Wheelbuilding issues

So I'm trying to build my first rear derailer wheel that's actually up
to the maximum safe level of tension the rim can handle. In the past I
have built 1 front wheel, 1 rear derailer wheel, and 2 dishless rear
wheels. These came out okay but not as high-tension and windup-free as
possible.

I'm using a new 36-hole 700C Sun CR-18 (575 grams, 23mm
outside/18mm-ish inside width, eyelets not sockets, brushed), straight
2mm spokes (Sapim on one side and DT on the other due to an ordering
error, and I didn't have the money for butted or I would have gotten
them), brass Sapim nipples, and a new LX rear hub. This is going to be
a 9-speed wheel for commuting, distance riding and loaded touring. I
know all about how much 9-speed sucks strength-wise and am partially
just building a 9-speed wheel and setting my bike up 9-speed to get a
feel for how well such highly dished wheels can hold up. I have read
The Bicycle Wheel and Sheldon Brown's wheelbuilding page several
times. I'm using a tensiometer to check for inordinately loose/tight
spokes, balanced tension, and to establish a standard for how much
tension my future wheels with CR-18s can handle.

I laced the wheel 3-cross using Tri-Flow to lube the spoke threads and
white grease on the nipple seats. I accidentally dunked the non-drive
side spoke threads in lube before I remembered not to (as advised on
Sheldon's page), so I wiped a bunch of lube off with a rag and decided
to see how the wheel would fare longevity-wise with lightly lubed
non-drive spokes.

The first mistake I made was overestimating how much tension this rim
could take before beginning to overload and go potato-chip-shaped
(this is also a reason I didn't just use degreaser on the lubed
non-drive-side spoke threads - you wouldn't really have to worry about
that with a strong enough rim even if it was highly dished, right?).
In fact, I was a bit under the impression that with this rim I
wouldn't be able to get the tension that high up at all before nipples
started getting impossible to turn. This was a big mistake, I know
now, but there is not exactly much material out there about learning
to predict exactly what rims will be over-tensionable and which won't
be, even though there are hints that such a clear distinction exists.
Anyway, during what I then thought was not quite the end of the
building process, I checked the wheel's centering and discovered the
rim needed to be pulled over to the drive side by quite a bit. The
drive side spokes were at I think (can't remember exactly) about
100-110 KgF average. At this point, the rim was true laterally and was
mostly true radially and tension balanced with a few exceptions (see
below). I figured it would be safe at this point to make the centering
adjustement by just tightening all the drive-side spokes a half-turn,
rather than loosening the non-drive spokes and tightening the drive
ones. So I did that and when I spun the wheel immediately afterwards
to check for typical small necessary lateral truing corrections,
instead I saw that the wheel had become fairly potato-chip shaped. Up
to this point I had not been following The Bicycle Wheel's procedure
of adding layers of tension and then stress relieving to check for how
close one is to approaching the rim's maximum safe tension - again, I
didn't think it was really necessary with this rim to do so yet. After
this occurred, I backed off all the drive-side spoke tensions by the
half-turn I had just added. The potato chip shape remained. Then I
backed off the tension by I think a quarter turn on both sides and it
still remained. Afraid that I had permanently warped the rim, because
the wheel didn't go back to being true, I then removed all tension
from the spokes and reset them to the initial stage with the spoke
threads just barely covered by the nipple, added a small amount of
tension, did some very minor truing that one always needs to do at the
beginning tensioning/truing phases, and saw that the rim was just as
true as it was at this point the first time through, leading me to
believe that my over-tensioning did not permanently warp the rim. The
small bits of truing necessary did not match the shape of a slightly
collapsed rim.

My questions about this episode a If the rim was not permanently
warped, what exactly is the reason that it did not go back to its
previous true shape after I removed the tension I just added, and then
some? I assume now that this is the same reason why a rim that's just
gotten stress-relieved enough to overload it, as per The Book, will
remain in the slight potato-chip shape even after you stop squeezing
it, right? In later attempts at building this wheel, I added a
quarter-turn layer of tension, stress-relieved it all around, saw a
very slight potato-chip shape of maybe 2mm away from the centerline on
either side happening as I spun the wheel in the stand, backed it off
a half turn on both sides, all as per The Bicycle Wheel, and the
result after the de-tensioning was that it was about as true as it was
prior to the last additional tension layer. On the initial build, if
after my overtensioning I had just backed off the tension all around a
bit more instead of starting over, would the wheel have gone back to
trueness, presuming that all my nipple-turning had been accurate
enough? Does it depend on exactly how overloaded and deformed the rim
became? In The Book, it says that after you overload a rim during
stress relieving, some truing will be necessary after you back it off
half a turn all around. But none of the potato-chip shape from
overloading is supposed to be remaining at that point, right? If it
was, and you trued the rim in reaction to that, wouldn't everything
just get really screwed up? So is the truing you'll be needing to do
at that point just in reaction to inaccuracies in your nipple-turning?
How exactly do all the rules about all this apply to rims of different
types and weights? When you stress relieve a rim to test it for
overload, are you supposed to be watching the rim for a potato-chip
shape happening as you squeeze each group of 4 spokes and then stop if
you see one, or should you just go through and stress relieve all the
spokes and then check to see if the deformation occured somewhere in
the process?

