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Old 07-14-2008, 02:49 PM
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cachehiker cachehiker is offline
Motorized Bicycle Member
Join Date: Jul 2008
Location: Hyde Park / Logan, UT
Posts: 35
Default Re: Ripped Out a Spoke ?

I think you should ride with some of the Cat. 2's out here. 20+ mph sprints up a 6% grade is the norm if you want to keep up.

I'll admit to being a bit obsessive about my wheels but I would never clamp a sprocket on one without retensioning it. A properly tensioned and dished 36 spoke wheel will have 18 pulling spokes effectively sharing the load under acceleration. A poorly built wheel will have only 6 carrying 300% higher tension when accelerating at which point it becomes more likely that one will the pull through the spoke bed of the rim. It's generally one of the 12 spokes that are "just along for the ride" that snap at the bend or nipple due to metal fatigue.

IIRC, a good DT Swiss 14 gauge spoke will take about 400 lbs. before it's at risk of breaking. I tension the majority of my wheels to 240 lbs. At 25 mph, given a little quick and dirty +/-20% trigonometry, the 160 lb. margin equates to about 50 peak hp required for instantaneous spoke failure. For a poorly built wheel we're looking at 17 peak hp. The high cycle fatigue limit is generally about 35% of this or just 6 hp for a poorly built wheel as opposed to 18 hp for an ideally tensioned one at 25 mph.

I realize that I'm not taking the strength of the spoke bed into account but one of these has a generous safety margin for being powered with an 80cc motor. The other does not.

Last edited by cachehiker; 07-14-2008 at 03:50 PM.
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