tire sizes
On 1/9/2018 3:01 AM, Emanuel Berg wrote:
What does the letter "B" denote in the French
tire size system?
E.g., this tire
56-584 27.5x2.20 650-56B
?
B= Second revision.
'700' started out at 642mm (historically measured like wagon
wheels at the very outside diameter, 700mm). As roads
improved and tires narrowed, a new smaller lighter version
of 700 at 635mm appeared so the 642mm became "700A" and the
new one "700B".
(Since everyone just made things up to suit their
need/desire, there were two 700B, both at 1995mm=635mm and
1992mm=634mm)
Progress being inscrutable and subjective, a later revision
gave us 622mm, the still current 700C. There was a short
lived 587mm 700D, smaller yet, which failed the popularity
contest (pass/fail scoring) in the 1980s.
Lest you think that we moderns are more rational or smarter
than The Ancients, please note that your example of 650B was
known as a 26" size (26 x 1-3/4) for a hundred years and
nearly died out before being rebranded as 'twenty seven and
a half' because it's in the middle of the 26" tire range and
smaller than 27 inches.
--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971
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