Tandem Cycling - Dyads: bulge at every spoke hole?

Oh gurus of bulletproof wheels,

We ride 48-spoke Velocity Dyads on our tandem. I noticed recently that there is a bulge in the rim around every spoke hole on each wheel. I looked at a new, unlaced Dyad, and there are no such bulges as part of manufacturing. The bulges on my rims are certainly a response to tensioned spokes pulling on the nipples.

Is this typical of Dyads? Or do I have a ticking time bomb?

I'm attaching a picture.

Thanks!
-Greg

http://home.nannynannybooboo.com/bike/dyad_bulge.jpg

The wheel appears to have been built with the spoke tension set too high. Some discoloration around the spoke holes on clear-anodized Velocity rims isn't all that unusual, but what I'm seeing exceeds the norm.

Hopefully others who have lived with Dyads (vs adjusting a few) will have some other insights. Lacking a White Knight with Dyads who says "don't sweat it" I don't believe there is much you can do at this point aside from backing the tension off about an 1/8 of a turn around the wheel and trueing "backwards", loosen high spots instead of tightening up low-spots. You'll then want to keep an eye the rim it for signs of a cracking around the spoke holes... which is truly the point at which your rim will be terminal.

FWIW: 48° wheels are, in some cases, harder to build than 40° and 36° because it is VERY easy to over-tension the spokes. Unfortunately, this lesson is often learned the hard way.

Some more snapshots for the record. Note that the neighborhood of every spoke hole looks generally the same. When you change the lighting direction and your viewing angle, different parts of the bulge feature are highlighted. In some views you see sort of a dash in the plane of the spoke. In other views you see kind of a halo around the spoke hole area.

Yeah, I'm not imagining that this is good. Hope we find that "White Knight", Mark, who can confidently say "they all do that, no worries." (I'm not holding my breath...)

-Greg

Hold your breath?! Looks like someone was over-zealous with a spoke wrench .
Next look for cracking of the rim . . . in the meantime I'd be on the lookout for a good deal on rims.

Speaking from experience, I'm afraid that's a time bomb.

I had such wheels laced with 40 spokes which looked like photo #1. I don't have a tensiometer, but I believe that tension was a bit on the low side, at least if I compare to other bikes and to the fact I needed to check truing quite often. Spokes were straight 2.0 mm spokes (14 gauge, I think).

Due partly to our potholes – avoiding them often means jumping in a 4" hole to avoid an 8" one – tension was very uneven in the spokes and I eventually pulled one spoke on the front wheel. I used the tandem for 1 or 2 weeks with 39 spokes. The rear wheel still had all its spokes, but showed more fatigue, I think. The wheels were only 2000 - 2500 km old!

I have rebuilt both wheels using the same hubs, new double-butted spokes (for the rear wheel) and Mavic A719 rims.

Have the tension checked with a tensionometer by a bike shop before you turn any spokes. If they do not exceed manufacturer's recommendations, then you may just want to eye check them regularly for signs of cracking. Rims with ferrules that extend through both levels of the extrusion help aleviate this problem.

I had such wheels laced with 40 spokes which looked like photo #1. I don't have a tensiometer, but I believe that tension was a bit on the low side, at least if I compare to other bikes and to the fact I needed to check truing quite often. Spokes were straight 2.0 mm spokes (14 gauge, I think).

Did you compare them to other wheels with the same spoke count or fewer spokes? Was the tension uniformly low or all over the map?

The reason I ask (rhethorically) is to point out that as you reduce spoke count on a bicycle wheel you must increase spoke tension and, conversely, as you increase spoke count you reduce spoke tension. Just something to keep in mind when comparing tension between wheels with different spoke counts as this is often times why 40° and 48° wheelsets end up being over-tensioned.

As for wheels going out of true, uneven tension begats uneven tension whereas even a wheel that has uniform tension but is just a little bit low will tend to stay true. If the spoke tension is way low, then yes, the wheels true will always be going out of whack as spoke nipples back-off during use.

Have the tension checked with a tensionometer by a bike shop before you turn any spokes.

That is if you can find a bike shop that: a) has a qualified wheel builder who, b) knows how to use a tensionometer, and c) has taken the time to contact Velocity to find out what the spoke tension should be on a 48° Dyad rim. This is usually easier said than done and, again, if they aren't familiar with higher spoke count wheelsets commonly found on tandems, going by "feel" or "sound" based on experience gained building 28°, 32°, and 36° single bike wheelsets will get you back to square 1: too much tension for a widely spaced, 48° symetric tandem wheel.