There was another time when I stress relieved all around and then saw
that the rim was in a shape that resembled the slight potato
chip/saddle shape of an overloaded rim, but not quite. Whereas the
usual shape is a series of curves where there's an apex veering to the
left, followed by an apex veering to the right 90 degrees later, and
an apex to the left another 90 degrees from that, etc. this series of
curves went more like apex to the left followed by one to the right 45
degrees later, followed by the next one to the left 135 degrees later,
followed by one to the right 45 degrees later, etc, such that both
curves going to one side were still 180 degrees from each other, but
the overall shape was weird. Again, this was after I tensioned and
stress relieved the wheel. I figured that this was just a sign of
overload but am still not really sure if I'm missing something. Does
rim deformation just happen this way sometimes? Are there other
variations on the typical imploded-rim shape?

When stress relieving spokes, all internal stresses are relieved after
you make one complete round of squeezing adjacent spokes beyond yield,
right? If so, does that mean that if you were building up a rim that
you absolutely knew was strong enough that difficulty in turning
nipples was going to be the tension bottleneck for the wheel, you
would only really have to stress relieve once, when you hit the point
where no more tension can be added?

I'm also wondering about how exactly techniques to eliminate spoke
windup work. When you overshoot a quarter turn and then back up to
eliminate windup, is the idea that somewhere in that extra quarter
turn, the spoke's increasing torsional load will become enough to
overcome the amount of friction between its threads and those of the
nipple? What exactly keeps the spoke from winding up in the other
direction when you back up the nipple? When you go to back up the
nipple, isn't there just going to be more friction than you started
with because now the spoke is tighter by a quarter turn plus whatever
adjustment you wanted to make? Is it the best idea to keep one hand on
the spoke you're adjusting as the other turns the spoke wrench, so
that you can feel when a spoke is winding up and when it unwinds? Is
it possible for a spoke to only unwind partially?

I'm also wondering why hardly anything I've read about wheelbuilding
mentions the possibility of tightening drive vs. non-drive-side spokes
according to a ratio based on how much they pull the rim due to their
differing angles, and how much tension each side will have in total
when the wheel is done. The ratio is something like 8:5 for most
9-speed rears, isn't it? So why not just do your tensioning layers and
truing adjustments by turning the drive side something like twice as
much all the way through? If you just act like both sides pull the
same amount and therefore you make even increments on both sides when
you're tensioning, dishing, or truing, aren't you bound to create
lateral/dish errors that must be dealt with using the same flawed
process? I was experimenting with this and it seems like there may be
something to it, but this time around I was confused about enough
things that throwing this in the mix was more than I really wanted to
deal with.

In The Bicycle Wheel, it's written that wheels with unbalanced spoke
tensions will equalize themselves in use. Is this just for the obvious
reason that the spokes with low tensions will get looser and out of
true in use, which causes all sorts of havoc, or is there something
subtle I'm missing here that causes problems when some spokes are also
inordinately high in tension, other than increasing the likelihood of
eyelet cracking? Does this imply, for example, that a wheel with
generally closely balanced, high tensions but a few spokes at
inordinately high tensions for some reason would all equalize in use?

A final group of questions has to do with interactions between radial
trueness, tension balancing, and rim imperfections. I got my wheel to
a point several times where the total tension difference between the
slackest and tightest drive-side spokes was about 30 KgF, with a few
at about 95, a few at about 125-130, and most at about 105-120, and a
similar bunch of disparities on the non-drive-side. This was at about
the max safe tension for the rim using the Jobst method unless I'm
very confused. There was still quite a bit of radial truing error,
perhaps 1mm between high and low points, but it was arranged in the
classic annoying pattern where the bumps are tighter spots and the
dips are looser spots. In other words, if I just went through and made
the tension on each spoke exactly the same without regard to how true
it would make the wheel, then the wheel would be a total mess. I was
left with the definite feeling that I was just encountering
imperfections in the rim, since I worked on it for a long and it
seemed like there was little further I could do without compromising
either tension balance or reasonable trueness. On the other hand, I'm
fairly new at this and I don't want to put undue blame on the rim. My
question is just how bad are the tolerances on Sun rims, or CR-18s in
particular for those who have lots of experience with them, and what
kind of tension disparities do you usually end up with?

