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Thread: tyre/wheel size

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    tyre/wheel size

    i have just bought one of these

    http://www.ebay.co.uk/itm/700c-Alloy...item45f951fb9e


    i have sent the following question to the shop,

    (QUOTE)

    hi, i have purchased 1 of these from you recently, and have just fitted a 700 x 38c tyre to it. initially the tyre appeared to be too big for the wheel, as with the bead of the tyre in the well of the wheel, there was a gap between tyre and wheel at the opposite side, so that the tyre could pass over the wheel freely. however with the tyre centralized and inflated the 'fitting line' was correct and all seems well. my only concern is that a sudden deflation could result in rim damage as the tyre could come off completely.
    is this the right size rim for the tyre ?

    (UNQUOTE)

    i am looking for independent opinions.
    Last edited by simonplatt; 08-25-11 at 01:45 PM. Reason: bad link

  2. #2
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    It's hard to tell from the picture but I think I'm seeing what looks like a tubular tire rim, not a rim for a clincher tire. That would explain the looseness. If it truly is a tubular tire rim, you're concern is warranted and you should not try to use your clincher tire on that rim.

    Do you have a camera you could use to take a picture showing the recess in the rim for the tire? That would confirm the above statements and rule out a poorly manufactured tire.

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    Quote Originally Posted by joejack951 View Post
    It's hard to tell from the picture but I think I'm seeing what looks like a tubular tire rim, not a rim for a clincher tire. That would explain the looseness. If it truly is a tubular tire rim, you're concern is warranted and you should not try to use your clincher tire on that rim.

    Do you have a camera you could use to take a picture showing the recess in the rim for the tire? That would confirm the above statements and rule out a poorly manufactured tire.
    If you read the OP it's clear that the rim cannot be for a tubular. These have a shallow curved profile and a wired-on tire would have no restriction to just blowing over the side.

    To the OP, Many rims are made wigh deeper center wells for the explicit purpose of making installation of tires easier. With the tire in the center which has a smaller diameter than the flanges you get the slack necessary for the other side to fit over the flange. Liken it to two coins stacked, then one moved over very slightly.

    As long as the tire seats properly along the flanges, using the molded lines as a guide, than it's correct, as yours appears to be from your description. Rather than worry about it, enjoy the benefit of easier mounting, and try not to snicker when you see someone trying to horse a tire onto a rim with a shallow center well.
    Last edited by FBinNY; 08-25-11 at 08:58 PM.
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    Yeah, taking a second look, the rim in the picture is obviously photoshopped. How I missed the absence of spoke holes is a little beyond me. The OP also said the "fitting line was correct", something else I ignored. I guess it's good that I'm not the only guy posting here!

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    I've had a couple of tires I could take off with my bare hands - never had one of them blow off in normal operation (knock on wood).

    I'd inflate and deflate a handful of times. If it seems like the bead sometimes doesn't want to pop into place when aired up then I might be a little concerned otherwise roll with it.
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    I've bought from that shop and I'd hold it as very unlikely that he'd sell a tubular at that price and w/o pointing it out.
    It clearly states that it is supposed to be a 700C rim. AFAIK there's no rim that's just a tad smaller than that, so an error there is unlikely. There is however a 27" (630 mm) tyre standard, which can mount somewhat half-heartedly onto a 28" AKA 622 mm AKA 700C rim. They tend to come off at first inflation though.

    There has to be a certain slop for the tire to be mounted. If you had a "perfect" fit, the only way to get the tire on/off would be to have a rim with a removable sidewall.

    And although there are standards to shoot for, manufacturers have, or give themselves, some leeway. The center cavity of the rim can differ in design, some rims/tires are looser/tighter than others. There's been a few combinations widely known to be beasts to mount. Tires blowing off seems to be rarer, but appears to happen.

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    i am not on my own pc at mo, so waiting for reply from seller, however i have thought that an extra rim tape would reduce the slack if reqd, but i would be relatively happy to ride as is at the mo. then again, bike's not finished yet so time yet to ponder.

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    Simon, as FB' noted above the slack when the tire is on the rim is not an issue as long as it centers up nicely as you inflate the tube. The only time I'd be at all concerned is if the tire's bead didn't at least snap a little as it went over the rim during the mounting and it was easily done with no strain at all.

    I've had lots of tires where I did not need to use any levers to seat the bead and had no trouble at all. Only once did I have a tire which was apparently over size where it was so floppy that the bead didn't actually snap over the last bit of the rim even in the slightest and where it would not stay seated while inflating. It was as if I was trying to make a 27" tire fit onto a 700c it was so loose a fit.

    Adding more rim tape won't cure anything either. When inflated the beads are up against the hooks on the rim flanges and not down in the middle recess.
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    When I inflate a wheel and tire that fit like that (which is common) I usually stop inflating when the tire just takes shape but is still very soft, then work around and check to see that there is no tube poking out between the rim and tire, and that the tire is roughly centred around the sidewall of the rim. If the tube is not pinched and the sidewall of the rim is pretty much lined up with the bead of the tire then there is nothing to worry about. A sudden loss of tire pressure is completely unrelated and the tire fit on the rim has little or no effect on the outcome. Keep the tire pumped up close to the pressure printed on the sidewall because underinflated tires is a major cause of flats.

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    Idle question: Which is bigger, 700c or 27" wheels? I thought 700c were bigger (diameter) but one post indicates a 27" tire is too large for a 700c wheel. Just wondering...

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    Quote Originally Posted by goagain View Post
    Idle question: Which is bigger, 700c or 27" wheels? I thought 700c were bigger (diameter) but one post indicates a 27" tire is too large for a 700c wheel. Just wondering...
    the ISO rim size tells you that 27" is bigger, 630 vs 622mm, or 4mm in radius.


    The overall size depends on the tire, add 2x the tire width to the rim diameter to get total diameter, so for example a 29er, (700c for mtn) with a 45mm tire will be bigger overall than a 27x1-1/4.
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    Quote Originally Posted by simonplatt View Post
    i am not on my own pc at mo, so waiting for reply from seller, however i have thought that an extra rim tape would reduce the slack if reqd, but i would be relatively happy to ride as is at the mo. then again, bike's not finished yet so time yet to ponder.
    No need to enlarge the diameter of the center well with a fat rim strip. The only benefit would be making tires harder to mount. Everything is cool as it is, get out and ride it.
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