology existed. The fact that in-wheel motors are put on the same level as "detecting wear and damage", "micro-channels containing 'healing chemistries'", and "supercapacitors out of carbon fiber panels that can be used to form the body of the car" gives an indication of how likely this whole affair is.
Large outrunner motors like Emrax aren't much heavier than typical cast alloy wheels. Assuming wheel-motor eliminates disc brake components (sounds scary, right?) assembly will probably be even lighter.
At least on a performance vehicle, that's still far too heavy IMO. 40ish lbs? The (cheap) wheels on my Miata are 11 lbs, without any exotic materials or crazy engineering. Almost quadrupling the unsprung mass is a hard sell performance-wise.
Which gen Miata? IIRC NA had something like 5.5x14" wheels which are tiny. But if we look at bigger production car wheels even modest 8x18" could weigh > 30lbs.
Second, (unsprung mass/sprung mass) ratio is the thing that counts, not the mass itself. So, while 40 lbs wheel is terrible for the Miata, it might be quite ok for the vehicle twice Miata's weight.
