>They also did it so they'd never have to worry about the problem of wheels
>on the two driven axles slowly becoming smaller in diameter than the two
>undriven axles. Remember that the if the driven axles slipped, the undriven
>one wouldn't, so it's wheels would be slightly larger in diameter after some
>time in service.
I do not believe that the difference in diameter between the driven and
undriven wheels would be a problem in service. It must be remembered that the
40 class, together with the later 43, 44, 45 and 48 classes, had equalized
bogies.
In this type of bogie, the weight of the locomotive is distributed between the
axles by means of beams resting on the axle boxes. The weight on each axle
does not alter because of rough track or uneven wheel wear. This is not case
on 42, 421, 422, 442 and later designs, which were not equalized, and uneven
wear would cause uneven weight distribution.
John McCallum