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Thread: Measuring A Rim

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    Measuring A Rim

    Bought a pair of 700c/29" Velocity Dyad rims and have two questions:

    1.) What does the 29" and the 700c stand for?

    2.) Considering the size is not listed on the tie (it only says 18-622 - not sure what that stands for, tho' - if anyone has an idea, I'd love to know), how would one go about measuring the rim to insure that the it is, in fact, a 700c/29" rim?

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    622 is the ISO bead seat diameter.

    http://www.sheldonbrown.com/rim-sizing.html

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    Senior Member Retro Grouch's Avatar
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    Both 29" and 700 mm are theoretical outer diameters with the tire installed. Frankly they are not very descriptive or useful dimensions even though that's what's commonly used.

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    18mm is the width , rather narrow if you are fitting a 2" wide Knobby tire on it..

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    You need a 700c rim...

    "29er" is a marketing term invented by someone who wanted to launch a "new" product - but did not want to compete in the MTB-Hybrid / Road-Hybrid / Trials-Hybrid / Single-
    Speed Hybrid / Cyclocross market.

    It's a 700c wide tire-wise...

    It's like me taking a pet-rock, painting it "pink" and then calling it "pinkies" in my marketing campaigns in order to appear to be something other than a pet rock and something "new".

    Slowly but surely my own customers are coming around - some even laugh now when someone says: "I just found out I have a 29er! Coolios!" (While standing over a MTB-Trials-Hybrid).

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    Quote Originally Posted by Anthony2 View Post
    Bought a pair of 700c/29" Velocity Dyad rims and have two questions:

    1.) What does the 29" and the 700c stand for?

    2.) Considering the size is not listed on the tie (it only says 18-622 - not sure what that stands for, tho' - if anyone has an idea, I'd love to know), how would one go about measuring the rim to insure that the it is, in fact, a 700c/29" rim?
    29" is a marketing term (see above) and 700C (note: large "C") is an obsolete designation for a tire that fits that diameter rim. If you really felt like measuring them, either a 29" or 700C rim will be 622mm from the bottom of the bead seat of the rim- not the outside diameter.

    A 18-622 tire is 18mm wide when mounted on a "correct" rim that has a bead seat 622mm in diameter. This is a very, very narrow tire, and may be too narrow to work correctly on a Dyad rim.
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    Even more confusing is that a 28 in. tire will fit that rim.
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    Thanks for the replies, everyone.

    Quote Originally Posted by Jeff Wills View Post
    29" is a marketing term (see above) and 700C (note: large "C") is an obsolete designation for a tire that fits that diameter rim. If you really felt like measuring them, either a 29" or 700C rim will be 622mm from the bottom of the bead seat of the rim- not the outside diameter.

    A 18-622 tire is 18mm wide when mounted on a "correct" rim that has a bead seat 622mm in diameter. This is a very, very narrow tire, and may be too narrow to work correctly on a Dyad rim.
    Sorry for the confusion, Jeff - I've been calling both the tire and the rim/wheel a "tire" my entire life, so I'm trying to break that habit.

    What I meant was that I ordered the 700c/29" Velocity Dyad RIM and received the Velocity Dyad rim (not a tire) that doesn't say much on it besides "18-622" and the hole count - so it's the rim that says "18-622", not the tire. Do those numbers (700c/29 + 18-622) make sense with each other? Or does something seem off to you? Weird to me that the size isn't written on there.

    My tires, btw, are by Panaracer and are 700/32c.

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    Btw, the inside to inside measurement comes in at 23 1/4". Does that sound about right?

    Measured from point to point:


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    Quote Originally Posted by Jeff Wills View Post
    A 18-622 tire is 18mm wide when mounted on a "correct" rim that has a bead seat 622mm in diameter. This is a very, very narrow tire, and may be too narrow to work correctly on a Dyad rim.
    The 18-622 was the RIM designation, not a tire designation. So, the "18" is the interior width of the rim and this one is a bit wider than the nearly standard 13 mm wide rims used for road tires.

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    Quote Originally Posted by Anthony2 View Post
    Btw, the inside to inside measurement comes in at 23 1/4". Does that sound about right?

    Measured from point to point:

    That's not where you measure the rim diameter. You measure it across the tire's bead seats. The measurement you show will vary widely depending on the rim's depth and configuration even if they are all 622 mm across the bead seats.

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    Quote Originally Posted by HillRider View Post
    You measure it across the tire's bead seats.
    Not sure what those are. Where exactly are they located?

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    Go check that link that DaveSSS gave in the second post for how to measure and where the measurement is taken.

    To be fair on the 29'er front a lot of the wheels billed as 29'ers have wider rims to accept the wider tires used for off road riding. As a side bonus they happen to fit the wider road tires typically used for touring or heavy duty commuting that much better. I'm running a set of this style wheel with 28mm tires and it's nice to be able to easily slip the tires and rims in past the brake shoes without dealing with the amount of overhang that would occur using a 28 on a narrow "700c" rim that you would typicaly find on a racier road bike.
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    So, there are nominal size designations such as 700C, 700A, 650A, 29rrrr,27", 28", 26", etc. None of the rims or tires with these designations will have any measurement in any common unit system that matches the nominal size designation except by coincidence. It's sort of like cast iron pipe sizing -- there is nothing about any 1/2" pipe or fitting that measures 1/2", except, of course, a 1/2" length of 1/2" pipe is 1/2" long. The only standard in bicycle tire sizing is the diameter of the bead seat which, for a nominal 700C rim/tire, is 622mm. Your rim is marked 622 which identifies it as a 700C rim as opposed to a 27" rim (bsd = 630 mm) or anything else. To figure out where the bsd is measured from. take the 622 mm/700C rim and measure what the 622 mm diameter matches. Or, look here:http://www.sheldonbrown.com/gloss_ba-n.html#beadseat

    If you look at the graphic on that page you can see that you can measure the bsd pretty well by measuring the major diameter of the rim and the depth of the bead seat from that diameter and adjusting. Alternatively, just look at the rim for a marking -- almost all will have one.

    As already mentioned, the 18 indicates the inside spacing from flange to flange. Rim manufacturers are not consistent across brands as to how they designate width. Some specify the inside width and others the outside. Typically, there is about 5 mm to 6 mm difference between the two -- your 622 18 rim is probably about 23 mm to 24 mm measured from braking surface to braking surface, unless it's designed for a disc brake in which case it doesn't have a braking surface.

    By now you should see that the tires for the rim you have are standard 700C tires. Some people say that the narrowest tire you should use needs to be a little wider than the outside rim width -- in your case that would be a 25 mm tire. That would seem a little narrow on that rim to me. People put really fat tires on rims that wide. There is a table giving recommended maximum and minimum tire widths for various rim widths on the sheldon site. See here for that graphic and a bunch of other really important stuff about tire sizing:http://www.sheldonbrown.com/tire-sizing.html

    edit: I see that you have 700C 32mm tires. They will fit those rims perfectly.
    Last edited by desconhecido; 08-10-10 at 01:41 PM.

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    Thanks, BCRider.


    desconhecido: Wow, thanks so much for the thought out and detailed reply - I really appreciate it. Good to know that the rim is, in fact, a 700c/29" rim.

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