kyselad

All my hunting in the forums and elsewhere online has me a little confused about tension in wheelbuilding. I laced up my rim, brought it up to fairly even tension, then started working on the vertical/lateral true and dish offset. Those latter 3 are all good now, but the tension is *way* uneven around the wheel. This is obvious by the musical pitch method, but also simply by flexing the spokes and by the force required to turn the nipples.

So here's the question: won't I throw the other adjustments way off by evening out the tension? And conversely, won't I be undoing all that tension work once I return to truing and dishing? Maybe there's some magic here that I'm missing that lets me handle truing and dishing without impacting tension much, but it's just not obvious to me.

For clarity, this is a front wheel, 36 spoke, 3-leading 3-trailing pattern. I know, I should go standard pattern on my first build, but where's the uber-challenge in that? Thanks for the help.

fmw

If rims were perfect then you could have consistent tension and trueness at the same time. They aren't however so there will be some variation in tension (or trueness.) On a good quality rim the variation should be minor and not major, though. Truness is more important than the consistency of the tension.

kyselad

Good to know. So in that case, am I just testing tension to make sure it's where it ought to be on average? Or should I also be making some effort to reduce the variance in tension between spokes? (and how?) The tension seems (to me at least) to be all over the place, but it sure is nicely trued and dished.

fmw

You would need to define "all over the place." I use a Park tension meter. If I had a wheel that was tensioned to an average of 20 with 25 on the tautest spoke and 15 on the loosest, I would view that as OK and not "all over the place." If the range went from 5 to 35 I would probably expect trouble. If you use good quality rims like Mavic or DT Swiss as examples, the tension should be in the ball park all the way around the wheel.

Wil Davis

fmw makes a very good point about using a perfect rim. If the tension varies from spoke to spoke more than say 5% then it is possible to spread the load across a number of spokes so that the tension is generally more even. Obviously radial or lateral trueness might suffer, but truing and stress relief is an iterative process, and the more time you take, the better will be the result (assuming that the rim isn't damaged beyond the point of being able to be trued). That is one reason that the best hand-built wheels are expensive - it's all down to time spent tweaking and truing.

Hint 1: Invest in a tensionmeter - (Park TM-1 is inexpensive, simple to use, and works very well)

I had a go at building a 36 3-leading, 3-trailing, and it was an absolute disaster. I got it laced, and sort of tensioned, but the thing looked so butt ugly (well, I was using small flanged hubs, so that was most probably not a good idea; also I was building it with double-butted spokes, which might also have been a mistake). Anyway, it was an interesting experiment, and luckily (or should I say thanks to good planning) I ended up using the spokes in a 36 x3 pattern (spokes are the same length as those used for the 3-leading, 3-trailing pattern). I got the feeling that everything would have been perfect if the spokes had been made with zero thickness… . Has anyone else ever made a decent looking 36 3-leading, 3-trailing design? (no, not just a pretty picture generated by a CADCAM program, but a real wheel!). What gauge spokes did you use? I'll bet it was using a large-flanged hub…

Hint 2: start with a simple 36 x3 or x4

Hope this helps

- Wil

kyselad

I'm fairly confident the tension varies by >5%, so I'll set to work trying to even it out. I figure some sensible tweaking should help, e.g. by finding neighbors with vastly different tensions and adjusting them out in such a way that minimizes impacts on shape.

I know I should get a tensiometer, but this is the only wheelset I plan to build for the forseeable future. I just can't justify $50+ for a $120 wheelset (that includes the hubs, rims, and spokes, all front + rear). This is a brand new Mavic MA3. So not a top-end rim, but from what I've heard decent enough that it should build up well.

As for the 3L3T pattern, it already looks quite nice in spite of the tension problem. It hurt my eyes when I initially laced it up -- lots of sad-looking curves and contortions in the spokes. But once I brought it under moderate tension and stress-relieved it a bit, it really shaped up nicely. However, I am indeed using a high-flange hub and 15 ga straight spokes (don't worry -- I'm only 125 lbs!). With a lower flange and the resulting reduction in space between spoke holes, I imagine this pattern would be a real bear.

yes

If your interested, google peter white wheel build. He describes this problem (caused by imperfect rims), and says that he cuts out the spokes and tries again w/ new rims if it is too bad.

waterrockets 

tension consistency > beingtrue

Sheldon Brown's site has a wheelbuilding page that discussing evening the tension by plucking spokes.

An earlier poster mentioned that 15-25 is an acceptable range with the TM1 tension readings, but I've built 5 wheels in 6 months with mine, and they are all 20-21, or even a little closer...

They do have up to 0.5mm wobble in various directions, but I'll never feel that on the road, and they'll never move off it with such even tension all the way around.

Al1943

Not sure but it sounds to me as if you need to check your lacing pattern and possibly change to a conventional 3-cross.

Al

Old Hammer Boy

Here's what Park suggests:

1. Determine the average tension of the spokes on one side of the wheel. (total of all tension readings divided by the number of spokes.

