Why are the front wheels on an 18 wheeler protruding while all the rear wheels on it are inverted ??
Because they are single wheel applications. The wheel is made to fit over the brake drum and keep the tire under the vehicle instead of sticking out past the fender. If you look at the back wheels on a truck, you will notice that the inside wheel(s) is mounted the same as the steering axle wheel. The inside wheel fits over the brake drum and the outside wheel is reversed so that it will fit on the truck
The wheel backspacing is offset so that the rear duals can be mounted next to each other. The second tire on the rear reduces sway and reduces the pressure on the road. The face of the wheel (where the lugnuts are) extends out past the edge of the tire. On the rear axles of a semi, one wheel is turned around opposite of the tire next to it. So the inner tire of the dual is facing the same as on the front axle. The second (outer) tire is dished inward as you normally see it, so the faces of the two wheels touch. The actual tires have a small gap between them so that they do not rub. All 10 wheels on the semi tractor are the same, just some are spun around. All wheels are interchangeable (assuming sizing is the same). So you could swap a front and rear tire around without a problem. Hope that makes sense. Next time your out and you see a parked semi or even a 1-ton pickup truck with dual wheels, take a closer look at the rear axle. Look between the rear tires and it will hopefully make more sense.