Thanks for reading and replying,
Nate Knutson

On 7 May 2004 21:54:04 -0700, (Nate Knutson)
wrote:

[snip]

When stress relieving spokes, all internal stresses are relieved after
you make one complete round of squeezing adjacent spokes beyond yield,
right? If so, does that mean that if you were building up a rim that
you absolutely knew was strong enough that difficulty in turning
nipples was going to be the tension bottleneck for the wheel, you
would only really have to stress relieve once, when you hit the point
where no more tension can be added?


[snip]

Nate Knutson

Dear Nate,

One source of confusion concerning the stress relieving techniques
advocated on rec.bicycles.tech may be the fact that most spokes are
made of stainless steel, which has no clearly defined yield point.

The example of a stress-strain curve with a marked dip that shows a
clear yield point in Jobst's book is not from a stainless steel spoke,
as can be seen by comparing it to the eight curves in his book's
appendix for stress-strain measurements performed on actual
spokes--they climb smoothly until they begin to stretch like taffy,
without any yield-dip.

In this respect, stainless steel resembles aluminum, not normal steel.

Carl Fogel

there's too much confusion about this "as much tension as the rim can
handle" business. maximum tension is a technical specification defined
by the rim manufacturer. exceeding it does not make the wheel stronger
or stiffer - because the spoke modulus remains the same regardless of
tension. excess tension can also lead to accelerated rim cracking.

call sun for clarification, but tension in the range of 90-100 kgf on
the sprocket side is more likely to be maximum spec.

/even/ tension is more important that absolute tension. read sheldon's
great article on wheelbuilding on how to get it right.


Nate Knutson wrote:
So I'm trying to build my first rear derailer wheel that's actually up
to the maximum safe level of tension the rim can handle. In the past I
have built 1 front wheel, 1 rear derailer wheel, and 2 dishless rear
wheels. These came out okay but not as high-tension and windup-free as
possible.

I'm using a new 36-hole 700C Sun CR-18 (575 grams, 23mm
outside/18mm-ish inside width, eyelets not sockets, brushed), straight
2mm spokes (Sapim on one side and DT on the other due to an ordering
error, and I didn't have the money for butted or I would have gotten
them), brass Sapim nipples, and a new LX rear hub. This is going to be
a 9-speed wheel for commuting, distance riding and loaded touring. I
know all about how much 9-speed sucks strength-wise and am partially
just building a 9-speed wheel and setting my bike up 9-speed to get a
feel for how well such highly dished wheels can hold up. I have read
The Bicycle Wheel and Sheldon Brown's wheelbuilding page several
times. I'm using a tensiometer to check for inordinately loose/tight
spokes, balanced tension, and to establish a standard for how much
tension my future wheels with CR-18s can handle.

I laced the wheel 3-cross using Tri-Flow to lube the spoke threads and
white grease on the nipple seats. I accidentally dunked the non-drive
side spoke threads in lube before I remembered not to (as advised on
Sheldon's page), so I wiped a bunch of lube off with a rag and decided
to see how the wheel would fare longevity-wise with lightly lubed
non-drive spokes.

The first mistake I made was overestimating how much tension this rim
could take before beginning to overload and go potato-chip-shaped
(this is also a reason I didn't just use degreaser on the lubed
non-drive-side spoke threads - you wouldn't really have to worry about
that with a strong enough rim even if it was highly dished, right?).
In fact, I was a bit under the impression that with this rim I
wouldn't be able to get the tension that high up at all before nipples
started getting impossible to turn. This was a big mistake, I know
now, but there is not exactly much material out there about learning
to predict exactly what rims will be over-tensionable and which won't
be, even though there are hints that such a clear distinction exists.
Anyway, during what I then thought was not quite the end of the
building process, I checked the wheel's centering and discovered the
rim needed to be pulled over to the drive side by quite a bit. The
drive side spokes were at I think (can't remember exactly) about
100-110 KgF average. At this point, the rim was true laterally and was
mostly true radially and tension balanced with a few exceptions (see
below). I figured it would be safe at this point to make the centering
adjustement by just tightening all the drive-side spokes a half-turn,
rather than loosening the non-drive spokes and tightening the drive
ones. So I did that and when I spun the wheel immediately afterwards
to check for typical small necessary lateral truing corrections,
instead I saw that the wheel had become fairly potato-chip shaped. Up
to this point I had not been following The Bicycle Wheel's procedure
of adding layers of tension and then stress relieving to check for how
close one is to approaching the rim's maximum safe tension - again, I
didn't think it was really necessary with this rim to do so yet. After
this occurred, I backed off all the drive-side spoke tensions by the
half-turn I had just added. The potato chip shape remained. Then I
backed off the tension by I think a quarter turn on both sides and it
still remained. Afraid that I had permanently warped the rim, because
the wheel didn't go back to being true, I then removed all tension
from the spokes and reset them to the initial stage with the spoke
threads just barely covered by the nipple, added a small amount of
tension, did some very minor truing that one always needs to do at the
beginning tensioning/truing phases, and saw that the rim was just as
true as it was at this point the first time through, leading me to
believe that my over-tensioning did not permanently warp the rim. The
small bits of truing necessary did not match the shape of a slightly
collapsed rim.

