Originally Posted by
3speed
... The size 27.5" is a 650b, renamed for the MTB world, called as much because it's the size between 26" and the "29er." Because, hey, why not add More names to the bike tire world so that we can all have confusing discussions to figure out which of 3 different names for 8 different tire sizes you need... Jackasses.
*Even though other companies were doing it back in the late 80s/early 90s.
You appear to be right on the 650b being the new 27.5. I got on Schwalbe USA website, they listed nine different MTB tires as 27 1/2, 650b. But the interesting thing was that several of their city or touring tires were not available in 650b. The plain Marathon was listed as being available (underlining added for emphasis) in
26 x 1.65, 650 x 42B and that was listed as 44 X 584 as it's ETRTO size designation. So, 650b when not used as a MTB tire is still one of the many 26 inch sizes but when it goes on an MTB bike, it becomes a 27 1/2 size.
But it appears different companies are not consistent, Schwalbe used 27 1/2 inch (fractional size) and Trek listed several MTB bikes as 27.5 (decimal size). So, the manufacurers have not quite got their act together ... yet.
My vintage 3 speed in the basement that I bought used in the late 1970s is a 650b. Maybe I need to knock the dust off of it, buy some knobby tires for it and get it out so everybody can lust over my latest fad bike, a 27.5 inch bike.
I can assure you that in the 1980s, buying a 650b tire in USA was a real chore. So I am really surprised that the size seems to have made a comeback.