From: BRANDT_JOBST/HP1900_01@HPLOMG.HPL.HP.COM
Newsgroups: rec.bicycles
Subject: Re: Hubs built for straight spokes
Date: 8 Sep 92 22:07:43 GMT

Tom Kunich writes:

> I have seen two basic kinds of failures in non-racing mountain bike
> wheels: Either they have been built with brittle japanese spokes
> or they have actually worn completely out.

Hold the ethnic slurs for a moment will you.  Among Japanese spokes
are some of the world's best as are other steel products like Tange
and Ishiwata bike tubing.  No one makes brittle spokes since they are
all cold formed, something not possible with brittle materials.  What
you perceive as brittle is most likely fatigue failure, if that is
what you saw.

> A very interesting case of the last was the bike of a large strong
> rider (a triathlete) who rode very much. He brought his wheels into
> a shop to have them rebuilt. The mechanic started to take off the
> freewheel and as he twisted the wheel backwards _all_ of the spokes
> on the drive side broke at once! Looking at the spokes, each was
> worn almost completely through where it transited the hub. They were
> so thin at this point that it was pretty hard to see how this guy
> could have been riding all that time. Just the week before he
> and I had ridden the Grand Finale Century and it went over Corral
> Hollow Rd, not a terrible climb, but the top part is steep enough
> that one would have thought the wheel would have failed.

I have seen a lot of wheels and many failures but this whole event
sounds like nothing I have ever seen nor can I visualize it.  First off,
did you see these spokes break?  Secondly is this figuratively speaking
or did all (or most) of the spokes break?  If so then this is an
impossibility because after half of them broke there would be no more
tension to break successive ones.  The hub shaft that is insignificantly
strong would fail in torsion next.

What seems even more implausible is that the spokes were worn thin
from the action of the hub.  Now, I know from prior discussions that you
can't plead mechanical innocence and change that to "spokes that were
cut by the chain".  So how did these spokes "wear" almost through,
considering that I have never been able to detect any wear on steel
spokes running in an aluminum hub?

> What I was talking about was the stress failures that commonly happen
> to road wheels with too small a spoke in them for the weight rider.
> And with all of the 'advice' these days about 32 (or even 28) 15 gauge
> spokes in road wheels it's easy to fall for the propaganda.

You're getting on thin ice here Tom, spokes in a wheel are stressed to
about 1/3 of their rupture stress and are only unloaded from the weight
of the rider.  They receive at most a 5% increase or decrease in stress
from braking or pedaling under the most extreme conditions.  Therefore,
this stress failure cannot occur but only a fatigue failure.  If it were
caused by too high a peak stress then the spokes should break the first
time the rider rides over a sharp bump or off a curb.

> After following Jobst's advice and using 36 spoke, 14-15-14 spokes
> or aero 32 spoke/double butted, I have seldom had trouble.

Sorry, agreeing with something I said won't get you off without first
explaining these extraordinary phenomena to which you alluded above.
Without further evidence I feel safe in relegating all of it to the myth
and lore department.  The whole story sounds like what one who is unclear
on the concepts might imagine happening... but it doesn't happen that way.

jobst_brandt@hplabs.hp.com
Newsgroups: rec.bicycles,rec.bicycles.misc