Rim transplant: Spokes not the same note

[freeflow]

I've just done a rim transplant (rear wheel) replacing an open pro rim on a 105 hub with a new open pro rim. Not my first attempt a rim transplant or building a wheel.

The wheel is round and straight and destressed and the spoke tensions are a quarter to half a turn below that which causes the rim to pringle.

However, when I pluck the spokes there is considerable difference in tone between some of the spokes (spokes on the same side of the wheel).

Do I assume all is OK or should I tune the spokes and then try to deal with any subsequent wobbles?

[Samuel D]

“Considerable difference in tone” is difficult to judge without hearing it, but I’d tune the spokes as well as I can while accommodating the need for radial and lateral truth. For example, you may find that you can loosen a tight spoke by half a turn and tighten the adjacent ones on that side of the wheel by a quarter of a turn each, preserving the overall rim shape (or even improving it) while also improving evenness of spoke tension.

Even when I cannot see an obvious way to preserve rim shape when fixing a local tension problem, I like to balance the spoke tensions and then go back to truing. Since a wheel is a pretensioned structure, effects of loosening or tightening a spoke can be unpredictable.

[Brucey]

With skinny DB spokes especially you are possibly still too close to tacoing the wheel, i.e. the tension may be too high. If in doubt compare with 'known good' wheels (with identical spokes).

Note also that it is possible to have a wheel that is straight and have the tensions all over the place.

If you want to demonstrate this to yourself, take a good wheel and turn every nipple on one side (say the left) of the wheel half a turn, alternating directions. Chances are that the wheel will still be pretty straight but the tensions will be (obviously) all over the shop.

You can spend a long time balancing tensions, and this does result in better wheels. However it is certainly a case of diminishing returns.

NB if you build your wheels 'skew' (i.e. 'pulling spokes' inside one flange and outside the other) using an accurate nipple setting tool (and good rims, hubs and spokes), you will have an inbuilt source of tension variation; inside spokes end up a different length vs outside spokes and the result can be all the inside spokes have a different (lower) tension from all the outside spokes. If you build a wheel this way (and BTW this is how shimano recommend that you build wheels for disc brakes) then you can expect to have to spend longer on the wheel before the tensions are entirely balanced.

cheers

[freeflow]

Thanks for the discussions. Both made useful contributions that got me there in the end.

I managed to borrow a Park Tension meter. That showed that there were a number of spokes that had odd tensions, as indicated by the sounds when plucking the spokes.

Trying to get the same note (per side) in the spokes led to a very wonky wheel. I then checked the tension chart that came with the tensiometer and realised that Brucey had a good point as the driveside tensions were at the maximum indicated for a 1.8mm spoke.

On this basis I backed off all the spokes to the start of the thread and started retensioning the wheel. As I increased the tension I found three spokes that were under significantly more tension than the rest. I reduced the tension on these three spokes to give me a straight round wheel and then wound up the tension whilst monitoring the drive side tension with the tensiometer. I stopped tensioning three units before the max on the drive side spokes and it was then only a few minor tweaks to give me a true, round and centered wheel. When I measured spoke tensions, Both the drive and both sides were encompassed within a 3 unit range per side (which given the +/-1 accuracy of the meter seems OK).

So my understanding is that I initially overtensioned the wheel,and that this was not helped by the presence of three 'odd' spokes. I'll report back here if anything odd happens over the next few weeks.

Cheers

[mercalia]

Thanks for the discussions. Both made useful contributions that got me there in the end.

I managed to borrow a Park Tension meter. That showed that there were a number of spokes that had odd tensions, as indicated by the sounds when plucking the spokes.

Trying to get the same note (per side) in the spokes led to a very wonky wheel. I then checked the tension chart that came with the tensiometer and realised that Brucey had a good point as the driveside tensions were at the maximum indicated for a 1.8mm spoke.

On this basis I backed off all the spokes to the start of the thread and started retensioning the wheel. As I increased the tension I found three spokes that were under significantly more tension than the rest. I reduced the tension on these three spokes to give me a straight round wheel and then wound up the tension whilst monitoring the drive side tension with the tensiometer. I stopped tensioning three units before the max on the drive side spokes and it was then only a few minor tweaks to give me a true, round and centered wheel. When I measured spoke tensions, Both the drive and both sides were encompassed within a 3 unit range per side (which given the +/-1 accuracy of the meter seems OK).

So my understanding is that I initially overtensioned the wheel,and that this was not helped by the presence of three 'odd' spokes. I'll report back here if anything odd happens over the next few weeks.

Cheers

I was about to suggest that. Dont know about you re tension sounds. I couldnt do it by sound alone - I think that way of doing it takes lots of experience . I built my one and only pair using the Parkes tension meter. I am not sure that mine is accurate but I measured the tensions on the original wheel and also a Spa one and used that as a target. My wheels have held true now for getting on 4000 miles having received a battering from my weight and the tracks I tend to ride. I initially started by just tighening each spoke by a fixed turn until I got the dishing right and things were not loose.

[MikeDee]

I think it's impossible to have a straight wheel with no tension variations among spokes. What you want are no large tension variations (like larger than one note difference). Balance tensions by loosening a tight spoke between two lower tensioned ones by loosening the tight one and tightening the loose ones on either side.

[Brucey]

it rather depends how good your rims are and how much time you are prepared to spend on it. I used to think it was impossible but I have built a few (exceptionally straight) rims where the spokes could be made to have identical tensions and the wheels ran perfectly true.

The thing that makes the biggest difference to the length of time it takes to achieve this is how uniformly you start the build process, i.e. with a perfectly straight rim, exactly uniform length spokes, a perfectly concentrically drilled hub, and using a really accurate nipple setting tool. With all these ingredients, in a symmetric build, you can lace and set the spokes, then just wind on an exact number of extra turns, and you can have a wheel that is within 1mm of true and has quite uniform spoke tension too. It doesn't take very long to get a wheel like that to be perfect.

You can build good wheels from a worse starting point but it just takes a lot longer to do it, and if you don't have the patience you may give up and accept more tension variation in the wheel than is ideal.

cheers