I’ve always wondered why the front wheels of trucks have convex hubs, while the rear wheels are concave. What’s the deal?
(pic of what I mean: http://www.joeyholiday.com/Local%20Wrecker’s%20Included1.jpg)
This is done on trucks with dual rear wheels. You wan’t all the wheels to be the same so that your spare tire (s) fit everywhere, and so that you can rotate your tires to promote even wear.
The rims are made with enough offset that you can place them convex to convex )( on the rear, and the tires will have a gap between them.
The fronts are run convex side out so that the front wheel bearings are not operating in an overhang condition.
If you look closely at a truck, with the outer rear wheel removed, the inner rear wheel is in exactly the same orentation as the front.
Kevbo nailed it, this is so the same spare can fit anywhere on the truck.