I have a very simple mental model of a car which is applying torque around an axle -- perhaps through a gear train -- onto the wheels. Then KE gained = torque * number of wheel rotations. The car gains a unit of velocity squared for each unit of distance it travels.
I can see that this makes sense for pretty much any car I can think of -- electric motor, gasoline, etc -- which all map some force-producing element onto wheel torque.
Here's what I'm stuck on: what's the point of the geartrain, in this simple model? Why wouldn't I just have my car on the highest gear ratio all the time so it can get fast extremely quickly, since the torque is so high?
I'd ideally like to add pieces to this intuitive model until I can explain everything about cars (or any other machine that moves).