My questions about this episode a If the rim was not permanently
warped, what exactly is the reason that it did not go back to its
previous true shape after I removed the tension I just added, and then
some? I assume now that this is the same reason why a rim that's just
gotten stress-relieved enough to overload it, as per The Book, will
remain in the slight potato-chip shape even after you stop squeezing
it, right? In later attempts at building this wheel, I added a
quarter-turn layer of tension, stress-relieved it all around, saw a
very slight potato-chip shape of maybe 2mm away from the centerline on
either side happening as I spun the wheel in the stand, backed it off
a half turn on both sides, all as per The Bicycle Wheel, and the
result after the de-tensioning was that it was about as true as it was
prior to the last additional tension layer. On the initial build, if
after my overtensioning I had just backed off the tension all around a
bit more instead of starting over, would the wheel have gone back to
trueness, presuming that all my nipple-turning had been accurate
enough? Does it depend on exactly how overloaded and deformed the rim
became? In The Book, it says that after you overload a rim during
stress relieving, some truing will be necessary after you back it off
half a turn all around. But none of the potato-chip shape from
overloading is supposed to be remaining at that point, right? If it
was, and you trued the rim in reaction to that, wouldn't everything
just get really screwed up? So is the truing you'll be needing to do
at that point just in reaction to inaccuracies in your nipple-turning?
How exactly do all the rules about all this apply to rims of different
types and weights? When you stress relieve a rim to test it for
overload, are you supposed to be watching the rim for a potato-chip
shape happening as you squeeze each group of 4 spokes and then stop if
you see one, or should you just go through and stress relieve all the
spokes and then check to see if the deformation occured somewhere in
the process?

There was another time when I stress relieved all around and then saw
that the rim was in a shape that resembled the slight potato
chip/saddle shape of an overloaded rim, but not quite. Whereas the
usual shape is a series of curves where there's an apex veering to the
left, followed by an apex veering to the right 90 degrees later, and
an apex to the left another 90 degrees from that, etc. this series of
curves went more like apex to the left followed by one to the right 45
degrees later, followed by the next one to the left 135 degrees later,
followed by one to the right 45 degrees later, etc, such that both
curves going to one side were still 180 degrees from each other, but
the overall shape was weird. Again, this was after I tensioned and
stress relieved the wheel. I figured that this was just a sign of
overload but am still not really sure if I'm missing something. Does
rim deformation just happen this way sometimes? Are there other
variations on the typical imploded-rim shape?

When stress relieving spokes, all internal stresses are relieved after
you make one complete round of squeezing adjacent spokes beyond yield,
right? If so, does that mean that if you were building up a rim that
you absolutely knew was strong enough that difficulty in turning
nipples was going to be the tension bottleneck for the wheel, you
would only really have to stress relieve once, when you hit the point
where no more tension can be added?

I'm also wondering about how exactly techniques to eliminate spoke
windup work. When you overshoot a quarter turn and then back up to
eliminate windup, is the idea that somewhere in that extra quarter
turn, the spoke's increasing torsional load will become enough to
overcome the amount of friction between its threads and those of the
nipple? What exactly keeps the spoke from winding up in the other
direction when you back up the nipple? When you go to back up the
nipple, isn't there just going to be more friction than you started
with because now the spoke is tighter by a quarter turn plus whatever
adjustment you wanted to make? Is it the best idea to keep one hand on
the spoke you're adjusting as the other turns the spoke wrench, so
that you can feel when a spoke is winding up and when it unwinds? Is
it possible for a spoke to only unwind partially?

