D
ahhh now i unnnerstan ping!! coool. i'll try the musical note
approach.
The following is from sheldonbrown parsec 1. a photo of brown
mangling spokes with a crowbar is missing here but is viewable at his
bicycle website
More informative dialogue comes by searching groups through the
sheldonbrown.com search boxes with the key words eg, spoke windup,
stress relief, sissy method, - often with the wheel devil hizelf at
the helm:
Spoke Torsion
As the wheel begins to come into tension, you start to have to deal
with spoke torsion. When you turn your spoke wrench, the first thing
that happens is that the spoke will twist a bit from the friction of
the threads. Once the nipple has turned far enough, the twist in the
spoke will give enough resistance that the threads will start to move,
but the spoke will remain twisted. What a good wheelbuilder can do
that a robot machine can't do is feel this twist. If you "finish" you
wheel up, and it is perfectly true in your stand, but the spokes are
twisted, the wheel will not stay true on the road. The twist in the
spokes will eventually work itself out, and the wheel will go out of
true.
This problem can be prevented by sensitive use of your spoke wrench.
What you need to do is overshoot and backlash. In other words, suppose
you want to tighten a particular spoke 1/4 turn. You don't just turn
the wrench 1/4 turn, you turn it a little farther, then back it up
that same little bit. The nipple winds up being 1/4 turn tighter, but
the backing up releases the twist in the spoke.
This is much easier to do on straight-gauge spokes, because they are
stiffer torsionally, and it is easier to feel the twist than it is
with butted spokes. This is one of the reasons I like "aerodynamic"
spokes so much; not so much for the aerodynamics, as for the fact that
you can tell visually if they are twisted.
Seating and Stress Relieving the Spokes
Before a wheel is ready for the road it must be stress relieved,
because the bend in the spoke has to accommodate itself to the shape
of the hub flange and vice versa, and a similar process may go on
where the nipple sits in the rim. Some wheelbuilders do this by
flexing the whole wheel, others by grabbing the spokes in groups of 4
and squeezing them together. My preferred technique is to use a lever
to bend the spokes around each other where they cross. My favorite
lever for this is an old left crank:
This particular technique has the added advantage of bending the
spokes neatly around each other at the crossing, so they run straight
from the crossing in both directions. As you go around the wheel this
way you will probably hear creaks and pinging sounds as the parts come
into more intimate terms with each other.
After you do this, you will probably have to do some touch-up truing,
then repeat the stressing process until it stops making noise and the
wheel stops going out of true.
Jobst Brandt , author of the excellent book The Bicycle Wheel points
out a less obvious benefit of this stressing of the spokes:
"...After cold forming, steel always springs back a certain amount
(spokes are entirely cold formed from wire). Spring-back occurs
because part of the material exceeded its elastic limit and part did
not. The disparate parts fight each other in tension and compression,
so that when the spoke is tensioned, it adds to the tensile stress
that can be, and often is, at yield.
"...When spokes are bent into place, they yield locally and addition
of tension guarantees that these places remain at yield. Because
metal, at or near the yield stress has a short fatigue life, these
stresses must be relieved to make spokes durable.
"...These peak stresses can be relieved by momentarily increasing
spoke tension (and stress), so that the high stress points of the
spoke yield and plastically deform with a permanent set. When the
stress relief force is relaxed these areas cannot spring back having,
in effect, lost their memory, and drop to the average stress of the
spoke."
If you have done this, you will wind up with a wheel that is true and
round, and will stay that way better than most machine made wheels. In
addition, you will have learned a lot about truing wheels, and you
will feel more like a real professional mechanic
approach.
The following is from sheldonbrown parsec 1. a photo of brown
mangling spokes with a crowbar is missing here but is viewable at his
bicycle website
More informative dialogue comes by searching groups through the
sheldonbrown.com search boxes with the key words eg, spoke windup,
stress relief, sissy method, - often with the wheel devil hizelf at
the helm:
Spoke Torsion
As the wheel begins to come into tension, you start to have to deal
with spoke torsion. When you turn your spoke wrench, the first thing
that happens is that the spoke will twist a bit from the friction of
the threads. Once the nipple has turned far enough, the twist in the
spoke will give enough resistance that the threads will start to move,
but the spoke will remain twisted. What a good wheelbuilder can do
that a robot machine can't do is feel this twist. If you "finish" you
wheel up, and it is perfectly true in your stand, but the spokes are
twisted, the wheel will not stay true on the road. The twist in the
spokes will eventually work itself out, and the wheel will go out of
true.
This problem can be prevented by sensitive use of your spoke wrench.
What you need to do is overshoot and backlash. In other words, suppose
you want to tighten a particular spoke 1/4 turn. You don't just turn
the wrench 1/4 turn, you turn it a little farther, then back it up
that same little bit. The nipple winds up being 1/4 turn tighter, but
the backing up releases the twist in the spoke.
This is much easier to do on straight-gauge spokes, because they are
stiffer torsionally, and it is easier to feel the twist than it is
with butted spokes. This is one of the reasons I like "aerodynamic"
spokes so much; not so much for the aerodynamics, as for the fact that
you can tell visually if they are twisted.
Seating and Stress Relieving the Spokes
Before a wheel is ready for the road it must be stress relieved,
because the bend in the spoke has to accommodate itself to the shape
of the hub flange and vice versa, and a similar process may go on
where the nipple sits in the rim. Some wheelbuilders do this by
flexing the whole wheel, others by grabbing the spokes in groups of 4
and squeezing them together. My preferred technique is to use a lever
to bend the spokes around each other where they cross. My favorite
lever for this is an old left crank:
This particular technique has the added advantage of bending the
spokes neatly around each other at the crossing, so they run straight
from the crossing in both directions. As you go around the wheel this
way you will probably hear creaks and pinging sounds as the parts come
into more intimate terms with each other.
After you do this, you will probably have to do some touch-up truing,
then repeat the stressing process until it stops making noise and the
wheel stops going out of true.
Jobst Brandt , author of the excellent book The Bicycle Wheel points
out a less obvious benefit of this stressing of the spokes:
"...After cold forming, steel always springs back a certain amount
(spokes are entirely cold formed from wire). Spring-back occurs
because part of the material exceeded its elastic limit and part did
not. The disparate parts fight each other in tension and compression,
so that when the spoke is tensioned, it adds to the tensile stress
that can be, and often is, at yield.
"...When spokes are bent into place, they yield locally and addition
of tension guarantees that these places remain at yield. Because
metal, at or near the yield stress has a short fatigue life, these
stresses must be relieved to make spokes durable.
"...These peak stresses can be relieved by momentarily increasing
spoke tension (and stress), so that the high stress points of the
spoke yield and plastically deform with a permanent set. When the
stress relief force is relaxed these areas cannot spring back having,
in effect, lost their memory, and drop to the average stress of the
spoke."
If you have done this, you will wind up with a wheel that is true and
round, and will stay that way better than most machine made wheels. In
addition, you will have learned a lot about truing wheels, and you
will feel more like a real professional mechanic