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Building a Powertap wheel

Old 05-25-13, 03:40 PM
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Building a Powertap wheel

OK, so my 32 hole open pro has given up the ghost, so I'm going to stick a new rim on it. I'm going to use a 50mm carbon clincher. I can get one drilled 32 hole, but it will be a special order. A 24 hole rim is their standard rear. This isn't about ditching the 8 spokes, it's about rim availability. Here's my question.

Can I build the wheel with the DS as a 3x with 16 spokes and the NDS with 8 spokes 2x? I don't think I can build the 8 spoke side 3x because it will be too much angle and the spokes will foul the hub flange. This should be a good thing in terms of evening out spoke tension side to side, but what I'm concerned about is the Powertap working accurately. The owners manual says that it should be 3x, but I know there are a bunch out there that are low spoke counts and I doubt they're all laced 3x. Does anyone have any experience or ideas?
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Old 05-25-13, 03:55 PM
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As you envision it, this will be a very complex build involving strange patterns and a multitude of spoke lengths. Most rims are drilled zigzag, so if you skip holes you'll end up out of phase with spokes going to the wrong side of the rims. You can work around that, but that causes spoke length issues. Likewise, but worse when you try to lace the left flange with fewer spokes.

Unless you're a very experienced wheelbuilder (your question implies you're not) pass on this and get a rim with the smae number of holes as your hub, and build it conventionally.

To answer the second question, the build pattern has zero impact on the torque and power function of the hub since all the torque and power is transmitted hub to rim no matter what the pattern.
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Old 05-25-13, 09:56 PM
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Good thought on the offset drilling. I've asked the seller the question. I'm not sure if it's offset or on centerline. If it's offset, then 32h, no question. I don't think lacing it 8-2x on the one side is any big deal. What bugs me is that Saris specifically states it should be 3x on both sides. What that would matter, I do not know, but apparently it does.

I have moderate experience building wheels, just not Powertaps, which is where my question comes from. If it was just a normal hub, I wouldn't be concerned.
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Old 05-25-13, 10:10 PM
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Originally Posted by Fat Boy
What bugs me is that Saris specifically states it should be 3x on both sides. What that would matter, I do not know, but apparently it does.

.
The 3x requirement has nothing to do with the power functions. Odds are it's related to concerns about local stress on the flanges. It's basically an expansion of the no radial lacing policy of many hub makers.
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Old 05-25-13, 10:29 PM
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You can build a 24 holed rim using the 32 hole hub by doing a 1x radial mix 12 on each side. Skip a hole on the hub between the 1x and do a single radial spoke between the 1x. May be worth a try.

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Old 05-26-13, 05:23 AM
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+1 FB; '3x only' means nothing when you're only using half the holes in a flange. Just have the spokes at a similar tangent and all will be well.
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Old 05-26-13, 03:13 PM
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Originally Posted by FBinNY
The 3x requirement has nothing to do with the power functions. Odds are it's related to concerns about local stress on the flanges. It's basically an expansion of the no radial lacing policy of many hub makers.
Originally Posted by Kimmo
+1 FB; '3x only' means nothing when you're only using half the holes in a flange. Just have the spokes at a similar tangent and all will be well.
Copy that. The owners manual does state that the torque is transferred through the hub to the NDS, so obviously, those will have to be in some sort of a cross pattern. The newer manual on the web says, "Must have at least a 2X lacing pattern." So I'm thinking that the 3X requirement on my older model is just a case of overkill. It does make me think that it would be nice to have the greater number of spokes on the NDS, but that seems like it would make for some pretty soft tensions on that side and a pretty big tension split side to side.
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Old 05-26-13, 08:55 PM
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I rebuilt one for a 220 pound gorilla. He broke two Open Pro rims before I built it up with a Sun 18 rim. He began breaking non-drive side nipples. Because of the dish with the hub the BDS spokes tension was low. I tensioned the drive side to 130 kilos and he hadn't managed to brake a spoke until he dropped the chain into the space between the large cog and spokes. Oh well.
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Old 05-26-13, 09:22 PM
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Originally Posted by Fat Boy
What bugs me is that Saris specifically states it should be 3x on both sides.
Not in the final manual versions.

Second generation (with carbon windows on many models, same sized flanges, and threaded non drive side cap as opposed to the first generation with one large flange, Shimano brand freehub with cup and cone drive-side bearing and cartridge non-drive side, and screws securing the cap) hubs are supposed to be laced at least 2X non drive side.

The manual is silent about drive-side treatment. Unlike a conventional hub torque is transmitted through what is normally the non drive side. People have found that radial and 1X work fine.

Last edited by Drew Eckhardt; 05-27-13 at 01:13 PM.
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Old 05-26-13, 09:46 PM
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Originally Posted by FBinNY
The 3x requirement has nothing to do with the power functions. Odds are it's related to concerns about local stress on the flanges. It's basically an expansion of the no radial lacing policy of many hub makers.
It might be to ensure that the spoke pull doesn't cause unusual stresses on the load cells and throw the calibration out.
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