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On two occasions (same wheel, loosened everything off and re-did the whole thing after the first time) as I've applied a final half turn to tighten the spokes round the wheel it's gone from being pretty laterally true (within about 0.5 mm) to badly out of true (probably a couple of mm or more out).

The simplest explanation would be that I've managed to mess up by missing spokes/over under-tightening some of them, but I'm fairly sure that's not the case.

What else could cause this?

This is a rear wheel with a fair amount of dish. I'm worried that I might be over-tightening. On both occasions I decided to do a final half turn as the non drive side seemed a little loose, but I was concerned the drive side might be over tight. Could this cause a sudden change in trueness?

I've got the wheel back to a reasonable state, but I'm no longer sure I have even tension in the spokes.

  • Did the wheel go pringle-shaped with loose spokes on the side the rim has bent to? That's a sign of overtightening and can be fixed by loosening the spokes. – ojs Oct 25 '15 at 20:26
  • @ojs - First time it was pringle shaped (didn't notice any loose spokes). Second time not quite as bad. Reversing the half turn didn't seem to fix it. – henry Oct 25 '15 at 20:31
  • how is it laced? Radial lacing can cause quite sudden changes in trueness for quite small changes in spoke tension – PeteH Oct 25 '15 at 20:33
  • @PeteH 32 holes, 3 cross. – henry Oct 25 '15 at 20:36
  • a search for "true wheel" brings up a bunch of related questions with various advice on how to true wheels. Some of it's much less dismissive of the non-tensiometer approaches than I am. – Móż Oct 25 '15 at 20:54
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From the lack of detail in your question I'm going to assume you don't have a tensiometer. If you do, please tell us what tension you're actually using and what the limits for your rim are.

edit The "final half turn" is, as Andy points out in the comments, scary. That will give you an extra 100-200N of tension at a time when you should be working in selective 1/4 turns (ie, some spokes get tightened 1/4 turn, others get loosened 1/4 turn) or even smaller increments. It's also something that will stretch spokes (ie, they'll tighten beyond their elastic limit and become permanently deformed). You can't undo that, you have to replace the spoke as it's permanently weaker than it should be. And it's not necessarily the spoke you were turning when the problem became obvious that has stretched. A spoke giving like this will produce the minor taco problem you talk about.

Building wheels without the proper tools is hard, and you have to expect to make a lot of mistakes. Completely redoing an old wheel is harder because you have spokes that are bent and some may have deformed as well as dirty threads and nipples that may be partly seized in the rim. Much online advice says "it's easy" but is specific to small wobbles recently appearing in a reasonably new wheel. You're well past that now.

What you're trying to achieve is perfectly even tension on each side of a straight rim. To do that you either need to measure the tension or do extra work to make guessing the tension easier. There are various approaches and I'll make suggestions for each:

  1. nipple feel. You guess the tension based on how hard it is to twist the spoke tool/nipple. For this to work you need to have clean threads and clean, even seating of the nipples in the rim. Very unlikely to work on older rims without eyelets unless you take the wheels apart and clean the nipples before oiling them and reinstalling. You can fake this to some extent using a degreaser and penetrating oil but if you also have rim brakes cleaning up afterwards is both crucial and difficult (you'll need to use a light solvent to remove the oil). Using this method your problems above may well be caused by one or two sticky nipples that feel tight in the rim, meaning the spoke is looser than you think it is.

  2. Spoke pinging/musical method. This can actually work, but relies on the length of the spoke section you're pinging being the same for all spokes on one side, and your sense of pitch being accurate. IME I can get a 1-2% variation by stress relieving a wheel, and 5% by pushing spokes back and forth. But I have perfect pitch so I'm excessively sensitive to changes like that. I have seen someone build a wheel this way and get nice even spoke tension. It was ~10% off the tension they wanted, but it was even and the wheel worked fine for years afterwards. Using this method your problem is that you're not getting the pitch as accurate as you need. Maybe go round and push all the spokes the same way then ping again.

  3. Position is all. Don't worry about spoke tension, just get the rim straight. This can work, much as buying a lottery ticket can make you rich. It's just that unless you happen to have even tension when the wheel is straight it's going to go out of straight very quickly. By iteratively straightening and stress relieving you can eventually get a wheel that will stay straight for a while. The more you iterate the longer it will stay straight, as long as you keep refining how you define straight. People doing this often talk about needing to get wheels straight to better than 0.1mm. Using this method your problem is that you're missing half the picture, spoke tension is also important.

These days a Park Tensiometer (TM-1) costs about the same as the labour for two wheelbuilds. I suggest making a truing stand out of an old front fork and buying the tensiometer rather than buying a truing stand and not having a tensiometer, if you're looking at spending money.

This question is more encouraging about the pitch method and is worth a look.

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    My money is on the exceeding elastic limit theory. For a very dished wheel we expect the spokes to have quite different tensions on either side. Tightening the non-drive side when the drive side is already good is asking for trouble - the non-drive side spokes have much more leverage. One turn on the non-drive side is worth about 5 turns on the drive side. So the question can be paraphrased as My wheel was true with the spokes at full tension. Then I tightened the drive side by 2 turns and the wheel buckled. Why would that be? – andy256 Oct 25 '15 at 22:07
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    @henry Half a turn is double what you should be doing for a "final tighten". If the dish is about right (within 2 mm) and the drive side spokes are tight enough and the wheel is true then stop. Wheelbuilding is like training. You can overdo it. – andy256 Oct 25 '15 at 22:14
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    @andy256 I missed that bit because I'm used to wheelbuilding where I will often run round and do half a turn to go from ~900N to ~1200N once the wheel is round and more or less true, because getting hops out of a rim that's at 1200N is hard. Then I'll go to 1/4 turn or less for the final true. But half a turn on spokes that are tight tight could do all sorts of excitement. – Móż Oct 25 '15 at 22:20
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    For those of us who are tune deaf, there are plenty of smartphone apps that will listen to stuff like this (#2 method) and let you "tune" it with more precision – user2813274 Oct 26 '15 at 2:41
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    There is a nice iPhone app called "Spoke Tension Meter" or something close to that. It seems to work well (repeatability is good, and the readings are stable), but I haven't checked the results with a "real" tensiometer. – dlu Oct 26 '15 at 4:08

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