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 Post subject: 700c wheel diameter
PostPosted: Fri Dec 14, 2012 12:55 am 
Old School Grand Master
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Location: Fircombe.
What is the diameter of a 700c wheel including a 38mm ish tyre?
What about 650b?
Ta,


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PostPosted: Fri Dec 14, 2012 1:49 am 
National & North West AEC
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Location: Macclesfield Forest
A 700c with a 38mm tyre will measure up at 27 inches or perhaps a little under. More like ~ 680-690mm rather than the 700mm that the size would suggest.

For mountain bikes the following is true when using a normal mountain bike tyre measured from edge to edge.
Also included the actual outer rim diameter too.

"26 inch" = 26 inches - outer rim diameter = 559mm
"650b" = 27.5 inches - outer rim diamater = 584mm
"29er" = 29 inches - outer rim diameter = 622mm

29er rims are the same diameter as those used for 700c wheels, it's just the tyre sizes that make for a different diameter.
The volume and side-wall height of the tyre make up part of the wheel diameter so there is quite alot of variation.


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PostPosted: Fri Dec 14, 2012 10:35 am 
Retro Guru
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To be strictly (and admittedly boringly) accurate, those numbers are actually the bead seat diameters -- the diameter of the bit of the rim where the tyre beads sit in use -- rather than the rim outer diameter, which is a little bit bigger.

26in is the outside diameter of a 2.1in cruiser tyre as used on the original clunkers, which is where the name comes from. Most "26in" tyres in common use are nowhere near 26in in diameter -- I have some 26x2.4in ones that are over 27in :)

Similarly, 650B tyres aren't always 27.5in, which is a number chosen because it's halfway between 26 and 29 rather than having any particular bearing in reality. As Paul's numbers show, 650B isn't halfway between 26 and 29 -- put a 2.2in tyre on all three rim sizes and the 650B is closer to 26 than 29.

29in wheels are often quite close to 29in, though ;)


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PostPosted: Fri Dec 14, 2012 1:20 pm 
MacRetro rider
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Quote:
What is the diameter of a 700c wheel including a 38mm ish tyre?


As near as damit 700mm which when divided by 25.4mm (1 inch) is 27.5 inches. Fit say 44mm wide tyres and you hit near on 28 inches exactly.


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PostPosted: Fri Dec 14, 2012 6:59 pm 
Old School Grand Master
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Joined: Fri May 01, 2009 7:11 pm
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Location: Fircombe.
Thanks y'all!

It's all a lot clearer now, :? , especially the bit about 650b wheels being bigger than 700s...
:lol:


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