Hubcaps

[markeb01]

The reason the 3 nub hubcaps work on the 4 nub wheels is because on the 3 bump wheels, all 3 bumps are the same depth. On 4 bump wheels, 2 of the bumps are standard size (like on 3 bump wheels), and the other 2 are very shallow by comparison. So overall the hubcaps only need to stretch a small bit more to mount on a 4 bump wheel.

The difference in bump sizes can even be seen in the small disc brake wheel photo above. The north and south bumps are clearly visible. The east and west bumps are much smaller.