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Last summer I was on tour with my Trek 520 when my rear rim cracked. I found a bike shop, and they rebuilt the wheel with a new rim.

Recently I noticed the wheel was off center relative to the frame by about 1cm. I did some basic measurements with a string to confirm the frame wasn't bent, and inserting the wheel backwards confirmed it was the wheel.

I brought it to a bike shop and they attempted to redish it. When I picked it up the guy told me the spokes had to be adjusted unusually tight, and he was only able to correct it by so much (it's still slightly off center, but hardly noticeable). He guessed the wheel may have been built incorrectly last year (i.e., left spokes on the right side and vice-versa), although I don't see how that's possible since the spokes weren't removed from the hub when it was rebuilt.

My question in all of this is: Was the bike shop guy talking BS and could the off center wheel or tight spokes cause problems?

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I assume you mean off center along the axle (sideways) not off center radially? –  mgb Mar 22 '11 at 20:11
    
This is embarrassing.. I meant to write that the wheel was off center relative to the bike frame. So basically, the tire is slightly closer to the frame on one side. We're talking perhaps 1/2 a centimeter. –  chris Mar 22 '11 at 21:04
    
Can you edit your question to include this clarification? –  Neil Fein Mar 23 '11 at 2:51
    
@Neil: Done... It too me a second to find the Edit button. –  chris Mar 23 '11 at 7:16
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3 Answers

up vote 4 down vote accepted

The bike shop that replaced your rim replaced it either incorrectly or with the incorrect part, I suspect. At least some of the 2007-2008 Trek 520 shipped with Bontrager Maverick rims, featuring an offset spoke bed. If they did in fact use the same spokes, and if they replaced it with a normal rim of appropriate ERD, the wheel will end up dished incorrectly the amount of the offset. Similarly, if they laced the rim backwards, the wheel will end up dished incorrectly double the amount of offset. The former is more likely, especially if you didn't get your wheel rebuilt by a mechanic who routinely works on Trek/Bontrager bicycles.

An off-center wheel will cause some odd handling characteristics, almost certainly not noticeable in normal riding conditions but you'll be able to tell that your wheels are not tracking in a straight line in low-traction scenarios, such as ice or wet grated roadways. The more extreme the offset, the more noticeable this will be.

Otherwise, moz is absolutely correct about the rationale behind dishing and the ramifications of running spokes in too high of tension. I'd probably ride the wheel locally until failure but I would recommend getting a properly dished and tensioned wheel built (possibly just rebuilding this wheel with the correct spokes) before going on another tour of significant distance.

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The offset rim point is important. Whether you can detect an offset wheel is an interesting question and one that I am inclined to say no to. I've seen a variety of similar faults (misaligned single speed wheels particularly) and none of them affect the handling noticably. It's when the wheel rubs on something that the rider comes into the shop. –  Мסž Mar 23 '11 at 2:54
    
The offset spoke bed is interesting and almost certainly the cause of this. My Trek 520 is a 2007 model (glad I mentioned it now) and I was feverishly trying to find a similar Bontrager rim to replace it. Unfortunately, options are limited on Sunday nights when on tour. It was replaced by a RemerX rim (Czech brand, no surprise since this happened in Prague) and I'll bet anything it doesn't have this offset spoke bed. Thanks! Knowing the cause eases my mind a lot. –  chris Mar 23 '11 at 7:10
    
@chris - Still a bit amazing that they didn't just replace the spokes! I'm surprised enough that they were able to supply a rim with a close-enough ERD, but then they missed the offset spoke bed. Seems penny-wise/pound-foolish. –  lantius Mar 23 '11 at 18:47
    
@moz: It's only noticeable in extreme situations - the human brain is actually pretty good at balancing. However, imagine riding a tricycle with a missing rear wheel - you'd need to yaw the frame to balance, and travel in a straight line would involve partial slipping of the rear wheel. I think when you start getting over a centimeter or more of misalignment it gets noticeable when the rear wheel is in a low-friction situation. I certainly could notice when riding my Pugsley with a non-offset rear wheel; that results in a mis-dishing of 17.5mm. I also had a mis-spread frame with a 20mm offset. –  lantius Mar 23 '11 at 19:08
    
@lantius - Agreed. It was a Sunday night in Prague and I was in a pinch, so I took what I could get. Either way it didn't cost much, and allowed me to finish my tour. Meanwhile I found a nearby Trek dealer who is familiar with these wheels, and will gladly help me out. Again, thank you for bringing the offset spoke bed to my attention. –  chris Mar 24 '11 at 7:53
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Short answer: probably not. It may make your brakes harder to set up but that's all.

Dishing is having shorter, tighter spokes on one side of the wheel to move the rim towards that side relative to the midpoint between the flanges (where the spokes attach on the hub). The frame and wheel are still built symmetrically for historical reasons, but dishing allows the flanges to be assymetric so you have more space to fit cogs in.

The bike shop guy is probably right if he used a spoke tensiometer (if he didn't you need to find a better bike shop). There's a limit on how tight the spokes can be, usually set by the rim but sometimes by the hub (or with aluminium spokes, the spokes). If you overtension the spokes something will give way, usually nipples start pulling through your rim.

If he has wound the spokes up as tight as he can and the dishing is still not right, you are indeed stuck. Since it seems to work like that, I say accept it and move on. Expect the wheel to be a little more fragile than before, more likely to buckle and it will fail earlier than it should. But since it should last a lifetime, that doesn't mean it won't last until the braking surface wears away.

If the new rim is the same or only slightly different from the old one it's possible they used the old spokes, but that's penny wise and pound foolish. Spokes stretch slightly and settle into position when the wheel is built for the first time, and trying to do that a second time rarely works well - spokes are more likely to break in the future. Much better to pay the $20 or so for new spokes and be done with it. The wheelbuild labour cost is so much greater than the spoke cost that it's foolish not to just buy new spokes.

One cheat that can give you a millimetre each way is to play with the spacers and locknuts on your axle. There are thin locknuts and fat locknuts, as well as a variety of spacers. With most wheels you can swap bits around to shuffle the whole thing a little bit sideways. This changes the chainline and can mean the chain hits the frame in the smallest cog, so it needs to be done cautiously. But if you are really worried about that last millimetre that should fix it.

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I believe lantius nailed the problem (the Bontrager Maverick rim offset spoke bed), but it still boils down to using the old (and wrong) spokes with the new rim. My worry is having 20kg of gear on the bike and having spokes pop due to the high tension. I may try to find a dealer who is more familiar with how these wheels are built, and just get the entire thing redone. I love this bike too much not to do it. Thanks for the reply! –  chris Mar 23 '11 at 7:14
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On a geared bicycle the rear wheel is dished to accommadate the cassette depending on the number of cogs on the cassette. This is to set the correct chain-line. The chain-line is very important for the adjustment and operation of your gears. Your wheel rim should be off center to the hub when you look at it from the rear. Hope that helps.

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I messed up with my original post. I meant to write that the wheel is off center relative to the bike frame. It's not much, but noticeable if you look. Thanks for the reply. –  chris Mar 22 '11 at 21:07
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That is not what dishing does. The chainline is set by the hub and frame and is the same whether there's a rim laced onto the hub or not. –  Мסž Mar 22 '11 at 21:41
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