Originally Posted by
clubman
Well, the 622 mm bead/700 size predated the 27" Dunlop size by at least 4 decades. The industry re-embraced 700c clinchers as the standard for road bikes.
I read just today that Dunlop introduced the 27x1-1/4" tire/rim size in 1935, and it was an entirely new set of dimensions not based on any other of the numerical "A, B, C, etc" versions of metric or other existing standards.
It was also stated that the 700c/622 bead seat diameter did precede this 27" standard, using fat tires of 1-5/8" and 1-3/4" to yield rolling diameters in the 28" range.
Likely this is how "700c" racing tubulars came to be referred to by tire maker Continental as 28", not that these thin tires measure anywhere close to that rolling diameter.