Fast angle wheels are wheels that have an angle on them. Since the wheels are pressed onto the axle and rotate as one whole unit, the angle allows the wheel to ride up on the curve as it goes around. The idea behind it was to reduce friction. The only friction points are the ends of the axle which press up against the truck housing. Less friction - easier rolling cars. They do live up to their claim. The main issue is that they are not prototypical. These do not require any lubrication since the axle ends are the only part making contact with the truck housing.
Postwar wheels where cut with a 90 degree angle. The wheel surface is flat. The wheels are not pressed into the axle. Rather, they rotate on the axle. The reason behind this design was for curves. The wheel on the outside of the curve needs to travel farther than the wheel on the inside curve. Since each wheel is free rotating, the outer wheel can do this independently of the inner wheel. This design also requires more lubrication as you have to oil the axle on which the wheel rotates.
Current Lionel wheels on scale rolling stock use a flat surface wheel. The newer designs roll much better than postwar designs and look more prototypical. Traditional rolling stock tend to use the fast angle wheels ( I assume they are also cheaper to produce). I think the newer designs can do very well when compared to fast angle wheels.
