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I just bought a new set of tires (Continental UltraRace 25-622 700x25c) for my bike, which has rims Rigida 28 x 1 5/8 x 1 1/8 - 700c.

When I inflate the inner tube (both a Schwalbe 28" 18/28-622/630 and a Bontrager 27x7/8-1, 700x18-25c, and for both sizes to pressures 2 and 4 bars) the tire doesn't inflate in a symmetric way. The final result is that the whole of the wheel is not true (i.e. a perfect circle) even though the rim is.

What could be the cause for it? The natural answer would be the difference in size between rims and tires, but the old tires (Wolber 25_622, 700 -25c) didn't have such a problem.

Thanks in advance for your help!

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    You shouldn't be inflating a tire which doesn't appear to be on properly past 1 bar - the tire could blow off the rim or you could puncture the tube.
    – Batman
    Sep 13, 2014 at 12:52

1 Answer 1

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Three posibilities:

  1. The tire is defective (least likely).
  2. The tire is simply not settling onto the rim properly.
  3. You managed to twist/pinch the tube while installing.

If you twisted/pinched the tube then there will be low spots, where the tire does not seem to inflate fully. If you suspect this, of course, remove and reinstall the tube.

If you're convinced the tube is not twisted, slowly inflate the tire while you inspect the junction between tire and rim, all around on both sides. (There is generally a rib on the tire sidewall positioned such that it will be about 1/8" from the rim edge all around when the tire is perfectly centered.) With your hands, "work" the tire one direction or the other to keep this distance equal all around as you slowly inflate.

Sometimes tires are hard to get seated properly when new (because, eg, they were hanging on a hook in the shop for months), but quickly "take a set" and are no trouble if you have to dismount/remount the tire later.

I'll add that sometimes the problem is that the thickened portion of the tube near the valve has gotten caught between the tire bead and the rim. This will prevent the tire bead from seating on the rim hook properly in the vicinity of the valve. The solution is to completely deflate the tube, then press the valve most of the way in with your finger while you manipulate the tire in the area of the tube. This should cause the "captured" part of the tube to work loose.

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  • Thanks! But do you actually exclude the possibility that the cause is the difference in the size between tires and rims? I'm going to try what you suggest, in specific the second one, that looks like the most probable for me!
    – Giovanni De Gaetano
    Sep 13, 2014 at 23:10
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    I'll exclude it. While there are good tire widths for particular (bead seat diameters)[sheldonbrown.com/tire-sizing.html#width], you're pretty far from the condition that the tire should not mount properly (mounting a 23c tire a mountain bike rim which took very fat 29er tires before, or vice versa for example). I'm willing to bet the tube didn't sit in properly. Some tire+rim combinations are finicky though!
    – Batman
    Sep 13, 2014 at 23:32
  • Tires can get worn out and bulge where the threads are most worn, which might create the appearance of an out of true rim. This is most obvious after you've inserted your dollar bill to hold in the tube.
    – T.C. Proctor
    Nov 6, 2015 at 2:28

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