Well, now here's a surprise for everyone! Velocity's response:


Hello Greg,

This is definitely not normal for any of our rims. This is actually cause by
the wheel build, It looks like the spoke tension is too low. With every
rotation the nipples are pounding into the rim causing them to bulge.

We build all of our wheels at the same spoke tension. Spoke tension is
measured in Kilograms of Force (KGF). We build the front wheel between 105 -
115 KGF, and the rear between 110 - 120 KGF.

The rim looks pretty bad, I don't know if it has much life left, or how safe
it is. I would bring the wheel to a bike shop and get a second opinion. If
they can get it tensioned and trued, you might be fine for a while. If it
won't come true you might need a new rim. I which I had a better answer for
you, but let me know if you have any other questions.'

Regards,


MD
Matthew Dennis
Customer Service/Sales
Velocity USA

Well, now here's a surprise for everyone! At least for tandemgeek.;)

I would have guessed too high of tension as well. I haven't seen enough rim failures on my own builds to know what causes them -- my wheels usually eventually die of broken spokes.

Well, now here's a surprise for everyone! Velocity's response:

Six of one, half a dozen of the other.

I got the same response from Velocity when I asked them about maximum spoke tension. The email response came just a few hours after my query. They seem to be very responsive when it comes to customer questions.

I'm feeling a little uncertain about that response from Velocity- kinda have my doubts about an undertensioned wheel causing rim damage like that.

Check out this article- http://www.bikexprt.com/bicycle/tension.htm

And let us know what the pitch of the spoke is. If you are musical in the slightest, you should be able to tell if the pitch is very high or very low. Or compare it to the pitch of a known good wheel. From my reading of the article, a properly tensioned wheel will be close to a certain pitch no matter what the spoke length or crossing pattern.

Rick

Aha! I found my records of tension measurements from when I built the wheels:


Quality time with the wheels last night. Goal was to go for higher tension until spokes broke from windup, nipples jammed completely against unthreaded spoke, or nipples started rounding. I got over a full turn on both the fronts (to my pleasant surprise) and driveside rear. Fronts tensiometered at ~130kgf (+/- a couple kgf), and rear drive side spokes are in the one-hundred-teens.

So, my records indicate that I overshot Velocity's recommended tension in the front wheel (my ~130kgF to their 105-115kgF) and hit their recommended range for the drive-side rears (my "hundred-teens" to their 110-120kgF).

Curiously, both my front and rear rims show the bulging at every hole. The front was over Velocity's spec, the rear drive side within spec, and -- presumably -- the rear non-drive side below spec on this heavily-dished 140mm 9speed tandem hub.

How d'ya like that? :eek:

-Greg

How d'ya like that?

I refer you to my original reply...;)

I refer you to my original reply...;)

What, then, is the explanation for bulging on the non-driveside of the rear wheel, which was necessarily below the spec'd tension?

Or do you think that the Velocity rep does not have proper specifications for 48spoke rim tensions?

-Greg

Makes me wonder if perhaps they had a bad batch of extrusions or a poor hard-anodizing procedure, etc.

What, then, is the explanation for bulging on the non-driveside of the rear wheel, which was necessarily below the spec'd tension?

If you send me your wheels so that I can physically inspect the rims and squeeze and pluck your spokes I'll be in a better position to answer your question.

Seriously, I'm old school. You asked what I thought based on looking a 1-dimensional photo with the information you provided in your original posting. I gave you the benefit of what my experience told me when looking at the discoloration on the rim in your first picture. The additional pictures in the subsequent post were a bit more revealling. While one of the rims has less severe maring, all of the photos suggested to me that spoke tension was uniformly too high: call it instinct, a gut feel, an old man's inablity to control his hubris. Moreover, I COULD be wrong. They could be too loose, as others suggested.

As for the Velocity rep's assessment, he's obviously at the same disadvantage as all of us: we're looking at 1 dimensional photos. Frankly, I'd have to talk with the Velocity rep before drawing any conclusions about his advise, just as I'd really need to put my hands on your wheels to accurately evaluate what happened.

FWIW: Tensionometers are great, but they aren't the end-all. I own one -- a really old Wheelsmith model -- and it does a few things really well:

1. It will confirm what my ears and hands tell me about a wheel's spoke tension.
2. It comes in handy when I don't feel like plucking spokes.
3. I've always used it when I've worked on someone else's wheel(s) because, well, that's what they expected me to do.
4. It allows me to answer questions about wheel building using a tensionometer with some degree of first hand knowledge, having used one and all.

