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half radial lacing on XTR rear hub

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half radial lacing on XTR rear hub

Old 07-05-06, 07:57 AM
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gernot
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half radial lacing on XTR rear hub

Hi,

I am planning to build up a rear wheel for cyclocross using a 28 spoke xtr hub and open pro rim. I weigh 175 lbs. I was going to use half radial lacing, since Sheldon Brown's theory on why this is smart makes sense to me (http://sheldonbrown.com/wheelbuild.html#half-radial). Then I remembered Shimano's warranty which is voided by radial lacing. Now I am not sure which way to go. Will they not honor the warranty even for completely unrelated problems, like the freehub mechanism breaking, when a hub was built with half radial lacing? Anyone have experience with that?

I would think that radially laced left spokes are under less tension than 2 or 3 cross right side spokes on a dished wheel, so Shimano's concern about hub flange breakage with radial lacing should not be an issue with half radial. But would they use that as a reason to void the warranty anyway?

Thanks,

Gernot
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Old 07-05-06, 09:24 AM
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Originally Posted by gernot
I would think that radially laced left spokes are under less tension than 2 or 3 cross right side spokes on a dished wheel, so Shimano's concern about hub flange breakage with radial lacing should not be an issue with half radial. But would they use that as a reason to void the warranty anyway?
Spokes with higher tension do less damage to hubs than spokes with lower tension. The lower tension spokes flex more. The thing about radial lacing is that stresses are carried directly toward and away from the hub whereas with tangential crossed lacing stresses are relieved on an angle and shared through the crossings. This is explained well in the Jobst Brandt book "The Bicycle Wheel".

I've always wondered if a 1-cross pattern could be the compromise that would preserve the warranty.

Al
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Old 07-05-06, 10:23 AM
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If it's radially laced and the freehub breaks, just remove the freehub from the hub and get THAT part replaced. If the hub cracks on the radially laced side, I think you'll just have to replace the hub yourself since that would voide the warranty. Or you could get yourself a hub that will not be voided by radial lacing; I'm not sure off hand who, if anyone, makes 'em for rear wheels. Many front wheels come fully radially laced.
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Old 07-05-06, 12:59 PM
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Shimano's hub warranty is a joke anyways. I wouldn't count on them replacing any hub part under warranty.

That said, go for the half-radial lacing if the only thing holding you back is the warranty issue.
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Old 07-05-06, 11:21 PM
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Originally Posted by gernot
I would think that radially laced left spokes are under less tension than 2 or 3 cross right side spokes on a dished wheel ....
Spokes that are undertensioned tend to be the ones that break first. One of the prime objectives in building a good wheel is to get all the spokes at the maximum tension you can, given the limitations of the components (rims, spokes, hubs). For example, Mavic quotes the max tension for their rims at 90-110kgF. The rim is normally going to be the limiting factor. So, the closer you can get to 110, the better. This is what the front wheel spokes and the rear drive side spokes should be targeted to. The non-drive side spokes will be some fraction less tension than the drive side. This will be in the 70%, or so, range. It will differ from wheel to wheel, depending on a lot of things, including lacing patterns. Any non-drive side spokes are always going to be under less tension than the drive side spokes, no matter what the lacing pattern. If you want higher non-drive side tensions, then you should look at assymetric rims like the Velocity Aerohead OC ("Off Center"). Those non-drive side spokes will still be less tension than the drive side spokes, but they will be closer than a rim with a centered spoke pattern.

You say that this wheel is being used for a cross bike. I would never suggest radial spoking for off road - an element that cyclocross contains by definition. I'm not going to say they don't exist, but I have never seen a rear MTB wheel with radial lacing. I have seen front MTB wheels laced radially.
Take some time and look at MTB wheel sets and see if you can find one that has rear radial lacing. For off road, 3x is the way to go for a strong, reliable wheel. Radial patterns are for the roadies and if you watch the Paris-Roubaix race you will see that a lot of the road pros will switch from their boutique radially laced wheels and go to traditional 3x patterns to cope with the beating that the cobbles put on them. There are even some that do tying and soldering for that race, but that's another debate ......
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Old 07-06-06, 01:02 AM
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I've seen non-drive spokes break before, which makes me think that they still carry some of the torque (think about it, the gears are turning the hub, which turn both sides of spokes). For that reason, I cross both sides of my rear wheel. It may be far on the safe side, but it's only about 20 grams difference anyway.
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Old 07-06-06, 03:51 AM
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Originally Posted by gernot
i would think that radially laced left spokes are under less tension than 2 or 3 cross right side spokes on a dished wheel, so Shimano's concern about hub flange breakage with radial lacing should not be an issue with half radial. But would they use that as a reason to void the warranty anyway?
Tension and load are not the same? Tension is just a matter of turning the nipples a certain number of turns. So radial & crossed wheels are typically tensioned at the optimum amount for the rim, 100-120kgf. And load ends up being the same if you've got the same weight on the bike. A 400lb gorilla would load up each spoke in a 32h wheel exactly the same, regardless of lacing pattern.

Originally Posted by urbanknight
I've seen non-drive spokes break before, which makes me think that they still carry some of the torque (think about it, the gears are turning the hub, which turn both sides of spokes). For that reason, I cross both sides of my rear wheel. It may be far on the safe side, but it's only about 20 grams difference anyway.
Yup, both sides does take the torque, even though the right side may face more of it. With crossing on both sides, the right side may take 66% of the torque, while the left side might have 34%. With radial on the left, you'd end up making the right side take up 100% of the torque.
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Old 07-06-06, 07:29 AM
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Originally Posted by Al1943
Spokes with higher tension do less damage to hubs than spokes with lower tension. The lower tension spokes flex more. The thing about radial lacing is that stresses are carried directly toward and away from the hub whereas with tangential crossed lacing stresses are relieved on an angle and shared through the crossings. This is explained well in the Jobst Brandt book "The Bicycle Wheel".

I've always wondered if a 1-cross pattern could be the compromise that would preserve the warranty.

Al
More clearly, the hub flange has more material to support tension tangentially than it does radially. The danger is that the spokes under high tension could deform the flange, cracking it and pulling out radially. If you look at the shimano hubs that ARE made to accept radial lacing, there is a lot more material outside of the spoke holes.

110kgf equates to ~220 lbs of force pulling on each spoke. If you look at a hub flange and think about having one of your 220 lb friends hang from a spoke hole, it's a little scary -- especially if they start bouncing on it.
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