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#1
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front dynohub - wheel building
i'm trying to calculate the spoke length for a wheel with a front
sturmey archer dynohub and a sun CR18 26x1-3/8 rim. in the instructions for wheel building http://www.rickadee.net/~zephyrus/ad4935/ad4935.html (thanks!) they write that the rim should be off-centre. does anyone know the reason for that and how much off should it be? better still, the exact lengths of the spokes? dan |
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#2
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Dan Limon writes:
I'm trying to calculate the spoke length for a wheel with a front Sturmey archer dynohub and a sun CR18 26x1-3/8 rim. In the instructions for wheel building: http://www.rickadee.net/~zephyrus/ad4935/ad4935.html they write that the rim should be off-centre. Does anyone know the reason for that and how much off should it be? Better still, the exact lengths of the spokes? Use the standard spoke length programs available on the web and enter cross zero for the lacing pattern. The 'dish' of the wheel is immaterial to spoke length, the cosine of small angles being essentially one. The offset will develop itself as you center the rim between the locknuts on the axle as is standard for wheels. Jobst Brandt |
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Jeff Wills writes:
Use the standard spoke length programs available on the web and enter cross zero for the lacing pattern. The 'dish' of the wheel is immaterial to spoke length, the cosine of small angles being essentially one. The offset will develop itself as you center the rim between the locknuts on the axle as is standard for wheels. Dan- Damon Rinard's Spocalc has values for many hubs and rims already in place. I checked mine (an older download) and it has values for the Sturmey Dynohub and a Sun CR20 rim. If those aren't close enough, you can measure the rim yourself and manually input values. It's available at: http://www.sheldonbrown.com/rinard/spocalc.htm As Jobst says, any asymmetry will resolve itself as you true the wheel. Jobst- why "cross zero"? Surely you aren't recommending he build the wheel radially. The keyhole spoke holes on the small flange would make it difficult to keep the wheel tensioned and true, I think. I don't see any reason to cross lace spokes on a steel flange of that diameter. I have one like that and the small flange should be cross three so that the double keyhole spoke holes in the hub will give their best support to the spokes. Jobst Brandt |
#5
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wrote: I don't see any reason to cross lace spokes on a steel flange of that diameter. I have one like that and the small flange should be cross three so that the double keyhole spoke holes in the hub will give their best support to the spokes. Jobst Brandt OK- radial on the large flange side, 3X on the small flange. It'll look cool! FWIW: there's a drum-braked single-speed cruiser running around town with a radial-spoked front wheel. I don't think it gets heavy braking on that wheel... Jeff |
#6
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Quoth Jobst Brandt:
[Sturmey-Archer DynoHub with huge flange on one side] I don't see any reason to cross lace spokes on a steel flange of that diameter. I have one like that and the small flange should be cross three so that the double keyhole spoke holes in the hub will give their best support to the spokes. There's no techincal reason, but as a practical matter, it may be difficult to find appropriate length spokes for this at a typical LBS. Sheldon "253 mm?" Brown +----------------------------------------+ | The race is not always to the swift, | | nor the battle to the strong | | -but that's the way to bet. | | --Damon Runyon | +----------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide http://captainbike.com http://sheldonbrown.com |
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