# Confused about freight car wheel sizes



## philkeys (Dec 1, 2011)

I’m confused about model freight car wheel sizes. I’ve read that the vast majority of early prototype freight car wheels were 33” for both standard and narrow gauge. I assume that this is the rolling diameter or the diameter is the middle of the tread. But I don’t find model railroad wheel sets that correspond. For example Bachmann sells three wheel sets:
1:20.3 FINESCALE 32.5mm WHEEL SETS Item No. 88071
LARGE _31.0 mm _Item No. 92421
SMALL _24.5 mm _Item No. 92422
I assume that the large and small wheel sets are 1:22.5 scale.
If I calculate it right 32.5 mm at 1:20.3 corresponds to prototype 26.0”. 31.0 mm and 24.5 mm at 1:22.5 correspond to prototype 27.5” and 21.7” None are close to 33”.
What am I missing here? What is the correct wheel size for 1:20.3 scale?


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## DKRickman (Mar 25, 2008)

First off, you didn't see many 33" wheels on the narrow gauge lines, at least in the US. 26" is about right for freight cars, and many passenger cars as well. For standard gauge, the 31 mm wheels work out to 35.4" in 1:29 - reasonably close to the 36" wheels on cars over 70 tons, as well as nearly all standard gauge passenger cars for a century and a half. The smaller wheel scales pretty close to 20" in 1:20.3, which would be used on some smaller equipment. 

As for which one is correct, that depends on your prototype. Without any more information, I'd go with the 26" wheels as the most common size on 3' gauge equipment in the US.


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