Join Date: Apr 2010
Location: Sunnyvale, CA USA
Mentioned: 3 Post(s)
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Originally Posted by Lone_rider
Finally after all these years I go out and buy myself a new Jamis Comp road bike and after 400 k. I am starting to break spokes about one every second ride and at 25 bucks a repair it is getting to expensive to ride. I has 14 gauge S/S spokes but I weigh in about 260 lb. Any thoughts about what I can do ( besides trying to lose more weight ) would be a great help
Your problems are poor build quality and a shop that knows little about wheels or has set you up as a repeat customer at $25 a pop (it's $40-$50 in labor to build or completely rebuild a wheel which would permanently resolve the problem). You need to either find a shop with a more skillful or honest wheel builder or learn the skills yourself. Jobst Brandt's _The Bicycle Wheel_ is good.
The issue here is that spokes fail due to fatigue, with the number of cycles they survive (about 750 per mile) dependent on average stress and the magnitude of the variation (a heavier person causes more variation).
Wheels which have not been stress relieved have parts of the elbows which were never taken past their elastic limit and therefore have high average stress. After enough cycles all those spokes (especially on the rear drive side) will fail about the same time.
Wheels with insufficient tension (especially in the rear non-drive side) can have the spokes going slack and bending with the high stress from bending creating premature failures. The low tension also allows nipples to rotate and loosen which exacerbates the problem and means the wheels don't stay true.
Your machine built wheels failed because they weren't stress relieved and may have had some spokes at excessive or insufficient tension. They would have probably survived if some one fixed that before you rode the bike.
The minimal fix is to replace all of the spokes in the side(s) which have been breaking (they all have the same number of fatigue cycles and about the same residual stress so the rest should be failing in short order) with DT or Wheelsmith 14/15 gauge double butted with brass nipples. Set drive side tension to an appropriate level like 110kgf. Tighten the non-drive side enough to center the wheel. Stress relieve. Correct any minor problems. Assuming you correctly compensated for spoke windup the wheel will stay true until you put a bend in it. The spokes will last pretty much indefinitely, through many rims (even if crashed).
Counter-intuitively, double-butted spokes which are thinner in the middle build into stronger wheels than straight-gauge spokes of the same thickness because the thinner center spans are stretchier resulting in less stress concentration at the elbows + threads and the rim can deform more before the spokes go slack leaving the rim unsupported laterally at which point it can collapse.
At 260 pounds you are exceeding the design spec of light-weight rims (under 160 pounds is a reasonable weight for bicycle racers) and are going to be more likely to bend when you run into pot-holes and other obstacles. You might consider switching to beefier rims at the same time, with reasonable spoke count (most people would recommend 36), and conventional cross-3 lacing.