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The front rim got somewhat twisted. I do not have here the rimmer or the small tools to adjust the pins. According to my friend's version, the outer tire and the inner tire are in fine condition. The twisted rim apparently resulted from riding the bike with plastic bags inside the tire about 10km due to a flat. I think the story of fine-conditioned inner/outer tires sound too good so there may be more problems with the tire. It is at least a fact that the tire rim is twisted.

Some emergency tips to adjust the rim?

  1. is it easy to do a rim with proper tools on the road?
  2. can I use 26" rim to the front wheel and 28" rim in the position of back tire?
  3. can the 28" bike use 26" tires of the proper width? The bike has outside derailleur and rim brakes.
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Can you post a picture of "somewhat twisted"? –  zenbike Jul 2 '11 at 12:52
    
" plastic bags inside the tire " ?????? –  Moab Jul 2 '11 at 15:59
    
@Moab: what is odd with that? Appropriate emergency fix to ride back to home if you happen to have very long journey, a flat and missing proper patching tools/pump. I think someone even used some natural material inside a tire. –  user652 Jul 2 '11 at 16:55
    
@hhh: What's wrong with that is that his wheel is very likely in need of replacement. Just because you can, doesn't mean you should. –  zenbike Jul 2 '11 at 18:02
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I think in an emergency it's quite reasonable to sacrifice a wheel. But afterwards you need to accept that you did sacrifice the wheel. It's time to buy a new one. If it's been ridden like that it's probably the outer surface of the rim that's damaged, and while perhaps filing down the worst of it will make it possible to get tyres on and off, it doesn't sound good. Pictures would help. –  Мסž Jul 4 '11 at 2:14

2 Answers 2

It is a professional's job to true and tension a wheel. One worth learning to do for yourself, but not one to jump into without knowledge and the proper tools. No it is not easy to do on the road, except as an emergency " get you home" fix. Very likely, a amateur attempt to fix it on the road will result in more damage.

In addition, a "somewhat twisted" rim from riding without a tube for an extended period usually indicates a problem with the metal of the rim being physically bent. In order to true a wheel, you add tension to each spoke until the rim is straight and the wheel is round under high tension. But if the wheel doesn't start straight, the spokes will not be tensioned evenly, and the job will not last for more than a few hours, or days if you are lucky. It requires skill, and quality tools, or you will make the damage worse. I would suggest in the future, walking the bike om, rather than risking this kind of permanent damage.

If you have disc brakes, you may be able to run different sized wheels in the bike for an emergency, but it will change how the bike handles, and may affect the safety of riding the bike.

If your bike has brakes that grab the rim to stop, then you must use the original size rim to replace it, because otherwise you will have no brakes.

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First verify that none of the spokes is broken. Next, if you don't have a spoke wrench, remove the tire and the "rim strip" covering the heads of the spoke nipples. Generally the nipples will have slot for a standard (though thin but with a wide blade) screwdriver.

Find a suitable screwdriver (try to find one that fits well, wide enough to fully engage both sides of the nipple, with the blade fully into the slot) and see if you can turn any of the nipples at all. (Sometimes the nipples are corroded onto the spokes so badly they won't turn.)

Next, you have to THINK about it. The spokes alternate sides, one going to the left side of the hub, the next going to the right. If the rim is bending too far to the LEFT in one spot, you want to tighten the spokes nearest to this bend that are on the RIGHT side, while loosening slightly those on the LEFT. This is, as they said in "M*A*S*H", "meatball surgery" -- you're not going to achieve a straight rim, but you want to get it straight enough that it can turn without rubbing, then leave the rest to a bike shop.

If the lip of the rim is bent (usually outward) from hitting a bump, you can straighten it to a degree using a "monkey wrench" or stout pliers -- tighten the jaws directly over the bent spot and bend inward or outward as needed. Use a bit of cloth over the outer rim surface to minimize scratches on it that will cause braking problems.

Be sure to replace the rim strip (or cover the nipple heads with some sort of tape), since un-covered nipple heads can put a hole in a tube in remarkably little time.

In a pinch, yes, you can run a smaller wheel on a bike. You will, of course, not have brakes on that wheel (and you may in fact have to loosen the brake cable all the way or some such to keep the brake pads from rubbing on the tire). Be careful braking, and don't do any long downhill runs. Also be aware that, especially if the back tire is smaller, the ground clearance of the pedals will be reduced, so you will need to be extra careful while cornering. No need to downsize both tires (and in fact it would be a bad idea due to the brake issue).

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True so far as it goes, but if a rim is visibly twisted, it's toast. –  jefferee Jul 5 '11 at 22:36
    
If the rim is simply warped (such that it wouldn't lay flat if all spokes were removed) it's quite repairable. In fact, I've rarely seen a rim that couldn't be made serviceable (though not necessarily "true") with a bit of work. –  Daniel R Hicks Jul 5 '11 at 22:42

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