mCrux Wrote:
Last December I commuted 30 miles a day on an old Specialized Alle
Sport
that increasingly suffered from cracked chain stays. As the bike fel
apart,
the cheap generic spokes broke frequently and the RX-100 component
had
degraded to near uselessness.With patience and greasy hands at th
curbside,
I was able to keep up with replacing the breaking spokes for severa
weeks,
but with each broken spoke I got a close-up reality check on how fas
the
chain stays were giving way. Despite my crunch budget as a student
the
specter of catastrophic frame failure was not only enough for me t
keep my
speed below 20 mph, but also to fork over $1500 at the LBS for a ne
bike. I
depend upon the bike for transportation, and so this was the way t
go.

In January, I decided to buy a Redline Disc-R (disc-brake road bike
to
replace my commuter/road bike and I walked into a LBS that was suppose
to
be receiving one in my size, and I told the staff I was there to buy
The
shop promptly required a down payment, but I got a call later in th
week
and was told the bike was in the shop, assembled, tuned, and ready t
roll.
I showed up, saw the bike, and paid the balance. The sales perso
insisted
on wheeling the bike back to the mechanics' shop for a "final check t
be
sure everything is adjusted right." Seconds later, the sales perso
rolled
the bike back out to me on the showroom floor and announced the bik
was all
ready to go!

I took the bike home, and the next day I returned the wheels to the LB
to
have them re-tensioned because they were grossly out of true. Althoug
with
disc brakes the bike could function despite the wheel wobble, I wa
afraid
that if I rode the wheels in that condition it would ruin them. Th
rear
wheel actually had a 1/4" wobble. The mechanic was friendly, bu
dismissed
the wheel wobble problem as a minor one. In a couple minutes, he mad
spoke
adjustments that significantly reduced the wheel wobble, and h
explained it
was not necessary to re-tension the wheels because all the spokes wer
at a
similar amount of tension.

Four months later, while I sat on a park bench next to the bike,
heard a
spoke snap. It seemed really strange for a spoke to break when th
bike
wasn't being ridden, but I recalled having just gone over a series of
stutter bumps and I attributed thermal expansion of the rim to be th
final
straw since it was the first hot sunny day of the season. At the sam
time,
the wheels had never been subjected to any hard collisions with curb
or
potholes or anything like that, so I was concerned by the implication
of
this spontaneous failure. Coincidentally, I was only two blocks awa
from
the shop where I purchased the bike.

After buying the bike, in aversion to the original bright red finis
and the
many "steal-me" decals, I repainted the frame. When I wheeled it int
the
shop, nobody realized it was originally purchased there only a fe
months
earlier. The shop's mechanic explained the spoke snapped because th
spokes
were badly tensioned and of cheap generic quality. The shop had no
replacement spokes of correct length, and therefore sent me to a siste
shop
located several blocks away. At the sister shop, I got the sam
explanation:
'Bad work, bad parts.'

The next day, I took the wheel to a different shop and learned th
spokes
are of brand quality (Sapim) but that they were all extremely over
tightened. The mechanic at this shop expressed amazement that the whee
was
surviving the high tension of the spokes. I asked him to re-tensio
the
wheel, but the mechanic refused, saying the wheel was ruined and al
he
could do was replace the spoke and make some adjustments to minimiz
the hop
caused by the wheel damage and help me get a few more miles befor
having to
replace the wheel.

I had truthfully told the mechanic that I'd never taken a spoke wrenc
to
the wheel, nor hit anything with it, but the mechanic doubted my
veracity.
He insisted I must have hit something really hard with the wheel and
then
tried to fix it myself and caused further damage. Then he asked if I'd
gotten the bike serviced since I bought it. I told him the truth and
he
decided that the spokes were too tight because I had not taken the bike
in
for a complete tune up after the first few hundred miles.

I admit I privately disbelieved the statement that the spokes could
have
spontaneously self-tightened to the point of extreme tension, but the
mechanic did provide convincing information that lead me to the
following
conclusions: One, the wheel had been poorly built because the spokes
were
way too tight. Two, this condition of excessive tension caused damage
and
resulted in reduced life expectancy for the wheel. Three, I'd likely
have to
replace the rim and spokes soon.

As it has turned out, no more spokes have broken on this wheel in the
2,000
miles covered since the spontaneous spoke failure. Not all is hunky
dory,
however. Over time, it appears that the rim is actually drifting to
the
left, affecting the wheel alignment in the frame. When the bike was
new, I
observed the wheel was centered in the frame stays. Now, the bike has
started to track a little bit to the right. Any ride of over 50 miles
now
causes a bit of pain on left side of my groin, as if I were sitting
off-center over the nose of the saddle, and the bike no longer has the
no-hands stability that is used to have.

When I dismount and take a closer look, I can see things that don't add
up
right. The tire is visibly offset in the chain stays by an 1/8 of an
inch;
that is, the gap between the rim and the chain stay on the right is
1/4"
greater than the gap on the left! At first, I was afraid the
misalignment
was a frame problem, but string-line measurements indicate the frame
is
actually pretty straight. Next, I was worried about the dropouts, and
wondered if they are tweaked-out somehow. So I borrowed and installed a
new
wheel, just to see how the alignment looks with that, and observe no
indications of alignment problems with the new wheel installed.

Now, here is my theory: The spokes on the cassette side are the
tightest, of
course, since they are shorter to accommodate the dish of the wheel. In
the
alleged over-tensioned state, these spokes are stretching under the
cyclic
stressing of normal use. As the right-side spokes now yield to the
excessive
tension, the left-side spokes apparently are contracting as the
yielding
spokes effectively grow longer. The change in effective spoke length
is
enough to shift the rim to the left 1/8" and this is why the wheel is
now
1/4" closer to the left chain stay, compared to its distance from the
right
chain stay.

When I ride the bike, this offset of the rear wheel requires
compensation by
the direction of the front wheel or by the camber of tires exerted by
leaning the bicycle slightly to the left. As such, the bike is
generally
tilted to the side and therefore I really do sit with extra pressure on
the
left side of my groin and the bike really is no longer as balanced and
stable when underway.

Comments? Recommendations?

mykal in Seattle

Take the wheel to a wheel builder that is trustworthy.
Ask for a little instruction as well as the required adjustment(s).
The instruction should include:
1. his or her use of a centering tool or at least a truing stand the
is stable. You can see the same thing in your frame by flipping the
wheel over and looking at the centering.
2. A spoke tension gague on each spoke and write down the readings and
what they convert to based on your spokes
3. A lesson in how to tension relieve.

You can learn all this on your own by reading "the Bicycle Wheel" by
Jobst Brandt. Most library systems have the book and you can by it
through most bicycle shops.


--
daveornee