However, my hands and fingers tend to be a much more accurate gauge of spoke tension during the building process as they give me immediate feedback when tension is getting too high. A tensionometer merely confirms what I can usually deduce...

I'm confused by the Velocity response.On several points.

1> Does drilling more holes in a rim make it able to withstand more tension? Where I'm going with this is it seems to me that a 32hole Dyad would be properly built with a total of X tension. A 48 spoke Dyad would be properly built with the same total X tension. OR,is the 48 hole extrusion heavier? I bet they use the same extrusion for all drillings.

My experience building wheels indicates that in a high spoke count wheel,lighter spokes are a must.

2> I've seen lots of under tensioned wheels brought in by customers.Not one has bulged the rim.They do break spokes tho,due to the load cycling effects.Usually on the non drive side in the rear. The common fix is to use a lighter spoke that remains tensioned through the load cucles.

3>Not related,but I am starting to use spoke nipple washers on non eyeletted rims. It makes sense to me to spread the load,but things that make sense don't always work out that way. Time will tell.

[quote=dfcas;5584086]I'm confused by the Velocity response.On several points.

1> Does drilling more holes in a rim make it able to withstand more tension?

No. It's the same extrusion in the case of Velocity rims (at least it's intended to be the same extrusion -- I think they could stand to re-tool a little more frequently, given the weight variance I've seen reported in their rims.

If you send me your wheels so that I can physically inspect the rims and squeeze and pluck your spokes I'll be in a better position to answer your question.

Seriously, I'm old school. You asked what I thought based on looking a 1-dimensional photo with the information you provided in your original posting. I gave you the benefit of what my experience told me when looking at the discoloration on the rim in your first picture. The additional pictures in the subsequent post were a bit more revealling. While one of the rims has less severe maring, all of the photos suggested to me that spoke tension was uniformly too high: call it instinct, a gut feel, an old man's inablity to control his hubris. Moreover, I COULD be wrong. They could be too loose, as others suggested.

As for the Velocity rep's assessment, he's obviously at the same disadvantage as all of us: we're looking at 1 dimensional photos. Frankly, I'd have to talk with the Velocity rep before drawing any conclusions about his advise, just as I'd really need to put my hands on your wheels to accurately evaluate what happened.

FWIW: Tensionometers are great, but they aren't the end-all. I own one -- a really old Wheelsmith model -- and it does a few things really well:

1. It will confirm what my ears and hands tell me about a wheel's spoke tension.
2. It comes in handy when I don't feel like plucking spokes.
3. I've always used it when I've worked on someone else's wheel(s) because, well, that's what they expected me to do.
4. It allows me to answer questions about wheel building using a tensionometer with some degree of first hand knowledge, having used one and all.

However, my hands and fingers tend to be a much more accurate gauge of spoke tension during the building process as they give me immediate feedback when tension is getting too high. A tensionometer merely confirms what I can usually deduce...BS alarm.:rolleyes:

With all due respect to those who talk this talk, we in the bike business put up with this for way to long. When the appropriate tools, in this case a tensionometer, were finally made available, it put an end to the customer who comes in and asks if we pluck spokes and listen for consistent pitch in the pluck. I have been involved in music all my life and am by no means tone deaf and plucking spokes for tone or for tension is just too subjective unless there is a significant difference of say 5-10 kgf between spokes. With a tensionometer, we now can build wheels that have all spokes withing 1kgf of each other and do it quickly. This is a reasonable and acceptable tolerance. That is just not attainable by plucking spokes to check tension.

No BS :)

You use a transducer clip and your chromatic tuner and you can get the pitch to within a cent or two. I doubt that a tensionometer could come to anywhere near that type of accuracy.

Then of course, I doubt also that accuracy like that is really necessary. I do think that the folks that talk about checking pitch are really referring to relative rather than absolute pitch, and as a musician, I agree that the method is an excellent way to determine that all of the spokes are at or near the same relative tension, and also to find the ones that are well off from what the rest are.

Rick

BS alarm. With a tensionometer, we now can build wheels that have all spokes withing 1kgf of each other and do it quickly. This is a reasonable and acceptable tolerance. That is just not attainable by plucking spokes to check tension.

