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Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

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Old 03-16-07, 10:20 AM   #1
pelotonracer
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How many inches across is a 700c wheel?

I was under the impression that it was 28". But in another thread (Shimano WH-R500 700c wheelset, someone said that 27" tires were "too big" to put on a 700c wheel. I'm was like, WTF, no, they're too small... BTW, 650c is 26", right? RIGHT?!?!

Someone clear this up for me?
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Old 03-16-07, 10:24 AM   #2
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Old 03-16-07, 10:26 AM   #3
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It's 622mm
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Old 03-16-07, 10:27 AM   #4
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http://sheldonbrown.com/tire-sizing.html will clear it all up for you.
a 700c*39 tire is really 700mm = 27.56"
a 700c*23 tire is 668mm = 26.3"
just to start

Last edited by vpiuva; 03-16-07 at 11:11 AM.
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Old 03-16-07, 10:28 AM   #5
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I always thought 700c meant 700mm! What? so apparently, 700=622.
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Old 03-16-07, 10:49 AM   #6
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Quote:
Originally Posted by pelotonracer
I always thought 700c meant 700mm! What? so apparently, 700=622.
The 700 originally referred to the outside diameter of the tire. Since tire diameter varies, it's not an accurate measure.

http://www.sheldonbrown.com/tire-sizing.html
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Old 03-16-07, 11:01 AM   #7
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Quote:
Originally Posted by pelotonracer
I always thought 700c meant 700mm! What? so apparently, 700=622.
622mm is the rim size, 700mm is the tire size.
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Old 03-16-07, 11:09 AM   #8
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bike tires are usually square, as in the width of the tire= height of tire or profile=100%........so you add double the width plus 622mm(which is the standard ERD of a 700c rim) to get the diameter of the wheel with tire mounted

ERD= estimated rim diameter

so for 23's that would be 46+622= 668mm = 26.3 inches

27" wheels have an ERD of 630mm usually

IIRC with mtb 26" wheels the 26" measurement is accurate with tires that are 1.75"
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Old 03-16-07, 11:26 AM   #9
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Quote:
Originally Posted by pedex
bike tires are usually square, as in the width of the tire= height of tire or profile=100%........so you add double the width plus 622mm(which is the standard ERD of a 700c rim) to get the diameter of the wheel with tire mounted
...and if you multiply by pi, you get a good starting number for your cyclometer.
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Old 03-16-07, 11:30 AM   #10
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Originally Posted by pedex
bike tires are usually square,
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Old 03-16-07, 12:08 PM   #11
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Tires are sold to fit the "bead seat" diameter on the rims. The 27 inch tire that was the "standard" for road bikes in the 1970's fits on a rim with a "bead seat" diameter designed for that tire, and the 700c tires that are standard today fit on a rim with a "bead seat" diameter designed for them. Not interchangeable.

A different question is "how many inches across is a 700c wheel, when you include the height of the tire"? Some bike designers seem to forget that different widths of tires impact the height measurement.

As measured from the ground to the top of the tire, a 700c wheel using a tire that is 28mm wide will be slightly taller than a 700c wheel using a tire that is 21mm in width.

In 2007, we have many road bikes that were designed for ultra-narrow 700c tires. If the owner tries to use 28mm or 32mm wide tires, the clearance between the tire and fork will be next to nothing, so owners are limited to ultra-narrow tires.
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Old 03-17-07, 08:58 AM   #12
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Quote:
Originally Posted by pedex
bike tires are usually square, as in the width of the tire= height of tire or profile=100%........so you add double the width plus 622mm(which is the standard ERD of a 700c rim) to get the diameter of the wheel with tire mounted

ERD= estimated rim diameter

so for 23's that would be 46+622= 668mm = 26.3 inches

27" wheels have an ERD of 630mm usually

IIRC with mtb 26" wheels the 26" measurement is accurate with tires that are 1.75"

ERD = EFFECTIVE RIM DIAMETER or spoke nipple seat to spoke nipple seat measured across (diameter) the rim to calculate spoke length.
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