I'm also wondering why hardly anything I've read about wheelbuilding
mentions the possibility of tightening drive vs. non-drive-side spokes
according to a ratio based on how much they pull the rim due to their
differing angles, and how much tension each side will have in total
when the wheel is done. The ratio is something like 8:5 for most
9-speed rears, isn't it? So why not just do your tensioning layers and
truing adjustments by turning the drive side something like twice as
much all the way through? If you just act like both sides pull the
same amount and therefore you make even increments on both sides when
you're tensioning, dishing, or truing, aren't you bound to create
lateral/dish errors that must be dealt with using the same flawed
process? I was experimenting with this and it seems like there may be
something to it, but this time around I was confused about enough
things that throwing this in the mix was more than I really wanted to
deal with.

In The Bicycle Wheel, it's written that wheels with unbalanced spoke
tensions will equalize themselves in use. Is this just for the obvious
reason that the spokes with low tensions will get looser and out of
true in use, which causes all sorts of havoc, or is there something
subtle I'm missing here that causes problems when some spokes are also
inordinately high in tension, other than increasing the likelihood of
eyelet cracking? Does this imply, for example, that a wheel with
generally closely balanced, high tensions but a few spokes at
inordinately high tensions for some reason would all equalize in use?

A final group of questions has to do with interactions between radial
trueness, tension balancing, and rim imperfections. I got my wheel to
a point several times where the total tension difference between the
slackest and tightest drive-side spokes was about 30 KgF, with a few
at about 95, a few at about 125-130, and most at about 105-120, and a
similar bunch of disparities on the non-drive-side. This was at about
the max safe tension for the rim using the Jobst method unless I'm
very confused. There was still quite a bit of radial truing error,
perhaps 1mm between high and low points, but it was arranged in the
classic annoying pattern where the bumps are tighter spots and the
dips are looser spots. In other words, if I just went through and made
the tension on each spoke exactly the same without regard to how true
it would make the wheel, then the wheel would be a total mess. I was
left with the definite feeling that I was just encountering
imperfections in the rim, since I worked on it for a long and it
seemed like there was little further I could do without compromising
either tension balance or reasonable trueness. On the other hand, I'm
fairly new at this and I don't want to put undue blame on the rim. My
question is just how bad are the tolerances on Sun rims, or CR-18s in
particular for those who have lots of experience with them, and what
kind of tension disparities do you usually end up with?

Thanks for reading and replying,
Nate Knutson

(Nate Knutson) wrote in message . com...
In The Bicycle Wheel, it's written that wheels with unbalanced spoke
tensions will equalize themselves in use.

I thought I'd add pre-emptively that this is not the phrasing used in
the book, but just how I read and remember it. I can't post a direct
quote here because I don't have a copy with me. But it's still
something along these lines that I don't understand as it applies to
inordinately highly-tensioned rather than loose spokes, if that's
indeed the implication of whatever the exact quote is.

"Nate Knutson" wrote in message
om...
(Nate Knutson) wrote in message
. com...
In The Bicycle Wheel, it's written that wheels with unbalanced spoke
tensions will equalize themselves in use.

I thought I'd add pre-emptively that this is not the phrasing used in
the book, but just how I read and remember it. I can't post a direct
quote here because I don't have a copy with me.

I don't understand how that could be. The tightest spokes are the least
likely to loosen, and the loosest spokes are the most likely to loosen.

I don't recall reading anything like that in The Book.

Art Harris

Arthur Harris wrote:

"Nate Knutson" wrote in message
om...
(Nate Knutson) wrote in message
. com...
In The Bicycle Wheel, it's written that wheels with unbalanced spoke
tensions will equalize themselves in use.

I thought I'd add pre-emptively that this is not the phrasing used in
the book, but just how I read and remember it. I can't post a direct
quote here because I don't have a copy with me.

I don't understand how that could be. The tightest spokes are the least
likely to loosen, and the loosest spokes are the most likely to loosen.

I don't recall reading anything like that in The Book.

Page 105 of the third edition, under Balancing Tension:

"If spokes are not equally tight they will equalize during use and cause
misalignment."

--
Warren Block * Rapid City, South Dakota * USA

"Arthur Harris" writes:

"Nate Knutson" wrote
In The Bicycle Wheel, it's written that wheels with unbalanced
spoke tensions will equalize themselves in use.

I thought I'd add pre-emptively that this is not the phrasing used
in the book, but just how I read and remember it. I can't post a
direct quote here because I don't have a copy with me.

I don't understand how that could be. The tightest spokes are the
least likely to loosen, and the loosest spokes are the most likely to
loosen.

I don't recall reading anything like that in The Book.

Nate is right. According to page 111 of the German edition Jobst writes
(translated back to English): "If the spokes are unequally tensioned,
these differences will even out in use and the wheel will come untrue."
I don't understand it either.

Christian

Christian Odenthal writes:

In The Bicycle Wheel, it's written that wheels with unbalanced
spoke tensions will equalize themselves in use.

