Nipple replacement question

Question

I am a home bike mechanic and i have build a few wheels already.

I have a perfectly good wheel-set I want to replace the nipples on for aesthetic reasons - the wheel is almost brand new.

I have a wheel building stand with dial gauges, a digital tension gauge, a good spoke spanner and a nipple driver.

my question is if i want to replace the nipples, should I:

1. measure the tension of a spoke using the digital spoke tension gauge, take out the old nipple and re-tighten the new nipple to that tension and repeat for the whole wheel.
2. measure the tension on the spokes by strumming the spoke using an frequency counter on my phone, and re-tighten the new nipple to that tension, or
3. un-tension all spokes, then replace each nipple and basically rebuild the wheel to the required tension.
4. forget it, it is a waste of time and you will only f**k it up

Method 4 is no fun, methods 1 or 2 seem conceptually easier/quicker, but will method 3, provider a better wheel build?

I am interested in what experienced wheel builders say on this?

Answer 1

There is a lot to be said for 4, but 3 is best if you are going to do this. 1 is actively bad for the rim and there is nothing to be gained by 2 if you have a tensiometer.

The conventional wisdom is if you want to re-use a rim but swap spokes, nipples, or hub, the best practice is to take off the tension a little bit at a time working in passes through the wheel, much like the opposite of adding tension "layers" when building a wheel. If you take all the tension off in one spot at once, the rim becomes unevenly loaded in that area and it's possible that fatigue or distortion can occur. Rims can withstand some amount of this (it happens each time a spoke breaks, for example), but that doesn't make it good for them.

I will note that here I'm basically parroting what I learned at UBI 20 years ago. They have each class do wheel builds and they re-use everything but the spokes, and they had us do the un-building this way. I've therefore always done it that way on my own and have not actually killed or hurt a rim by sudden detensioning. However, it's easy to see how at the very least, the rim is being very contorted in a spot where it's sudden relieved of tension, and that will never be a good thing.

Do it in half turn increments. That's probably a little conservative; I've done it in full turns and it's always been fine. (How stiff the rim is, or in other words its cross-sectional area, probably makes a difference there).

You should choose a target tension for the rebuild that you think is best with the information you have available. In some cases that would mean replicating what it has now, and not in others.

Answer 2

I would replace nipples one at at time, without any tension measurements, tightening each spoke to approximately the same tension by feel, and then do as many tightening and truing rounds around the wheel as it takes to achieve the final tension and trueness.

It's in my opinion simpler to do it in this manner, rather than un-tensioning all spokes at once, then replace the nipples when the spokes are untensioned, and then re-tension to approximately the correct tension and then do the final tension and trueness adjustments.

I don't think that by measuring tension before removing a nipple and then attempting to tighten it to exactly the same tension would help at all. Tensiometers are not very accurate, so it's likely that you would need truing no matter how hard you try to achieve the same tension for every single spoke.

This of course assumes that the rim can withstand a broken spoke. Traditionally they could withstand that (there being enough material in the rim and 36 spokes at moderately high tension), but I'm not sure what rims are available for sale today.