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Several drive side spokes on a mountain bike rear were damaged the rear mech being pushed into the wheel by a rock, with one snapping completely. I've replaced the affected spokes and have managed to get the wheel (almost) perfectly true laterally.

However, I've noticed that the wheel is out of true radially -- i.e. it has high or low points of 2-3mm in a couple of places. I don't know if this was present before I replaced the spokes or not, but I'd like to improve this before putting the wheel back on the bike.

I think I need to tighten (or loosen) spokes equally on both sides at the high (or low) points to resolve this. But doing so seems to have little or no effect when making the kind of 1/4 or 1/2 turn adjustments I used to true the wheel laterally.

Am I going about this in the wrong way? Or do I need to make much bigger changes to spoke tension to affect the radial profile of the rim?

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(BTW, probably should find a term other than "radial" for the title, since "radial" makes one first think of radial spoked wheels, which is not what you have. But a better term doesn't come to mind just now.) –  Daniel R Hicks Dec 8 '11 at 20:08
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In the Sheldon Brown glossary (sheldonbrown.com/gloss_tp-z.html#true) a wheel that is out of true vertically is referred to as being "out of round". Perhaps that's a better term for describing the problem here. –  Kibbee Dec 9 '11 at 16:10

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up vote 4 down vote accepted

It's (a lot) harder to achieve in-out motion than side-to-side, and generally requires (much) more that 1/2 turn adjustments. Plus you must usually loosen spokes on either side (2-4 spokes away) of a high spot, or tighten spoken on either side of a low spot. For low spots sometimes you need to tighten ALL the spokes except those over the spot.

But at some point you need to either scrap the rim or employ a tool to bend the rim. Bending out low spots can be effectively handled with a jury-rigged tool consisting of a couple of blocks of wood with holes drilled in them and a piece of "all thread" with a couple of nuts and washers. (I've never dealt with high spots serious enough to require the opposite tool.)

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I think I was being a bit too cautious with the adjustments I was making. Having now tried tightening by whole turns (and more) at the high spots and then by lesser amounts further away I've made good progress. Thank-you! –  Andy Dec 8 '11 at 16:00
    
Yeah, it sometimes takes some muscle. (Important, BTW, to have a good nipple wrench, one that fits well, has a broad bearing surface, and thus won't (so easily) round over the nipples.) I kind of wonder at the folks who claim that all spokes should be at the same tension -- I've never seen a wheel like that -- seems like there's always a low spot in a new rim. (Though I suspect that as the wheel "works in" after truing the tensions equalize a bit.) –  Daniel R Hicks Dec 8 '11 at 20:05

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