[Yak] Spokes get brittle? Was "Single Wheel Trailer"
John S. Allen
jsallen at bikexprt.com
Fri Oct 10 23:37:35 CDT 2008
At 08:51 PM 10/10/2008, Harvey Sachs wrote:
>Mike Lindroos asked: <snipo> do spokes get brittle or anything with
>Spokes do fatigue and fail, eventually, but a properly built wheel
>will last for a very long time. Problem areas include the
>following: (1) Poor match between hub flange and spoke head. For
>example, using modern spokes, designed for pretty thick flanges,
>with older steel-flanged hubs, as on some classic bikes. This
>leaves the critical bend of the spoke out in thin air. Those of us
>who have been through this buy tiny brass washers to artifically
>thicken the flange to match the spoke.
Harvery, you know this but others might not: so, for all you novice
wheelbuilders out there building your first wheel on a hub with thin
flanges, the washer goes under the spoke head, to pull the elbow
against the flange.
>Other flange problems include over-sized holes that don't support
>the head well, and holes that aren't countersunk. BTW, if only one
>side is countersunk, that should get the bend, not the head. (2)
>Spoke tension issues, particularly overtightening to compensate for
>a warped or bent rim. (3) Overstressing from impact. Like potholes
>and railroad tracks.
>"Embrittlement" could be associated with chromed spokes, but these
>should be darned near extinct, having been largely replaced by
>stainless in the past 30 years.
Stainless steel spokes, now in almost universal use, are shiny too,
but it is my recollection that they fatigue (like bending a paperclip
bqck and forth till it breaks ) faster than carbon steel spokes, the
kind with the dull gray galvanized finish -- unfortunately also nearly extinct.
Very common contributors to spoke failure are wheels with too few
spokes (very popular nowadays), narrow spacing between flanges, and
overdished rear wheels. The spokes on the right side of a rear wheel,
at a steeper angle, have to be under more tension -- two or three
times as much as those on the left, with many modern wheels with 8,
9, 10, 11-sprocket cassettes. The spokes on the right break because
they are under high tension, and the ones on the left because they go
slack and work back and forth. BF has the advantage of a relatively
wide rear-dropout spacing, small wheels, which puts the spokes at a
better angle to resist side loads, and a good wheelbuilder!
John S. Allen
Regional Director for New York and New England, League of American Bicyclists
League Cycling Instructor #77-C and Member of the League's Education Committee
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