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I an not talking about upgrading. How do you know when to buy new wheels because the other ones have worn out? How do you tell a wheel is worn out? I can always true a wheel back to true. And nothing is dented, but the maintenance is getting a little more than it should be.

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You can usually make a rim straight, but that is only half the job. Making it round, straight, and leaving the spoke tension balanced so that it stays round and straight is the job. My guess is that's what's missing here. –  zenbike Apr 23 '12 at 3:54

3 Answers 3

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At some point the spokes become too fatigued and start snapping.

At some point, with rim brakes, the rim wears through until it's no longer stable.

At some point the bearing races in the hub become too worn.

Of these, only the third reasonably demands that the wheel be replaced -- wheels with worn spokes can be relaced, and rims can be replaced without relacing. But in some cases, especially if more than one of the above problems is looming, it may be more cost-effective to replace the wheel rather than repair it.

And, of course, there's always the case of some sort of actual damage to the wheel -- ripped spoke holes in the flange, bent flange, "taco-ed" wheel where both spokes and rim will need replacing, etc.

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I agree with your options, but not what indicates a reasonable replacement policy. it is almost always more cost effective to replace than rebuild (ignoring possible environmental considerations), since a new rim should be built with new spokes. Only in the case of a user who can build their own, or a very high end hand built wheel is it practical. –  zenbike Apr 23 '12 at 3:50
    
Well, it's quite common to replace the rim without new spokes, and it's reasonably quick and easy to do (and hence not too expensive). Granted new spokes would be better, but how much better is the question. –  Daniel R Hicks Apr 23 '12 at 11:33
    
Common, yes. It's also common to never service your bike, to lubricate the chain until it's gathered dirt and turned it in to sludge, and to buy a bike you never ride. But does that mean it is the best or even a good option? Replacing a rim and using old spokes is cutting the life of the new build by whatever mileage was on the original wheel. Which is stupid. If you're going to do a job, do it right. You list spoke fatigue as your first reason why a wheel might be damaged enough to replace. Given that, why would you risk damaged spokes in your new wheel? –  zenbike Apr 23 '12 at 13:04
    
Maybe I just relaced my old wheel, and I'm replacing a rock-dinged rim. Or maybe it's a brand-new wheel and I'm replacing a rock-dinged rim. Or maybe I'm just cheap. –  Daniel R Hicks Apr 23 '12 at 17:50
    
Cheap is not a reason to do a poor job. Nor to recommend that doing a poor job is the right way for someone who doesn't know better. As for a dinged rim, sure. But specify that difference in your answer, or stick to the conditions the OP asked about. Or again, you just confuse the issue for those who don't know enough to decide for themselves. –  zenbike Apr 24 '12 at 2:38

Most reasonably new rims come with a wear line. There should be a groove machined into the breaking surface. Once you can no longer see this, the brakes have worn down the rim too much and the rim needs replacing.

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But a rim can easily be replaced without replacing the entire wheel. –  Daniel R Hicks Apr 22 '12 at 23:47
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Depends on the wheel. I'd venture that many machine-built wheels are probably cheaper to simply replace, spokes and hub and rim. Better machine-built wheels and handmade wheels? Yeah, I'd replace just the rim on those. –  Neil Fein Apr 23 '12 at 3:18
    
@user973810 Are you referring to the streak that seems to form on every rim I have that I try to scrub away, but am never successful? If so that is really interesting. I wonder about the accuracy of these lines. To draw a comparison to another product, my razor has a blue strip to tell me when to change it, but I find that I can go well past that and still shave comfortably. Is it the same? Maybe this should be a different question. –  Chris Belsole Apr 23 '12 at 3:21
    
On some rims, especially newer models, there will be a .5mm deep groove machined in the sidewall. When the rim is new, it looks decorative. When the rim is used, it acts as a warning that break wear has removed too much metal from the rim for safety. –  zenbike Apr 23 '12 at 3:24

There are several reasons why you might need to replace a rim or a wheel.

  1. Crash or impact damage is the most common. This can range from a tacoed rim, to flat spots or flare impacts. These are usually very visible.
  2. Spoke fatigue is a mileage issue. As a wheel is ridden, the constant tension and release of stress on the spokes will fatigue the metal until it breaks. You usually see breaks of several spokes in a short period of time. More than 3 spokes in a few weeks, or spokes breaking at the j-bend for little or no apparent cause are signs of this.
  3. Brake wear is caused by the use of a rim style brake over extended periods of time. You literally wear away enough of the metal on the sidewall of the rim that it becomes too thin to support the pressure of an inflated tire. This is rare, because a rim usually perishes from damage first, but it is dangerous, and should be replaced. There are indicator marks on newer rims to tell you this is happening.
  4. There is the possibility that the rim has become fatigued, or that there is small, non-visible damage from previous repairs that prevent the rim from being trued and tensioned evenly. This is most commonly the reason a wheel is replaced. When the rim is trued straight, measure the tension on the spokes (only on the drive side if it's a rear wheel) and if the wheel is round, and straight, but you can't make the tension at least reasonably even, then it will always come out of true quickly. This makes the maintenance load too high for most riders. It is a damaged rim, but in the least visible way.
  5. And last, if there is damage to the bearing races in the hub, then the wheel will roll rough and have more resistance than it should. The hub should be replaced.

Of course, you can replace a hub, spokes, or the rim individually. If you replace the rim, you should replace the spokes. Why risk building fatigued parts into your new rim? And if you replace the hub, unless the wheel is very new, you should build with a new rim and spokes, for similar reasons. If you can do the work yourself, you will find it cost effective to build a wheel by hand, but if not, buying a replacement wheel (unless it is a high end hand built wheel) is usually more cost effective.

Given your description, I think number 4 is your issue. I'd say time to replace or rebuild the wheel.

I hope that helps.

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