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Rim Size: Is there some "quirky math" here?

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Rim Size: Is there some "quirky math" here?

Old 06-24-12, 05:39 AM
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tsappenfield
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Rim Size: Is there some "quirky math" here?

For some time now, I have been looking on ebay for a replacement Mavic rim for my vintage road bike. I notice that some sellers have rim sizes listed at 27 inches. Is this considered a 700 cm rim, because by my conversion of English to metric (1 inch = 2.54 cm), this rim is 685.8 cm?
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Old 06-24-12, 05:51 AM
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They're not the same. I don't have the expertise to go into all of the specs on rim sizing, but suffice it to say that 700C is 4mm smaller than 27", radially. 8mm diametrically. Tires are not interchangeable. If your bike is older than mid-80s, you're probably looking for 27".
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Old 06-24-12, 06:33 AM
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tsappenfield, Quirky math? Yeah, sort of. A rim for 700C is 622 mm ISO bead seat diameter. A rim for 27" has a 630 mm ISO bead seat diameter. 700C rims are also known as 29" and 18" rims in some circles, but as far as I'm aware the 27" rims and tires are known only as 27".

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Old 06-24-12, 06:38 AM
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I just went through this same drill, and another member sent me here to get size clarification:

https://sheldonbrown.com/tire-sizing.html
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Old 06-24-12, 09:55 PM
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If you think that's bad, look up Sheldon's info on "26 inch" tires! 559, 584, 590, and 597 BSD all come to mind.
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Old 06-24-12, 11:24 PM
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Originally Posted by tsappenfield View Post
I notice that some sellers have rim sizes listed at 27 inches. Is this considered a 700 cm rim, because by my conversion of English to metric (1 inch = 2.54 cm), this rim is 685.8 cm?
TSapp
There's some quirky math there. I'm pretty sure rims almost 7 meters in diameter are a special order item.
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Old 06-25-12, 04:49 AM
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Originally Posted by Maxturbo View Post
I just went through this same drill, and another member sent me here to get size clarification:

https://sheldonbrown.com/tire-sizing.html
This should be required reading for everyone.


Tire/rim sizing should be standardized to ISO number x width.
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Old 06-25-12, 05:05 AM
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The real fun is when you have a older 26 inch chrome wheel with no clearing marking and no tire.
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Old 06-25-12, 05:08 AM
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Originally Posted by zukahn1 View Post
The real fun is when you have a older 26 inch chrome wheel with no clearing marking and no tire.
The guy at the recycling place doesn't care what size (or shape) the scrap metal is in...
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Old 06-25-12, 05:16 AM
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It's not that the math is quirky, it's that there's no math! What we have is just a combination of ancient standards and marketing chatter with modern standards and marketing chatter. Sheldon's is probably the best Rosetta stone.
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Old 06-25-12, 06:12 AM
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Originally Posted by Road Fan View Post
It's not that the math is quirky, it's that there's no math! What we have is just a combination of ancient standards and marketing chatter with modern standards and marketing chatter. Sheldon's is probably the best Rosetta stone.
Well said!!
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Old 06-25-12, 08:39 AM
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Tx!
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Old 06-25-12, 08:51 AM
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I hate when 700c wheels are called 28" or 29" because they are SMALLER than 27" rims and those are not accurate descriptions. Although the tires are not interchangeable, 27 inch tubes can work on a 700c rim and tire in the range of 25- 32 mm wide. I was uncomfortable buying them that way, but now that I've done it, it's no problem and some tubes have both sizes labled on them.

If you want to use a schrader valve- the most common 27" tube- you have to ream out the valve stem hole a bit- I use them on my motorized bikes because I find that the schrader valves actually hold air longer.

Here's a bit I wrote - an Amazon review of a 700c tire with some equivalent measurements
https://www.amazon.com/Kenda-K184-Urb...owViewpoints=1

Last edited by harpon; 06-25-12 at 08:55 AM.
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