The earliest note I have is from F.J.Camm's 'Every Cyclists Handbook' (1st edition 1936) which lists all the then British 'Standard' sizes by their rim designation against size. There is no rim designation like EA1 (26 x 1.1/4") for 27 x 1.1/4", only two entries for 'Special Lightweight' rims for the sizes 26 x 1.1/4" and 27 x 1.1/4" uniquely identified as rims with a narrower internal width at 0.65" as against 0.8" specifically for "Dunlop Road Racing (High Pressure)only" tyres.
In the text accompanying the table. it notes "The Dunlop Road Racing High Pressure tyre is mounted on a special lightweight steel rim, the tyre and rim forming one complete unit, giving speed and liveliness". To me, the inference is clear, that Dunlop developed it as a racing system. and may have introduced the 27 x 1.1/4" size in the process.
Anyone have any older references than 1936 to 27 x 1.1/4 rims / tyres ?
Bob Reid
Stonehaven
Scotland.