2. Multiply the average tension by .8 and 1.2. These numbers represent the acceptable tension range.

Of course, you'll need a tensionometer, but perhaps you could find one someone will lend you.

cascade168

If you don't care about your rims staying true, then what you say is correct. However, the thing that makes a really good build is even tension all the way around, in addition to the wheel being true. Even tension is what makes the rims stay true over time. I have built with some pretty cheap rims and, despite the imperfections, you can get them radially trued, laterally trued, dished, and relatively tensioned very closely with patience. High quality rims tend to be easier to build with, for sure. It seems like a lot of people want to take shortcuts like using one length spoke to build a wheelset and there is a certain amount of false economy in this. I have found that by using the correct lengths I can inspect the nipples at the end of the build and the spoke ends tend to be recessed almost the exact same amount for every spoke. This is a great sanity check. You can't do this if you use spokes that are not within 1mm of what they are supposed to be. It's really easy to have a loose spoke, or two, on a rear non-drive side and the wheel be perfectly true. But, these spokes would most likely be the first to break. Good tensioning is the real key to a well built wheel - and, they tend to not break spokes at all. Any book on wheelbuilding will tell you that the reason spokes break is almost always because they were not tensioned properly in the first place. I can true any new wheel to a fine spec in less than five minutes, once it has been pre-tensioned. But, that is only the first part of the job and it's the easy part. Steps like proper stress relieving and setting bends also play a big part in a good build. Tensioning to spec and relative tensioning can take me anywhere from 30min to 2hrs (I am pretty fussy). I check all my wheels after 500 miles and almost never have to touch them.

I believe that underestimating the importance of proper tensioning is folly.

Retro Grouch 

If it was my wheel, I'd start the whole tensioning and trueing process over.

Loosen every spoke until you have just one thread showing. That will give you an equal starting place for each spoke. Then gradually build a little tension into the wheel by turning each nipple an equal number of turns. Don't be impatient. Two small tension adjustments are better than one big one.

While you are doing this, it's also important to work at getting the spoke heads seated in the hub - what many people call "destressing". I'm not sure how you do that with your goofy 3 leading and 3 trailing pattern.

After you get the tension to where you want it to be, true the wheel by making equal opposit adjustments to pairs of opposing spokes. That will true your wheel while making the least affect on the overall tension.

kyselad

Funny enough, I actually did exactly the steps above when I tried troubleshooting the tension. But by threading all the spokes to the same depth (just until the threads disappeared into the nipple), it was already very clear the tone was uneven across the spokes. However, it also became clear that a pattern was emerging. In a 3L3T wheel, there are 3 clusters of 6 spokes each per flange. The pattern in each cluster is balanced, such that each leading spoke has a corresponding and similarly laced spoke in the cluster -- essentially a mirror image. These mirror-image spoke pairs have similar tone. The tone is highest for the outermost spokes of the cluster with respect to the hub flange (innermost with respect to rim) and lowest for the innermost spokes along the hub flange.

So I emailed one builder who works with the 3L3T pattern, and he explained that the different interlacing patterns mean the spokes will have different tones at the same tension. This makes sense given the observations above. Fortunately, it seems I should still be able to use tone to some extent in checking tension. 2 "mirror-image" spokes per cluster x 6 clusters = 12 spokes that should yield similar tone at even tension. That doesn't permit direct comparison with the remaining spokes, but when the tension is off on a group of 12 spokes with respect to the remaining 24, the roundness goes off. I figured this out pretty quickly when I shot for even tone (=uneven tension!) and found 3 distinct bulges, each corresponding to the center of the spoke clusters.

I know tensiometers are great and all, but for the price and my limited wheelbuilding future, I'm going to stick with tone for now and see how it comes out. I can always hit the LBS up just to check the work, and if I still can't get it right, it would be far cheaper to have them fix the tension than to purchase yet another $50 tool.

Avalanche325

One thing about the different tones. Think of a guitar. The string is tuned to a specific tension (note). When you push your finger down on a fret, you are changing the length of the part of the string that vibrates. You are effectively making the string shorter, which vibrates faster, making a higher note.

So, if your spokes are in hard contact with each other, the part of the spoke that makes the note is from the nipple to the crossover, not the hub. You will get a higher note then what the full length of the spoke would give you. The crossover point is the same as your finger on a guitar string. If you have a complex cross pattern where the vibrating portion of the spokes are different lengths, you can only compare similar spokes, as you have already found.

Al1943

This is a very good point. If you are going to use tone you need to push the underlying spoke away from the spoke you are testing so that the tone is a function of the full length of the spoke. This will also eliminate the rattling at the spoke crossing.

Al

kyselad

Yeah, I'd seen the trick with pulling aside the the laced spokes. Unfortunately, it's just not possible with this pattern. The spokes lace under and over each other so closely that there's no hope of holding them apart.

The guitar analogy is funny: I'm a guitarist and I had the same thought once I saw the symmetry emerging in the spoke clusters. If I were a better/smarter guitarist, I would have figured this out before having to stumble on the pattern empirically.

Al1943

Yeah, it's about like trying to play a b flat with six strings and a Capo.

kyselad

I've got it! My next wheel build will use bass strings instead of spokes! A cheap tuner and a few brews later, presto. Now I just need to machine some miniature tuning keys. And if I do another 3L3T pattern, I'll have a rolling 3-tone harp. I wonder if thumb picks would fit on my toes ...

Avalanche325

With the three different notes and a pick on your fork, you can get a nice major chord. Or minor, for a little darker sound.

kyselad

There's actually a formula online here for determining the pitch. By measuring the distance from the nipple to the first spoke it crosses, seems that should tell me the pitch I need for a specific tension. Does that make good/bad sense to anyone else?