Can anyone explain why almost all common diameters of steam locomotive drivers are odd sizes? I know there are reasons for different wheel diameters, but why not have drivers 48, 54, 60, 66, 72 and 78 inches in diameter rather than the almost always odd diameters such as used by the Southern Pacific which were mostly as follows:
0-6-0s: 51 and 57 inches
2-8-0s: 57 inches
4-4-0s: 69 and 73 inches
2-6-0s: 63 inches
4-6-0s: 63 and 69 inches
4-4-2s: 81 inches
4-6-2s: 73 and 77 inches
2-8-2s: 63 inches
2-10-2s: 63 inches
Articulateds: 57 and 63 inches
4-8-2s: 73 inches
4-8-4s: 73 and 80 inches
The actual driver diameters most often appear 3 inches larger than the "even" size except for the largest sizes. I have a guess why, but I don't want a "guess" answer. Thanks.
Mark
Steel tires were heated and shrunk fit onto the driving wheels. If I recall correctly these tires were about 1-1/2 inches thick in the section that contacted the railhead which added 3 inches to the driver diameter. Subtract this 3 in. and you have an actual driving wheel diameter (less tire) of a more common even number diameter.
Mark,
I posted this over on the prototype forum......
One word.....circumference
Pi x D = circumference of a circle (or wheel).
4 chuffs to 1 rotation gives you distance moved.
i.e. 69 inches x 3.141 = 216.7 inches or about 18 feet.
Backup 8 chuffs....thats 36 - 38 feet or one 'old' boxcar length. Nice to guess when you can't see the brakeman around a curve. (Counting ties helps too).
Not sure, but something from deep within my railroading ancestry seems to know this.
Try it with the other diameters.
Just a guess & I may be wrong, but I do use sound on my steam locomotives to spot cars on a long consist on my layout both in the yard and at drop-off & pick-up points.
Happy Railroading!
Mark Wallace
Collegeville PA
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