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Tensiometer curiosity



 
 
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  #1  
Old March 31st 07, 02:28 PM posted to rec.bicycles.tech
richard
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Posts: 109
Default Tensiometer curiosity

Having yet to build my first wheel, I have a question about tensiometers.

Is the absolute measure of (whatever - isn't it really a distance
deflection rather than a force, although threads tend to indicate that
it reads in force) that critical? OR, is the only thing critical its
ability to give the same reading on the same spoke (and spokes with the
same tension) consistantly?

In other words, is "each spoke tightened to so many Kg" as important as
knowing all spokes are tensioned equally?
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  #2  
Old March 31st 07, 02:50 PM posted to rec.bicycles.tech
Ozark Bicycle
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Posts: 3,591
Default Tensiometer curiosity

On Mar 31, 7:28 am, richard wrote:
Having yet to build my first wheel, I have a question about tensiometers.

Is the absolute measure of (whatever - isn't it really a distance
deflection rather than a force, although threads tend to indicate that
it reads in force) that critical? OR, is the only thing critical its
ability to give the same reading on the same spoke (and spokes with the
same tension) consistantly?

In other words, is "each spoke tightened to so many Kg" as important as
knowing all spokes are tensioned equally?


IMO, knowing that spoke tension is consistent from spoke to spoke
(i.e., "relative" spoke tension) is more critical than knowing the
"absolute" spoke tension to a really great degree of accuracy (IOW,
95Kgf v. 105Kgf is not a big deal).




  #3  
Old March 31st 07, 03:27 PM posted to rec.bicycles.tech
Ben C
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Posts: 3,084
Default Tensiometer curiosity

On 2007-03-31, Ozark Bicycle wrote:
On Mar 31, 7:28 am, richard wrote:
Having yet to build my first wheel, I have a question about tensiometers.

Is the absolute measure of (whatever - isn't it really a distance
deflection rather than a force, although threads tend to indicate that
it reads in force) that critical? OR, is the only thing critical its
ability to give the same reading on the same spoke (and spokes with the
same tension) consistantly?

In other words, is "each spoke tightened to so many Kg" as important as
knowing all spokes are tensioned equally?


IMO, knowing that spoke tension is consistent from spoke to spoke
(i.e., "relative" spoke tension) is more critical than knowing the
"absolute" spoke tension to a really great degree of accuracy (IOW,
95Kgf v. 105Kgf is not a big deal).


This is something I've never understood. I don't bother with a
tensiometer myself, but surely if the spoke tensions aren't all about
the same then the wheel will be out of true? And if the only way to get
it true is with uneven tensions (if for example the rim isn't round and
flat in the first place), then you probably need uneven tension since
you will obviously require the wheel to be true.

I suppose if every other spoke on each side was loose you could have a
true wheel with uneven tension, but there's a minimal chance of that
happening by mistake.
  #4  
Old March 31st 07, 03:44 PM posted to rec.bicycles.tech
Ozark Bicycle
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Posts: 3,591
Default Tensiometer curiosity

On Mar 31, 8:27 am, Ben C wrote:
On 2007-03-31, Ozark Bicycle wrote:





On Mar 31, 7:28 am, richard wrote:
Having yet to build my first wheel, I have a question about tensiometers.


Is the absolute measure of (whatever - isn't it really a distance
deflection rather than a force, although threads tend to indicate that
it reads in force) that critical? OR, is the only thing critical its
ability to give the same reading on the same spoke (and spokes with the
same tension) consistantly?


In other words, is "each spoke tightened to so many Kg" as important as
knowing all spokes are tensioned equally?


IMO, knowing that spoke tension is consistent from spoke to spoke
(i.e., "relative" spoke tension) is more critical than knowing the
"absolute" spoke tension to a really great degree of accuracy (IOW,
95Kgf v. 105Kgf is not a big deal).


This is something I've never understood. I don't bother with a
tensiometer myself, but surely if the spoke tensions aren't all about
the same then the wheel will be out of true?


It ain't necessarily so.....


And if the only way to get
it true is with uneven tensions (if for example the rim isn't round and
flat in the first place), then you probably need uneven tension since
you will obviously require the wheel to be true.



That is a slightly different situation, but even then, having a
balance between true/round and even/balanced tension is the best
compromise.



I suppose if every other spoke on each side was loose you could have a
true wheel with uneven tension, but there's a minimal chance of that
happening by mistake.


I guess that depends on your definition of "loose". If by "loose" you
mean the tension is too low, that is not uncommon. Too high on some
spokes, too low on others; it happens all the time.

  #5  
Old March 31st 07, 04:56 PM posted to rec.bicycles.tech
jim beam
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Posts: 5,758
Default Tensiometer curiosity

richard wrote:
Having yet to build my first wheel, I have a question about tensiometers.

