How can I keep from rounding my spoke nuts?

Question

I bought my bike new about three years ago. Since then I've had issues with spokes breaking and needing to be replaced, probably around ten times. Presumably the spokes weren't up to snuff. I've always just replaced the spokes as they break without changing out the spoke nut, then re-trued the wheel. The replacement spokes have largely been fine.

I tried truing my wheel recently and found that as I tightened the spoke nuts, a high percentage of them rounded off, or in some cases flaked apart, and had to be either removed with grip pliers, or taken out after cutting the spoke. It seems the nuts are brass. I started replacing them with steel ones, and that's been better, but I'm still rounding some of them as I try to true the wheel. My spoke wrench is a Park Tool SW-7.2, which I'd think should be adequate.

What's going wrong here? Are both batches of spoke nuts bad? Is my wrench not suitable? Am I way overtightening the nuts? I haven't seen any discussion of this problem with a quick search, so evidently I'm doing something really abnormal.

Answer 1

The main thing going wrong is the wheel keeps breaking spokes and needing repeat attention.

The life cycle of a wheel with a good initial build quality and good components is spokes virtually never breaking from fatigue and the wheel needing re-truing seldom if ever.

Anything else indicates poor build quality and/or poor components. Many wheels that come with bikes suffer from some version of this.

Good build quality consists of the builder carefully setting the angles of the spokes around the spoke flanges and sometimes at the rim, tensioning them to the highest level the rim can sustain within its fatigue and structural limit, and stress-relieving the spokes to eliminate any built-in stresses that might lead to fatigue failure at the j-bend or elsewhere.

Spoke nipples cannot necessarily sustain repeat adjustments at full tension without the flats rounding off as you're experiencing. This is especially true if the tension balance is off and some are at much higher tensions than others, or if corrosion or other sources of friction are causing more force from the wrench than ideal.

The spoke wrench you have is likely not the problem per se, but sometimes one encounters spoke nipples that are a poor fit on any wrench, or any at hand.

You might consider either rebuilding the wheels, getting them rebuilt, or otherwise getting on to a higher quality set. On the course you're on, it's likely that whatever sets of spokes are breaking, they'll all break eventually.

Answer 2

Do you have access to accurate measuring tools - a caliper would be adequate.

Try measuring across the flats of your spoke-nipples, and then get an inside measurement on your driver tool. There should be almost no difference.

I've got a driver with 4 positions of different sizes, and they differ by 0.1mm from each other. If I use a too-wide hole on a nipple, it might work or it might round off if the thread's a bit jammed.

Upshot - tight threads and a slightly-sloppy fit on the nipple driver can contribute to rounding off.

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Other factors include nipples that have been tightened with the wrong size driver but haven't yet rounded visibly, but have been weakened.

Aluminium is a terrible choice for spoke nipples and really can't be adjusted much, but that's not likely your issue.

Corroded threads increase the torque needed, so spoke thread preparation can help next time. This doesn't help if the previous mechanic couldn't be bothered. Personally I use a light wipe of Copper Clay but others use Linseed Oil or generic Grease, or dedicated spoke prep concoctions.