I thought I'd add pre-emptively that this is not the phrasing used
in the book, but just how I read and remember it. I can't post a
direct quote here because I don't have a copy with me.

I don't understand how that could be. The tightest spokes are the
least likely to loosen, and the loosest spokes are the most likely to
loosen.

I don't recall reading anything like that in The Book.

Nate is right. According to page 111 of the German edition Jobst
writes (translated back to English): "If the spokes are unequally
tensioned, these differences will even out in use and the wheel will
come untrue." I don't understand it either.

The spokes will not change but the rim will, assuming the wheel runs
over average bumpy roads that momentarily impart high stress to the
rim. Under these conditions, the rim will gradually conform to
tension distribution and thereby change individual preloads of the
spokes. The rim adapts and this alters spoke tension.

Jobst Brandt

Nate Knutson wrote:
So I'm trying to build my first rear derailer wheel that's actually
up to the maximum safe level of tension the rim can handle. In the
past I have built 1 front wheel, 1 rear derailer wheel, and 2
dishless rear wheels. These came out okay but not as high-tension and
windup-free as possible.
I'm using a new 36-hole 700C Sun CR-18 (575 grams, 23mm outside/18mm-
ish inside width, eyelets not sockets, brushed), straight 2mm spokes
(Sapim on one side and DT on the other due to an ordering error, and I
didn't have the money for butted or I would have gotten them), brass
Sapim nipples, and a new LX rear hub. This is going to be a 9-speed
wheel for commuting, distance riding and loaded touring. I know all
about how much 9-speed sucks strength-wise and am partially just
building a 9-speed wheel and setting my bike up 9-speed to get a feel
for how well such highly dished wheels can hold up. I have read The
Bicycle Wheel and Sheldon Brown's wheelbuilding page several times. I'm
using a tensiometer to check for inordinately loose/tight spokes,
balanced tension, and to establish a standard for how much tension my
future wheels with CR-18s can handle.
I laced the wheel 3-cross using Tri-Flow to lube the spoke threads and
white grease on the nipple seats. I accidentally dunked the non-drive
side spoke threads in lube before I remembered not to (as advised on
Sheldon's page), so I wiped a bunch of lube off with a rag and decided
to see how the wheel would fare longevity-wise with lightly lubed non-
drive spokes.
The first mistake I made was overestimating how much tension this rim
could take before beginning to overload and go potato-chip- shaped (this
is also a reason I didn't just use degreaser on the lubed non-drive-side
spoke threads - you wouldn't really have to worry about that with a
strong enough rim even if it was highly dished, right?). In fact, I was
a bit under the impression that with this rim I wouldn't be able to get
the tension that high up at all before nipples started getting
impossible to turn. This was a big mistake, I know now, but there is not
exactly much material out there about learning to predict exactly what
rims will be over-tensionable and which won't be, even though there are
hints that such a clear distinction exists. Anyway, during what I then
thought was not quite the end of the building process, I checked the
wheel's centering and discovered the rim needed to be pulled over to the
drive side by quite a bit. The drive side spokes were at I think (can't
remember exactly) about 100-110 KgF average. At this point, the rim was
true laterally and was mostly true radially and tension balanced with a
few exceptions (see below). I figured it would be safe at this point to
make the centering adjustement by just tightening all the drive-side
spokes a half-turn, rather than loosening the non-drive spokes and
tightening the drive ones. So I did that and when I spun the wheel
immediately afterwards to check for typical small necessary lateral
truing corrections, instead I saw that the wheel had become fairly potato-
chip shaped. Up to this point I had not been following The Bicycle
Wheel's procedure of adding layers of tension and then stress relieving
to check for how close one is to approaching the rim's maximum safe
tension - again, I didn't think it was really necessary with this rim to
do so yet. After this occurred, I backed off all the drive-side spoke
tensions by the half-turn I had just added. The potato chip shape
remained. Then I backed off the tension by I think a quarter turn on
both sides and it still remained. Afraid that I had permanently warped
the rim, because the wheel didn't go back to being true, I then removed
all tension from the spokes and reset them to the initial stage with the
spoke threads just barely covered by the nipple, added a small amount of
tension, did some very minor truing that one always needs to do at the
beginning tensioning/truing phases, and saw that the rim was just as
true as it was at this point the first time through, leading me to
believe that my over-tensioning did not permanently warp the rim. The
small bits of truing necessary did not match the shape of a slightly
collapsed rim.
My questions about this episode a If the rim was not permanently
warped, what exactly is the reason that it did not go back to its
previous true shape after I removed the tension I just added, and then
some? I assume now that this is the same reason why a rim that's just
gotten stress- relieved enough to overload it, as per The Book, will
remain in the slight potato-chip shape even after you stop squeezing it,
right? In later attempts at building this wheel, I added a quarter-turn
layer of tension, stress- relieved it all around, saw a very slight potato-
chip shape of maybe 2mm away from the centerline on either side
happening as I spun the wheel in the stand, backed it off a half turn on
both sides, all as per The Bicycle Wheel, and the result after the de-
tensioning was that it was about as true as it was prior to the last
additional tension layer. On the initial build, if after my
overtensioning I had just backed off the tension all around a bit more
instead of starting over, would the wheel have gone back to trueness,
presuming that all my nipple-turning had been accurate enough? Does it
