Carbon Powertap wheelset, rubbing spokes problem

[SalsaLover]

Hello dear wheel experts

I just built me a set of Powertap hubs on a set of NOS Colnago Carbon Rims.

Hubs and Rims are 28holes, Build is made full with DT Competitions and Sapim allow internal inverted nipples. Radia Front, 2 cross rear

The set is now built and I just went for a short ride on still not glued tubulars, to let the spokes set in, so I can do a last truing before gluing the tubies.

Problem is the spokes rub on the derailer on the small chainring/largest cog combination. It only rubs when I am sitting on it and climbing a steeper hill, If I dismount and roll the wheel there is no rub.

Off course it is due to more tension and hence flex on the spokes on that particular combination. that is clear to me, however I have built many other wheels and I never experienced rub.

The wheels are not fully centered, but they are setup exactly as my set of Boras that are slightly off center ( very little though ) from the factory.

So I would like your opinions on what to do, I thought on several options

1. rebuild the rear drive side with all heads out to minimize the offset of spokes on that side.
2. tension more the wheel so they flex less ( not so fond of this one )
3. put a thin spacer on the cassette and setup the derailer a bit more outside.
4. recenter the wheel more to the NDS to give more space to the derailer.

maybe you have other ideas or some recommendations, the wheel spokes are build with "lowish" tension, but I don't really know because I don't have a tension meter, I have always built my wheels ( more than a dozen ) on feel and never had this problem before....

here some pictures of the wheels and details to help on the diagnose

thanks so much


Colnago Powertap por Salsa_Lover, en Flickr

On new Wheels por Salsa_Lover, en Flickr

Powertap Detail por Salsa_Lover, en Flickr

DSC04716.jpg por Salsa_Lover, en Flickr

DSC04717.jpg por Salsa_Lover, en Flickr

DSC04720.jpg por Salsa_Lover, en Flickr

[rijndael]

I would start by getting them properly tensioned, with a tensiometer, and dished. Get your other wheelset properly dished too.

[Calnago]

Yes, all wheels should be centered, for sure. I've never heard of building a wheel to match the errors of another wheel. So, yes, dish it properly.

Here's my thoughts on your dilemma. First, let me say that I've had a Powertap SLC+ hub (28 hole, campy freehub) laced up to a Reynolds DV46UL clincher with DT Aerolite spokes. Terrible build. The high flange combined with the deeper profile rim and the fact that the spoke holes didn't really allow for the spoke to take a natural line to the hub flange caused breaking of spokes near the nipple. I can see from your pics that the spoke line from the nipple to the flange is also being forced to take that same kind of bend. I hope you have better luck that I did with spoke breakage. I finally relaced the hub to a low profile Hed Belgium rim and that was the end of the spoke breakage problem. Since sold those wheels to a Cat 1 racer and he's ridden the crap out of them with no issues.

To your clearance problem: That is an issue... I wouldn't even ride them like that, you are begging for a derailleur catching your spokes and ripping out the derailleur hanger and possibly causing a bad crash depending on when it happens.

1) You are using DT Comps. Round 1.8mm centers. Where they cross creates a rather thick mass when compared to flat spokes. Spoke clearance is more of an issue as you've discovered.

2) The pulling spokes on the drive side are laced heads in. With the 2x pattern that you have, the final cross means that when torque is applied to the wheel, that pulling spoke will tend to force the final spoke it is crossing outward, towards the derailleur. Not good. I would relace with the pulling spokes laced heads out.

3) You say they are tensioned on the low side. This is not good on any wheel, but it will exacerbate the problem I described above (point 2). The higher the tension, the less the pulling spoke will be able to move the spoke it is crossing.

4) And make sure your limit screw on your derailleur is adjusted properly, enough to allow the chain to go to the biggest cog, but no more. Perhaps double check the alignment of the derailleur hanger as well.

I'd say that's all you can do with this setup. Adding a spacer between the cassette and the hub itself might help, but that could create problems on the other side of the cassette near the dropout.

I'd call Saris and ask them about your problem. I'd be curious what they have to say. I don't really like powertap wheels, but I can understand their appeal given the high cost of say an SRM Campy powermeter. It is nice for sure, but clearly way overpriced, especially looking at the alternatives coming onto the market these days.

Good luck,
Cal

[WMW]

1) Take a plastic hammer to you spokes right where they come out of the flange.

2) Use something softer than steel (aluminum would be fine, or wrap a steel rod with tape) and use it to pull the spokes towards each other outside the flange, and "wrap" the spokes around each other a bit at the cross.

3) Thoroughly stress relieve multiple times, set proper and even tension, and dish.

4) Adjust your derailleur limit screw so it just barely shifts onto the big cog and no farther.

5) Make sure your derailleur hanger isn't bent! Shops have a tool for this.

6) If you still have an issue, call Powertap.

7) If they don't have a fix, and there is any space between the lockring and the dropout, put a spacer behind the cassette. If there isn't space you can create some by putting a washer on the axle.

[WMW]

2) The pulling spokes on the drive side are laced heads in. With the 2x pattern that you have, the final cross means that when torque is applied to the wheel, that pulling spoke will tend to force the final spoke it is crossing outward, towards the derailleur. Not good. I would relace with the pulling spokes laced heads out.

I should have should have read your post first, since I ended up repeating most of it.

Agree on the lacing... another reason to do elbows-in for the pulling spokes is that it tends to not jam the chain as badly if you happen to derail the chain.

[SalsaLover]

thank you,

well, as many hobby builders, I thought about buying the tension meter when I was to build my first set, but though it wasn't worth to spend some $100 on a tool to only build one set.

wrong I was I have build some a dozen ( or more ) sets by now...

Anyhow the tension is lowish, So I started by tensioning it a bit more, half a turn on the spokes all around and new truing, and voilà, no more rubbing

BTW yes they are not dead centered, but the out of dish is minimal and matches my Boras and Hyperons so I don't have to move the brakes when I change wheels.

[SalsaLover]

new "official" pic now on the "right" tension


C50 with Colnago/Powertap wheels por Salsa_Lover, en Flickr

[SalsaLover]

mmm, I just read your comments Calnago, probably it would be a good idea to rebuild it with the heads on the opposite directions at the DS as you recommend ....

... but are you sure about that ? right now I have no clicking, and remember, this only happened when I am on the little chainring, biggest sprocket when and climbing a steeper gradient seated, so that means I was going at my lowest possible speed ,

I don't know if that would be a reason to redo everything, now that the wheel is "finished", I just have to glue the tubulars....

[rijndael]

but the out of dish is minimal and matches my Boras and Hyperons so I don't have to move the brakes when I change wheels.

I understood why you did it, I just think that's the wrong way to get around the issue. Fix the Boras, don't improperly dish new wheels to match.

[SalsaLover]

after closer analysis I am with Calnago on this,

unfortunately the geometry of the Hub combined with the rim depth puts the cross exactly under the derailer roller bolt.... bummer

on other combinations probably is not the case, here it is awfully close, even if with more tension I have no pinging, there is some 1mm distance ( or less ) and if I push manually with enough force it touches

I will start by rebuilding it with the heads inverted on the DS and put a little spacers on the cassette but anyway I feel this hub would work best on a rim like an Open Pro for example, probably I will get me some 28s and rebuild it like that.

[F45]

The Park TM-1 is $60 shipped....

[F45]

I should have should have read your post first, since I ended up repeating most of it.

Agree on the lacing... another reason to do elbows-in for the pulling spokes is that it tends to not jam the chain as badly if you happen to derail the chain.

What about just moving the spokes to opposite sides of each other?