This thread (together with something else which is completely unrelated) got me to thinking about a weird concept. It might be good for the Automotive Weirdness thread, but I certainly have no intention of building anything along such lines, nor would I suggest that all cars, or indeed any car specifically, ought to be built along such lines. I will probably spend the next few days background-daydreaming about what could be done with the concept, and doubtless thereafter conclude that it isn't really worthwhile. The diameter of the driven tyres has a bearing on the effective torque multiplication situation: the taller the driven tyres, the more torque multiplication you need. In terms of the torque capacity of components, as we've seen, the smaller the driven tyres, the lighter the drivetrain components could be. Of course the final drive ratio would need to be adjusted taller to compensate for shorter tyres. There would be further advantages, i.e. lower drivetrain height meaning less drivetrain encroachment into the interior, lower unsprung-mass CG height, rear packaging is simpler, etc. The disadvantages would be that smaller tyres have smaller contact patches, have lesser load capacities, and don't deal quite as well with road irregularities: apart from the arrangement looking really, really weird with normal-sized front wheels. Assuming that you could design around the weirdness, much of that could be remedied by using multiple tyres on the back. For instance, six classic Mini 165/70R10s have almost 40" of section width between them, and can carry about 4700lbs, but they are barely 19" tall. The first vision I had in my head was the six tyres spaced evenly across the width of the car a bit like some old semi-trailers, e.g. the military one below; but perhaps a sort of "triply" arrangement might be more practical. One advantage of the widely-spaced wheels is that more than two brakes could be used, useful when there is barely space for a 7" drum inside a 10" wheel. With six rear wheels, the middle pair could be driven directly off the ring gear, with the outer wheels fixed in two pairs driven through a differential, via CV-jointed shafts: which might be good for traction. Each pair could be on a little axle suspended independently from the other pairs, but without any roll stiffness between the two wheels of a given pair, which would give good camber consistency regardless of where the rear roll centre is located. I'm not sure that the aesthetics could be swung, though.