depend on exactly how overloaded and deformed the rim became? In The
Book, it says that after you overload a rim during stress relieving,
some truing will be necessary after you back it off half a turn all
around. But none of the potato-chip shape from overloading is supposed
to be remaining at that point, right? If it was, and you trued the rim
in reaction to that, wouldn't everything just get really screwed up? So
is the truing you'll be needing to do at that point just in reaction to
inaccuracies in your nipple-turning? How exactly do all the rules about
all this apply to rims of different types and weights? When you stress
relieve a rim to test it for overload, are you supposed to be watching
the rim for a potato-chip shape happening as you squeeze each group of 4
spokes and then stop if you see one, or should you just go through and
stress relieve all the spokes and then check to see if the deformation
occured somewhere in the process?
There was another time when I stress relieved all around and then saw
that the rim was in a shape that resembled the slight potato
chip/saddle shape of an overloaded rim, but not quite. Whereas the
usual shape is a series of curves where there's an apex veering to the
left, followed by an apex veering to the right 90 degrees later, and an
apex to the left another 90 degrees from that, etc. this series of
curves went more like apex to the left followed by one to the right 45
degrees later, followed by the next one to the left 135 degrees later,
followed by one to the right 45 degrees later, etc, such that both
curves going to one side were still 180 degrees from each other, but
the overall shape was weird. Again, this was after I tensioned and
stress relieved the wheel. I figured that this was just a sign of
overload but am still not really sure if I'm missing something. Does
rim deformation just happen this way sometimes? Are there other
variations on the typical imploded- rim shape?
When stress relieving spokes, all internal stresses are relieved after
you make one complete round of squeezing adjacent spokes beyond yield,
right? If so, does that mean that if you were building up a rim that you
absolutely knew was strong enough that difficulty in turning nipples was
going to be the tension bottleneck for the wheel, you would only really
have to stress relieve once, when you hit the point where no more
tension can be added?
I'm also wondering about how exactly techniques to eliminate spoke
windup work. When you overshoot a quarter turn and then back up to
eliminate windup, is the idea that somewhere in that extra quarter turn,
the spoke's increasing torsional load will become enough to overcome the
amount of friction between its threads and those of the nipple? What
exactly keeps the spoke from winding up in the other direction when you
back up the nipple? When you go to back up the nipple, isn't there just
going to be more friction than you started with because now the spoke is
tighter by a quarter turn plus whatever adjustment you wanted to make?
Is it the best idea to keep one hand on the spoke you're adjusting as
the other turns the spoke wrench, so that you can feel when a spoke is
winding up and when it unwinds? Is it possible for a spoke to only
unwind partially?
I'm also wondering why hardly anything I've read about wheelbuilding
mentions the possibility of tightening drive
vs. non-drive-side spokes according to a ratio based on how much they
pull the rim due to their differing angles, and how much tension
each side will have in total when the wheel is done. The ratio is
something like 8:5 for most 9-speed rears, isn't it? So why not just
do your tensioning layers and truing adjustments by turning the
drive side something like twice as much all the way through? If you
just act like both sides pull the same amount and therefore you make
even increments on both sides when you're tensioning, dishing, or
truing, aren't you bound to create lateral/dish errors that must be
dealt with using the same flawed process? I was experimenting with
this and it seems like there may be something to it, but this time
around I was confused about enough things that throwing this in the
mix was more than I really wanted to deal with.
In The Bicycle Wheel, it's written that wheels with unbalanced spoke
tensions will equalize themselves in use. Is this just for the obvious
reason that the spokes with low tensions will get looser and out of true
in use, which causes all sorts of havoc, or is there something subtle
I'm missing here that causes problems when some spokes are also
inordinately high in tension, other than increasing the likelihood of
eyelet cracking? Does this imply, for example, that a wheel with
generally closely balanced, high tensions but a few spokes at
inordinately high tensions for some reason would all equalize in use?
A final group of questions has to do with interactions between radial
trueness, tension balancing, and rim imperfections. I got my wheel to a
point several times where the total tension difference between the
slackest and tightest drive-side spokes was about 30 KgF, with a few at
about 95, a few at about 125-130, and most at about 105-120, and a
similar bunch of disparities on the non-drive-side. This was at about
the max safe tension for the rim using the Jobst method unless I'm very
confused. There was still quite a bit of radial truing error, perhaps
1mm between high and low points, but it was arranged in the classic
annoying pattern where the bumps are tighter spots and the dips are
looser spots. In other words, if I just went through and made the
tension on each spoke exactly the same without regard to how true it
would make the wheel, then the wheel would be a total mess. I was left
with the definite feeling that I was just encountering imperfections in
the rim, since I worked on it for a long and it seemed like there was
little further I could do without compromising either tension balance or
reasonable trueness. On the other hand, I'm fairly new at this and I
don't want to put undue blame on the rim. My question is just how bad
are the tolerances on Sun rims, or CR-18s in particular for those who
have lots of experience with them, and what kind of tension disparities
do you usually end up with?
Thanks for reading and replying, Nate Knutson



