[WIP] Add physics calculations for vehicles. Not actually used anywhere yet.

IMO the situation is the opposite, if there's a super coarse override you need to make the system work, it indicates a problem with the system, and if you're making compromises based on 'this wouldn't be fun if it were realistic', why bother to simulate it in such detail in the first place?
IMO getting stuck because your traction/horsepower is too low is definitely something that should happen sometimes.