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Old 05-22-10, 01:01 PM   #1
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Custom built wheel for BionX

First off, I'm gonna preface this post by saying I don't have any clue about building wheels...

I recently swapped my BionX PL350 from a folder (20") to a full-size bike (700c). I had to get a custom made wheel at my LBS, a guy who runs his own fairly large shop and does all the work himself.

Because of an unrelated issue with the auto-assist (referenced in a previous thread), I had to seek out a BionX dealer who could help me out. After finishing the work, they mentioned that they felt the wheel was unsafe to ride on. If I remember correctly, they said there was too much lateral movement like when cornering? They said to bring it back to my LBS and tell him to build it 2 cross instead of 3 cross. They also gave me an OEM wheel to show him.

So I tried to be sensitive about it and told him that they mentioned 2 cross for safety reasons and that I had a sample wheel for him to check out. He said that he didn't need to see it and that he built it for strength. The tension just needed to be adjusted.

I took it out on my first ride to work yesterday (20mi round trip). Maybe I'm just overly sensitive now, but it does seem to be a little wobbly when going over bumps at high speed. But I'm wondering if that's because my tire pressure was a little low (which it was). Or maybe that should be expected because of the weight of the wheel and the speed I'm traveling at (averaged around 15-18, topped out around 25)? And I don't think I can compare it to my folder because that was more of an unsteady ride, in general.

Higher res here:

Besides the cross pattern, I noticed the OEM wheel uses a noticeably heavier gauge of spokes. Also, on the left side of the hub the spokes are all connected on the outside of the flange; on the right side they're all connected to the inside of the flange. Hope I'm saying that correctly.

Your thoughts are appreciated!

Last edited by v6v6v6; 05-22-10 at 08:57 PM.
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Old 06-29-10, 12:09 AM   #2
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Well, in my limited exp with these systems, I can not say for sure which way of wheel building is stronger; but on the other side what I can say as a mechanical engineer with lots of exp in designing and building various constructions is this - from a pure mechanical standpoint, heavier gauge spokes are always more safe in this applicaton, since the spokes are transferring drive forces to the rims, tire, and to the road in the end. Thinner spokes then originally used on such a motor might over time fail, there's no way of telling when and even will they fail, but - I have read quite a bit about spokes failing on such hub motors, even with stock heavier gauge spokes. So to be on the safe side, yes, I would get it redone as bionx dealer suggested, since, from mechanical side, his advice is sound, although I will say that I'm no expert on cross patterns for wheelbuilding, and what effect 3-cross could have vs 2-cross. But I can say heavier gauge spokes are generally safer and more durable, concerning the fact that they transfer the drive forces from hub motor to the wheel.
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Old 06-29-10, 10:47 AM   #3
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Several of the Bionx equipped Trek bikes have had spoke failures, and that's with a 2-cross setup and heavier gauge spokes. IMHO, narrow spokes are unsafe, with a greatly increased chance of breakage. ebike wheels are a specialty area, and really should be dealt with by experienced mechanics that know what they're doing. I'd have the wheel remade with proper spokes.
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