Spoke alignment is key to having the wheel turn out to be durable. In
short, the shortest distance between two points is a straight line.
Take a thread and stretch it along the path of each spoke to see how
close the are to straight. This has nothing to do with tension itself,
but it does have to do with how spokes respond in dynamic loading and
unloading. When you work aligned spokes you get more equal response. I
agree with the other posters responses about the expected elasticity
of stainless spokes and even tension. I have had very good and very
bad experiences with Sun rims. I think some Sun rims come through with
very bad quality control. Peter White, of Peter White Cycles, has
mentioned this in his write up on wheels. I have tossed CR-18s in the
recycling bin due to this. It is very frusrating to go through an
entire rear build and arrive at that point. I am not suggesting that
you throw out your work, but I expect to get tension balance between 5
& 10% while having lateral and radial true better than 0.3mm. My
expectation is met on all wheels I send out and I have found some Sun
rims that will allow this. I have also found more than a few Sun rim
samples that wouldn't even come close. It is up to you and your pride
as to what you want to do next.



--

wrote in message ...

The spokes will not change but the rim will, assuming the wheel runs
over average bumpy roads that momentarily impart high stress to the
rim. Under these conditions, the rim will gradually conform to
tension distribution and thereby change individual preloads of the
spokes. The rim adapts and this alters spoke tension.

Jobst Brandt


What I was wondering about in my original post is whether your book is
stating that this works in the case of a radially true wheel that
happens to have some spokes at HIGHER tension than one would like,
rather than lower. I understand what happens when a spoke is too loose
- it gets completely unloaded in use, which causes the rim to exceed
yield and get deformed inwards there, causing the already-loose spoke
to be at even lower tension, causing the wheel to go out of true
laterally and also eventually causing its neighboring spokes to get
unloaded more in use, starting a cycle that basically destroys the rim
and equalizes tension while doing so.

But say I have a wheel whose rim is either low tolerance, damaged, or
defective, and to get it reasonably true radially, even to a standard
of like 1mm or so, I'm forced to raise tension in one area of the rim
somewhat past the margin one would prefer they use as a standard
acceptable amount of deviation for tension-balancing purposes. In
other words, say we have a wheel with 33 reasonably tension-balanced
spokes and a group of 3 adjacent ones where the middle spoke in the
group is 20-30 KgF's higher than the rest, but all the spokes in the
wheel are past the level of tension where you don't have to worry more
than usual about them getting completely unloaded in use. I know this
is a highly imperfect situation (albeit a plausible one) and I know
that the chances of rim cracking go up dramatically here - all I'm
wondering about is whether the book is saying that this situation will
also cause the wheel to somehow equalize in tension.

And while I'm thinking about it, a wheel is closest to failure due to
excess tension at the areas of the rim where spoke tension is the
highest, right? That is, say I was riding the aforementioned wheel
with a few spokes that are way tighter than the rest. The wheel gets
strongly side-loaded for some reason. Is it the case that if this side
load occurred when one of the spokes at average tension was contacting
the ground, the wheel might be fine, but if the lone excessively
tensioned spot was contacting the ground then the same load would
cause the wheel to overload and collapse? In other words, failure due
to tension overload happens because of the rim getting overloaded and
yielding in one specific place, as opposed to the total spoke tension
on the rim becoming too great, right? If this is the case, does that
mean that when one intentionally overloads groups of 4 spokes to check
how close the wheel is to maximum safe tension, what you're mostly
looking for is whether the rim will start collapsing in the spots
where the spoke tension is highest and/or where the rim is weakest,
like the valve hole?
Thanks,
Nate Knutson