If by "EV" you mean "electric car", then they almost always do (and it's almost always a single fixed reduction, around 10:1). But a lot of non-car electric ve

If by "EV" you mean "electric car", then they almost always do (and it's almost always a single fixed reduction, around 10:1). But a lot of non-car electric vehicles (maybe the majority) use hub motors, where the wheel's angular velocity is the same as the motor's. That's not the whole story, though, as a more illustrative number is the ratio between wheel radius and the motor's air gap radius, multiplied by whatever reduction gearing is used. I don't think there's a name for this concept, but you could borrow "gain ratio" from bicycles (https://sheldonbrown.com/gain.html https://sheldonbrown.com/gain.html). For a hub motor the wheel pretty much has to be bigger than the motor for ground clearance (unless you're a monorail or something), so the gain ratio is less than one (maybe 0.5 for a skateboard and 0.25 for an ebike). And practical wheel speeds tend to be a lot lower than even an inexpensive motor's top speed (not surprisingly, by about a 10:1 ratio). Bottom line is a hub motor tends to be ~10 times larger than it would need to be on a peak torque basis, so fitting more torque into a smaller package (even at the expense of top speed) is a win. On the other hand solving the peak torque issue doesn't magically solve other issues that might crop up as you downsize (e.g. heat).