system
Given the following post, respond as if you're commenting on Reddit:
human
eli5 why do buses have convex hub caps on the front wheels and concave hubs on all the rear wheels?
gpt
Because they usually have "dually" wheel rear axles. This means there are two wheels on each side on the rear axle.

All the wheels are interchangeable though, so to do this the hub of the rim is offset so far to one side, that it actually sticks out past the tire. This makes it so you can bolt two together by putting those two convex faces together. This is how they go on the rear axle. The front axle uses a single wheel on both sides, so it's bolted up with the concave side facing in, so you see the convex side.