(Eli5) Why do Buses & Trucks use 2 skinny wheels put together on each side of the axle? Instead of just using one fat wheel?
In: Engineering
Because it’s easier to make it flat that way.
Anything pressurized wants to be round, but tires work best when they have a nice flat surface to meet the nice flat road. This problem gets worse as the tire gets bigger. That’s why your bike tire can basically have a circular cross section and it’s not big deal, it just squishes some as you roll on it. But if you do that with a really big tire at speed all that flexing in the sidewall generates a lot of heat and the tire fails.
A truck or bus is so heavy that you need a tire about about 2 feet wide to provide enough surface to take the weight from the axel, but a single tire 2 wide will bulge out way too much. Two skinnier tires side by side has almost as much surface but doesn’t bulge nearly as badly because you have a sidewall in the “middle” to hold everything down.
You also have the advantage that if one goes flat the whole wheel doesn’t drop.
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