Quote Originally Posted by POD View Post
There's been a lot of discussion about whether wheels are located by the spigot or by the wheel nuts, I believe the upshot is that alloy wheels are located by the spigot being a snug fit on the hub, whereas steel rims are located by the taper of the wheel nut and do not need to be a close fit in the centre hole/spigot.
The size of the rim does not affect speedo reading, it is the rolling diameter of the tyre that does that. Tyres of the same rolling diameter will simply be 1/2" taller in the sidewall in a 15" tyre vs a 16" tyre.
I always wonder about the effect on wheel bearings, stub axles and swivel pin bearings of such a big change in wheel offset. Seems to me to be a significant change in load moments from how the factory designed the front end.
The centre spigot is there for alignment and to take gross overloads if the nuts aren't tight enough.