Re: C-21 drawing

bonefish Wrote:
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> One issue I'd like to throw out to the forum:
> driver diameter and tolerances. Online sources and
> the folio sheet call for 38 7/8" drivers for the
> C-21s (38" for the C-25) while the original
> Baldwin spec sheet (from DeGolyer
> call for 38" diameter. That's what I'm going with
> for now. As a matter of driver maintenance, the
> tires would get turned down a bit to clean up the
> tread, right? What would the tolerance be before
> tires have to be replaced? I think that's where
> the extra 7/8" came from, or just a wrong
> measurement, not sure.

Nice start on your drawing.

Driver diameter is virtually always spec’d out by the builders to a whole number inch dimension, or at least ½ inch dimension. 38-7/8” diameter is very odd to say the least, with 38” sounding much more likely.

The driver tires on these engines could be turned down until they were 1-1/4” thick, at which time they would be replaced with new tires of full thickness. New tires were often 3” thick, though 3-1/2” was also common, as were thinner tires on small diameters. If these engines used 3” thick tires, then the wheel centers would have been 32” in diameter (a standard size), and the minimum driver diameter over the tread would have been 34-1/2”.

It is possible that the locomotive could have been fitted with replacement tires of up to 38-7/8” diameter, as long as there weren’t obstructions such as the foundation brake rigging or the valve gear in the way.

Note that turning down the tires raises the tractive effort of the locomotive. On the other hand, fitting oversize tires would lower the tractive effort below the engine’s rated T.E., lowering her tonnage rating as well.



Edited 1 time(s). Last edit at 01/11/2011 08:27PM by Kelly Anderson.