I don't know if this is true, but when I was doing training in the tyre industry, one of the leaders liked to ask, which company, globally, manufactures the most tyres? obvious answers included Michelin and the like. Their answer? Lego. apparently they pump out more rubberized tyres than any other car tyre manufacturer

again, not sure if actually true, but it makes me think there a lot of wheels out there. however, Lego also makes things with doors...