The C in 700C

[zzpza]

What does it mean? Clincher? Would that make a tub wheel a 700T? 

TIA! 

[kyuss]

It's to do with an old French sizing system I believe and something to do with rim widths, where the A-D suffix represented the rim width ie 700A being narrow, 700D being wide. I guess C, being fairly close to the middle, was decided as the standard when advances in technology rendered these measurements fairly reduntant. I don't think it has anything to do with whether or not it's clincher or tub.

Sheldon Brown, as ever, has a good description of this kind of thing.

[rogerzilla]

It was a pretty big tyre, giving a nominal rolling diameter of 700mm (27.6").  A 700 x 23c tyre is about 26.4" in rolling diameter.

[zzpza]

Ah-ha! Thanks.

[andrew_s]

It's to do with an old French sizing system I believe and something to do with rim widths, where the A-D suffix represented the rim width ie 700A being narrow, 700D being wide.

It was tyre widths rather than rim widths. "A" was about 29mm, "B" was about 33mm, "C" was about 39mm, and "D" was about 56mm (?).
So a 700c rim was for a 39mm (ish) tyre that was 700mm in outside diameter, and a 650B rim was for a 33mm tyre with a 650mm outside diameter.

It wasn't that long before non-standard tyres were produced, so a 700Cx32 tyre is a 32mm tyre that fits on a rim made for a 700mm size C tyre. You have the same in imperial measure, with 27" x 1 1/4" x 1 1/8" being a 1 1/8" wide tyre that fits on a rim made for a 27", 1 1/4" wide tyre.