Again, with all due respect, get off your high-horse for a second and re-read what I wrote instead of extolling the virtues of the tensionometer and poo-pooing how me (most likely you) and most other older folks who've been building wheels learned the craft while also mastering the skills needed for installing and repairing sew-ups... another lost skill.

As our friend's wheels here demonstrate -- noting that I believe he is a graduate of the Piaw Na wheel building school who likely built this wheel with Jobst Brandt's book by his side along with his trusty tensionometer and conversion tables -- a tensionometer by itself will NOT keep you from screwing up a wheel if you do not have an appreciation for what spoke tension should feel like as you build a wheel. Ignoring what should be obvious signs that a wheel's spokes are getting too tight during or are still too loose after the build and relying too much on the tensionometer readings alone can and usually will get you into trouble.

As for getting wheels tensioned within 1 kgf of uniformity around a wheel, that sounds pretty cool. I've never seen a conventionally spoked wheel -- at least the variety that the average consumer would buy and use on a tandem -- that would come out perfectly true with the tension being that equal but, again, if y'all have been able to do that quickly good-on-ya.

No BS :)

You use a transducer clip and your chromatic tuner and you can get the pitch to within a cent or two. I doubt that a tensionometer could come to anywhere near that type of accuracy.

Then of course, I doubt also that accuracy like that is really necessary. I do think that the folks that talk about checking pitch are really referring to relative rather than absolute pitch, and as a musician, I agree that the method is an excellent way to determine that all of the spokes are at or near the same relative tension, and also to find the ones that are well off from what the rest are.

Rick
You would have to turn the radio off first in the shops I've worked in, so this method would never work.;)

Really, this is way to time consuming and subjective to be used by anyone other then the home mech. Now if you did use electronics to measure pitch, sure, you could get good readings, but otherwise, pffft. You better have some extensive tone recognition training to make plucking a spoke for pitch work.

And to TG, I just finished a set a wheels for my track bike built with DT 14 straight guage spokes and every spoke is within +.5kgf of 110kgf and I really didn't obssess over it much to get it that close. Building a wheel correctly is all about what you do with it when the nipples first seat against the rim when the tension is low, not what you do with it when the tension is high. But I never could have achieved this kind of balance without a tensionometer.

Building a wheel correctly is all about what you do with it when the nipples first seat against the rim when the tension is low, not what you do with it when the tension is high. But I never could have achieved this kind of balance without a tensionometer.

And while I agree with you, it has nothing to do with our friend's problem... who also used a tensionometer.

A tensionometer is like a torque wrench, using one does not -- in and of itself -- guarantee any particular result.

That was and remains my point.

I believe he is a graduate of the Piaw Na wheel building school who likely built this wheel with Jobst Brandt's book by his side...

Yes! A card-carrying graduate. :D:D:D


...along with his trusty tensionometer and conversion tables

I don't have a tensiometer, and I've not known Piaw build with a tensiometer. With more conventional rims, I believe Piaw will typically tension until the rim does its trick of starting to taco, and then backs off half a turn and retrues to finish. I believe this is Jobst's approach.

I took a similar approach to my Dyads -- "tighter is better" -- but, of course, the Dyad has a different geometry with its "V" cross-section, and is apparently much more rigid with respect to this behavior at high tensions. The limiting factor for me as I went tighter & tighter was that some nipples weren't able to stand the wrench, and were starting to round. Also, a few spokes were getting excessive wind-up. (Park wrench, excessively-lubed nipples/threads/rim.)

After building the wheels, I rode them to the LBS, let the air out of the tires, and was the first customer whose wheels were measured their freshly-calibrated tensiometer. I was interested to see what the values were, which is interesting now that I have the specs from Velocity.

I now know that, when built, I was over-spec on the front, at-spec on the drive-side rear, and (presumably, but quite reasonably) under-spec on the non-drive-side rear.

I will see if I can visit the LBS again soon to do a re-measure with their tensiometer, since I don't have one. The front has been untouched in the one year and ~3,500miles since being built -- aside from a still-ridable dent from a very unfortunate pothole. The rear ate a pannier a couple of months ago, so I put it back on the stand and tweaked it.

My best hypothesis is that with increasing tension, a Dyad will fail at the spoke holes before tacoing. However, this doesn't satisfactorily explain my non-drive-side spoke holes.

Such a crying shame that Mavic quit making 48-spokers. :(:(:(

Thanks for all of your thoughts, everyone!

