9

My bike has a deformation in the rear wheel, almost surely not due to the rim.

At some point the tire has a "valley", causing it to bump instead of rolling smoothly. I'd like to understand if I have to replace the tire and/or the tube.

I checked the tube and it seems alright, I put it on recently and since then the wheel has become wobbly though. Both tire and tube are 700x35 mm, and they should be the right ones for the bike, since the tire is the original one.

Update: I've "played" with the tire, deflating and re-inflating several times trying to get it seated properly. Now instead of a "depression" there is a sort of sideways deformation.

Also in this case the rim looks straight but I can't get the tire to sit right. I tried to put it in place in any way I could think, what am I doing wrong?

I've found the problem

I didn't notice it before, but the tyre was worn out on the side, and the supporting structure was deforming. I solved the issue by buying a new tyre.

|improve this question|||||
  • It appears to me (assuming that the rim is round) that the tube is twisted inside the tire. Have you recently replaced the tube (or did you perhaps ride/walk the bike a significant distance on a flat tire)? The other possibility is that the tire is simply not evenly seated on the rim -- this can usually be fixed by simply deflating, "flexing" the tire to break any seal to the rim, and reinflating. – Daniel R Hicks Sep 28 '13 at 12:12
  • I've updated the question with some more information, I'm still investigating and I'll try to give more details. – clabacchio Sep 28 '13 at 13:58
  • 2
    Spin the tire slowly while you observe the part of the tire right along the rim. Likely you will see that it's not uniformly seated on the rim -- deflate it and try to reseat it correctly. Most likely your problem is near the valve where the thicker rubber around the tube's valve has made it hard to seat the tire properly. The other possibility is that the tube is undersized -- not designed for 35mm tires -- and the thicker portion near the valve is simply not expanding as much (but the effect in the photo is rather extreme for this case). – Daniel R Hicks Sep 28 '13 at 21:53
  • One other minor detail: How much air have you put in the tire? You need at least 60psi to assure that the tire is "seated". – Daniel R Hicks Sep 29 '13 at 18:43
  • 3
    One thing to try is to deflate again, then work a bit of soapy water into the joint between tire and rim all around, then re-inflate. The soap will lubricate the tire so it will (hopefully) seat better. – Daniel R Hicks Sep 30 '13 at 0:11
8

It's hard to tell from that video - a side view would have been more useful.

From what you say it seems the rim is actually round in both planes - it doesn't wobble side to side or up and down as it rotates, so it's not that (but I can't see the rim in the video so I don't know for sure).

If the problem is the tyre it will be either because the tyre is not seated properly, or it's defective/worn out. But that sort of dip is unusual for a worn out tyre - normally they bulge (then pop). If the tyre isn't seated properly you'll normally be able to see it when you look at the side of the tyre. Where the dip is the normal markings on the side of the tyre will dip in too, meaning the bead has been pulled in on the rim rather than being pushed out against the sidewall/braking surface. If you're lucky that will have happened because the tyre wasn't installed properly. This is probably only on one side of the wheel, so check both sides. If it's on both sides probably the tyre is the wrong size for the rim, or you may just be particularly unlucky and have a slightly oversize rim and a slightly undersize tyre.

To fix, mostly deflate the tube, then work round pushing the bead in on the rim as though you were about to remove the tyre. Then pump the tyre back up slowly until the bead pops back against the rim. When this happens stop pumping, and make sure the bead has popped back all the way round. if not, work the tyre with your fingers where it hasn't popped - just squeeze the tyre in with your fingers. The movement should be enough to seat the bead properly.

But if it's a size problem you will need to buy a new tyre. If the size should be right but isn't, try a different brand of tyre. Some manufacturers are known to make "tight" tyres (slightly undersize beads), others do the opposite. Be aware that it is sometimes possible to put a 700c tyre on a 27" wheel (700c = ISO 622, 27" = 630 or so. ISO is roughly diameter, so the difference in circumference is 25mm or about an inch). It's very, very difficult to do, and shouldn't be done at all. If you're unlucky, you have one of the weird size wheels that's almost a modern size. Sheldon Brown discusses wheel sizes here

If the problem is the tube it'll be slightly harder to detect. Tubes are not every strong compared to the tyre, but if you somehow tie a knot in the tube that will affect the shape of the tyre. The most common problems here are a twist, which basically turns the tube into one of those balloon animals; and getting folded back on itself. The fold usually happens when the bike is ridden with the tyre very under-inflated or flat. The whole tyre rotates slighting on the rim as you brake or pedal, but the value stops the tube rotating with it. Until it breaks off, anyway. So you get a stretched part of the tube, and the other side of the value all the slack collects and folds up. When you re-inflate the tyre there's wobble like in your video.

I describe that first because it's easy to check and fix. Deflate the tyre, pop it off, and if there's a big lump of folded up tube next to the valve, there's your problem. Often you can tell just by deflating the tyre than pressing down around the valve.

|improve this answer|||||
  • Thank you very much for the answer. I also suppose it isn't seated properly, but I'm trying to move it and deflate it, re-inflate it and can't get it stable and right. But now (see update) the bump is gone and the tire is instead wobbly sideways. Do you think that I just have to keep trying? – clabacchio Sep 29 '13 at 21:43
  • I fear that now it's nearly seated, but now the problem is only on one side. I suspect Daniel R Hicks is right, and the problem may be at the value. One tip is to push the valve up into the tyre just before you start pumping, to make sure there's no tube under the bead at that point. If you look at a tube there's a thicker pad of rubber around the value, and if that gets under the bead that can cause problems like yours. – Móż Sep 29 '13 at 22:52
  • the bent is almost on the opposite side of the valve, do you think it may still be the case? – clabacchio Sep 30 '13 at 6:20
  • 1
    In that case, no. It's something else. – Móż Sep 30 '13 at 6:40
5

Had exactly the same problem in a 700 x 350 Duro tyre after repairing a puncture and could not understand why the back wheel wobbled so much.

Adjusted the spokes for centering the wheel, checked that there was no tube twist, all to no avail.

There was however on close inspection about a ten inch point where the Tyre looked as though it was "blown" out just a little and I though that maybe over inflation could have been the cause but I never exceeded 60 lbs so I concluded that wasn't the answer.

The answer was that the tyre as explained above had not seated properly and so I deflated the tyre again, checked for twisted tube but this time on assembling the wheel doused the tyre beads with plenty of soapy liquid.

Then I pinched the tyre all of the way round and made sure that all was correct before I re-inflated the tyre.

There was still a small area where the tyre had not seated completely down but not as much as before.

I did a test ride on a really smooth road surface and there was no discernible wobble.

Thanks to all those who posted on here and resolved my problem without going to the bike shop and spending more money and also another benefit I have learned something that may help in the future

|improve this answer|||||

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for?Browse other questions tagged or ask your own question.