The 1 1/2 inch chain line was pretty much standard in the 1930's also, with 1 3/4 inch chain line for tandems and carrier tricycles, although there were exceptions. For 3-speed derailleur machines, the recommendation was that the 1 1/2 inch line should correspond with the middle sprocket.
Bottom bracket axles with these chain lines were still listed in the Brown Brothers catalogue at the end of the 50's.
For 5- (or 10-) speed machines, I believe that the bottom bracket shell was no wider, and that the clearance was achieved by using axles which were longer on the chainwheel side. No doubt I'll be corrected if my understanding is wrong!
Neil Foddering Weymouth, Dorset, England
>From: <greenjersey@ntlworld.com>
>To: <classicrendezvous@bikelist.org>
>Subject: [CR]One and one half inches-a crucial dimension.
>Date: Sat, 5 Aug 2006 22:54:22 +0100
>
>Just read this and in the unlikely event that it is news to anyone else I
>thought I would share it.
>Apparently on a typical early post war English sports bike with fixed gear
>the measurement from the hub and bracket centre-line to the chainwheel, and
>of course the cog, should be exactly 1 1/2 inches. That seems remarkably
>short. Were bottom bracket shells narrower in those days?
>Ray Green, Brighton, England
>
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