-Greg

After building the wheels, I rode them to the LBS, let the air out of the tires, and was the first customer whose wheels were measured their freshly-calibrated tensiometer. I was interested to see what the values were, which is interesting now that I have the specs from Velocity.

So a tech at your LBS used the shop's tensionometer to check the tension for you and didn't suggest that you had the front wheel just a little high for a 48h wheelset using Velocity rims? Hmmmm (http://www.bikeforums.net/showpost.php?p=5576103&postcount=8).


I now know that, when built, I was over-spec on the front, at-spec on the drive-side rear, and (presumably, but quite reasonably) under-spec on the non-drive-side rear.

Which wheel is which in your photos? In other words, was that a picture of the front or rear wheel in your original posting?

Our Dyads were built with our Hadley hubs when our fir rim failed twice in 5000 miles. The builder was a bike shop owner at the time and now works for Velocity, building wheels. 25,000 miles later and the wheels are still in excellent shape. Too bad I can't say the same for my Hadley hub. The rear was overhauled by Hadley (under warranty) at 17,000 miles. A little over 8000 miles later and it needs to be done again.

Did you compare them to other wheels with the same spoke count or fewer spokes? Was the tension uniformly low or all over the map?

The reason I ask (rhethorically) is to point out that as you reduce spoke count on a bicycle wheel you must increase spoke tension and, conversely, as you increase spoke count you reduce spoke tension. Just something to keep in mind when comparing tension between wheels with different spoke counts as this is often times why 40° and 48° wheelsets end up being over-tensioned.

As for wheels going out of true, uneven tension begats uneven tension whereas even a wheel that has uniform tension but is just a little bit low will tend to stay true. If the spoke tension is way low, then yes, the wheels true will always be going out of whack as spoke nipples back-off during use.



My comparison was with other bikes that have 36-spoke wheels, whereas the tandem wheels has 40-spoke wheels. But my 2-year-old guesstimate is that tension in the 40-spoke wheels was about half of what I have in my 36-spoke wheels. Spoke tension was fairly even at the beginning, with minor fluctuations on the rear wheel to correct lateral deviations. In its last few months, however, I had to fiddle a lot with spoke tension to keep the wheel relatively round. Just before I replaced the rims, I had 3-5 mm "bumps" on both rims... and once I had dismantled the wheels and the rims were loose on the floor, they were visibly out of round. Let's say that a set of former 22-year-old Weinmann Concave looked better when I pulled them out of service after 70 000 km!

Pictures of front rim. All pictures near the valve hole. Appearance varies based on lighting direction.

*** Just to make things more interesting, note the apparent bulge at the valve hole in the third picture! ***

http://home.nannynannybooboo.com/bike/dyads/front/IMG_7235.jpg

http://home.nannynannybooboo.com/bike/dyads/front/IMG_7247.jpg

http://home.nannynannybooboo.com/bike/dyads/front/IMG_7249.jpg

http://home.nannynannybooboo.com/bike/dyads/front/IMG_7259.jpg

http://home.nannynannybooboo.com/bike/dyads/front/IMG_7258.jpg

Pictures of rear rim. All pictures near the valve hole. Appearance varies based on lighting direction. First picture from one side, second two pictures from other side.

http://home.nannynannybooboo.com/bike/dyads/rear/IMG_7226.jpg

http://home.nannynannybooboo.com/bike/dyads/rear/IMG_7229.jpg

http://home.nannynannybooboo.com/bike/dyads/rear/IMG_7230.jpg

The latest from Velocity, after seeing the picture which shows bulging at the valve hole:


Wow, that is one messed up rim. At fist I thought it may have been under
tensioned, but looking at it again, it looks like it is over tensioned. You
have 48 spokes pulling on the rim and it looks like it's buckling around the
valve hole.

We do offer wheel building here, if you plan on replacing the rim and you
want us to build it up for you, we'd be happy to do that. As long as it's
our rim we can lace it to any hub, or you can use one of our hubs.

Let me know if you have any further questions.

Regards,


MD
Matthew Dennis
Customer Service/Sales
Velocity USA

That assessment makes a lot more sense to me.

The latest from Velocity, after seeing the picture which shows bulging at the valve hole:

How about that. (http://www.bikeforums.net/showpost.php?p=5577657&postcount=10)

Before rebuilding with new rims let me suggest you give your hub's a good looking over, with emphasis on the flanges. Make sure there aren't any signs of metal fatigue at or between the spoke holes.