C
On Sat, 17 Mar 2007 16:46:41 -0500, Ben C <[email protected]> wrote:
>On 2007-03-17, [email protected] <[email protected]> wrote:
>> On 17 Mar 2007 20:04:39 GMT, [email protected] wrote:
>>
>>>Carl Fogel writes:
>[...]
>>>> Squeezing spoke pairs together usually changes something enough to
>>>> require small truing adjustments:
>>>
>>>> "If, after stress relieving, the wheel is appreciably out of true in
>>>> two smooth waves, then tension was too high, and retruing should
>>>> begin by relaxing tension of all spokes half a turn. Usually, only
>>>> small lateral corrections will be necessary after stress relieving."
>>>
>>>> --"The Bicycle Wheel," 3rd edition, p. 106
>>>
>>>I find that is a misinterpretation. The above citation explains what
>>>occurs if spoke tension it too high, not what stress relieving does.
>>>The issue at hand is whether spokes must be re-tensioned after stress
>>>relieving. The above mentions retruing, not re-tensioning. Spokes do
>>>not require re-tensioning!
>[...]
>> Dear Jobst,
>>
>> "Usually, only small lateral corrections will be necessary after
>> stress relieving."
>>
>> What is the difference between turning a spoke nipple to laterally
>> true a rim and turning a spoke nipple to change the spoke tension?
>
>The difference is in the intention. In one case you adjust one or two
>spokes to make the wheel true; in the other you adjust them all to
>change the wheel's tension.
>
>We still make distinctions between radial truing, lateral truing,
>tensioning and dishing, even though they all consist of turning the
>nipples.
>
>(Conversely, bashing the wheel on a tree-trunk, walking on it, squeezing
>it, leaning on it and mangling it with a crowbar are all called the same
>thing: "stress-relief").
>
>If stress-relief reduced whole-spoke tension significantly you'd expect
>to have to tighten up all the spokes by a bit to compensate, since you
>have stress-relieved all of them. That it may affect the tension of one
>or two enough to require a bit of re-truing just reflects the fact that
>nothing's perfect.
Dear Ben,
Why do sections of the rim move laterally enough to need truing after
spoke pairs are squeezed?
I can think of four possible reasons, any or all of which may be
involved.
First, the rim may not actually change. It could be that the wheel
builder tensions and trues the wheel up, squeezes all the spoke pairs,
gives the wheel a spin, and just can't help himself--the wheel hasn't
actually changed, but it can always be trued a little here or there.
This would be perfectly understandable, nothing dishonest.
(For all I know, the lateral movement is so gross and obvious to
experienced wheel builders that this psychological explanation can be
dismissed. I haven't enough confidence in my truing and tensioning to
have an opinion one way or the other.)
Second, some piece of metal may actually change. The rim, socket,
eyelet, nipple, spoke, or hub could yield here or there, which would
cause the rim to need some lateral truing.
(That's the point that I think is being debated here.)
Third, the rim may be able to move laterally without any metal
yielding on a cross-X laced wheel. When spoke pairs are squeezed,
there may be no noticeable yielding of the kind that would let the rim
move from side to side--but the crossings could shift slightly to a
new position, adding or reducing tension.
If two spokes were stuck at the crossing and squeezing them unstuck
them, then their tension would be slightly reduced and the rim would
move away from their side of the hub.
(No yielding is involved here, just the stubborn friction of crossed
spokes. But the overall tension changes.)
Fourth, the tension of all the spokes and the rim might somehow be
re-arranged without changing the sum. Nothing yields, the total
tension doesn't change, but the rim changes shape--this section bends
a little to one side, but another section bends exactly enough to the
other side to compensate.
(I think that's what you're suggesting, but I may be wrong.)
Cheers,
Carl Fogel
>On 2007-03-17, [email protected] <[email protected]> wrote:
>> On 17 Mar 2007 20:04:39 GMT, [email protected] wrote:
>>
>>>Carl Fogel writes:
>[...]
>>>> Squeezing spoke pairs together usually changes something enough to
>>>> require small truing adjustments:
>>>
>>>> "If, after stress relieving, the wheel is appreciably out of true in
>>>> two smooth waves, then tension was too high, and retruing should
>>>> begin by relaxing tension of all spokes half a turn. Usually, only
>>>> small lateral corrections will be necessary after stress relieving."
>>>
>>>> --"The Bicycle Wheel," 3rd edition, p. 106
>>>
>>>I find that is a misinterpretation. The above citation explains what
>>>occurs if spoke tension it too high, not what stress relieving does.
>>>The issue at hand is whether spokes must be re-tensioned after stress
>>>relieving. The above mentions retruing, not re-tensioning. Spokes do
>>>not require re-tensioning!
>[...]
>> Dear Jobst,
>>
>> "Usually, only small lateral corrections will be necessary after
>> stress relieving."
>>
>> What is the difference between turning a spoke nipple to laterally
>> true a rim and turning a spoke nipple to change the spoke tension?
>
>The difference is in the intention. In one case you adjust one or two
>spokes to make the wheel true; in the other you adjust them all to
>change the wheel's tension.
>
>We still make distinctions between radial truing, lateral truing,
>tensioning and dishing, even though they all consist of turning the
>nipples.
>
>(Conversely, bashing the wheel on a tree-trunk, walking on it, squeezing
>it, leaning on it and mangling it with a crowbar are all called the same
>thing: "stress-relief").
>
>If stress-relief reduced whole-spoke tension significantly you'd expect
>to have to tighten up all the spokes by a bit to compensate, since you
>have stress-relieved all of them. That it may affect the tension of one
>or two enough to require a bit of re-truing just reflects the fact that
>nothing's perfect.
Dear Ben,
Why do sections of the rim move laterally enough to need truing after
spoke pairs are squeezed?
I can think of four possible reasons, any or all of which may be
involved.
First, the rim may not actually change. It could be that the wheel
builder tensions and trues the wheel up, squeezes all the spoke pairs,
gives the wheel a spin, and just can't help himself--the wheel hasn't
actually changed, but it can always be trued a little here or there.
This would be perfectly understandable, nothing dishonest.
(For all I know, the lateral movement is so gross and obvious to
experienced wheel builders that this psychological explanation can be
dismissed. I haven't enough confidence in my truing and tensioning to
have an opinion one way or the other.)
Second, some piece of metal may actually change. The rim, socket,
eyelet, nipple, spoke, or hub could yield here or there, which would
cause the rim to need some lateral truing.
(That's the point that I think is being debated here.)
Third, the rim may be able to move laterally without any metal
yielding on a cross-X laced wheel. When spoke pairs are squeezed,
there may be no noticeable yielding of the kind that would let the rim
move from side to side--but the crossings could shift slightly to a
new position, adding or reducing tension.
If two spokes were stuck at the crossing and squeezing them unstuck
them, then their tension would be slightly reduced and the rim would
move away from their side of the hub.
(No yielding is involved here, just the stubborn friction of crossed
spokes. But the overall tension changes.)
Fourth, the tension of all the spokes and the rim might somehow be
re-arranged without changing the sum. Nothing yields, the total
tension doesn't change, but the rim changes shape--this section bends
a little to one side, but another section bends exactly enough to the
other side to compensate.
(I think that's what you're suggesting, but I may be wrong.)
Cheers,
Carl Fogel