Is the absolute measure of (whatever - isn't it really a distance
deflection rather than a force, although threads tend to indicate that
it reads in force) that critical? OR, is the only thing critical its
ability to give the same reading on the same spoke (and spokes with the
same tension) consistantly?

In other words, is "each spoke tightened to so many Kg" as important as
knowing all spokes are tensioned equally?


relatively consistent tension is critical for a true wheel that stays
true in service. however, the absolute tension is essential if you want
to have a rim that doesn't crack or have eyelets that don't pull out.
what most people do therefore is measure 3 or so spokes and average
their absolute readings, then go around the wheel making sure other
spokes have the same pitch when plucked. you'll never get all spokes
identical because all rims are slightly inconsistent, but aim for the
closest you can get. [spokes at the rim joint are often over-tension,
so exclude them from your average.]
  #6  
Old March 31st 07, 05:03 PM posted to rec.bicycles.tech
Antti Salonen
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Posts: 60
Default Tensiometer curiosity

Ben C wrote:

This is something I've never understood. I don't bother with a
tensiometer myself, but surely if the spoke tensions aren't all about
the same then the wheel will be out of true?


This depends a lot on the rim and the spoke count. If you use a strong,
stiff rim with 32 or 36 spokes, for example a typical MTB wheel, you can
have one spoke a lot looser than the others without the wheel being out
of true - As long as the adjacent spokes are very tight.

On the other hand, if you build a front wheel with a lightweight road
rim and only 24 or 28 spokes what you say is closer to truth.

-as
  #7  
Old March 31st 07, 05:16 PM posted to rec.bicycles.tech
Tim McNamara
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Posts: 6,945
Default Tensiometer curiosity

In article ,
Ben C wrote:

On 2007-03-31, Ozark Bicycle
wrote:
On Mar 31, 7:28 am, richard wrote:
Having yet to build my first wheel, I have a question about
tensiometers.

Is the absolute measure of (whatever - isn't it really a distance
deflection rather than a force, although threads tend to indicate
that it reads in force) that critical? OR, is the only thing
critical its ability to give the same reading on the same spoke
(and spokes with the same tension) consistantly?

In other words, is "each spoke tightened to so many Kg" as
important as knowing all spokes are tensioned equally?


IMO, knowing that spoke tension is consistent from spoke to spoke
(i.e., "relative" spoke tension) is more critical than knowing the
"absolute" spoke tension to a really great degree of accuracy (IOW,
95Kgf v. 105Kgf is not a big deal).


Well, most tensiometers don't give you a flawless absolute measurement
for reasons that have been discussed in other threads. They do give you
a ballpark measurement that is IMHO close enough to be getting on with.
There are techniques for finding the highest tension the rim can
withstand to maximize the load the wheel can carry, but most people
probably don't need to have their wheels quite that tight since they
don't load the wheel that heavily.

This is something I've never understood. I don't bother with a
tensiometer myself, but surely if the spoke tensions aren't all about
the same then the wheel will be out of true? And if the only way to
get it true is with uneven tensions (if for example the rim isn't
round and flat in the first place), then you probably need uneven
tension since you will obviously require the wheel to be true.


Take wheels at random and pluck them and you will often find that there
are some spokes that are much tighter than others. That's because the
lateral pull of spokes affects not on the part of the rim the spokes are
connected to but also a few inches to either side. This is because of
the lateral rigidity of the rim. This scenario can potentially result
in the looser spoke going slack under load and the nipple backing off,
which can eventually put the wheel out of true.
  #8  
Old March 31st 07, 05:55 PM posted to rec.bicycles.tech
Ron Ruff
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Posts: 1,304
Default Tensiometer curiosity

On Mar 31, 6:28 am, richard wrote:
In other words, is "each spoke tightened to so many Kg" as important as
knowing all spokes are tensioned equally?


As others have said you can pluck the spokes to get relative tension
even on each side, but a tensiometer is necessary (for me at least) to
get the absolute tension correct. Generally, you want the tension as
high as the rim spec (or until buckling occurs), but if tension is
much lower than this, then the spokes might go slack in service which
reduces the strength of the wheel, and may also result in loosening
(if they aren't locktited), and early fatigue. The spoke wrench is the
only tool you really need to build a wheel, but I'd say that a
tensiometer is the 2nd most important. At least it is a good idea to
check your spoke tension at a local shop if you don't want to buy
one.

It is very easy to get a wheel acceptably true, but still have
tensions varying all over the place. Basically, the rim stiffness is
enough to mask the variation. Sloppy building jobs are like this...
including cheap machine built wheels I've had.


  #9  
Old March 31st 07, 06:03 PM posted to rec.bicycles.tech
Ben C
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Posts: 3,084
Default Tensiometer curiosity

On 2007-03-31, Tim McNamara wrote:
In article ,
Ben C wrote:

[...]
This is something I've never understood. I don't bother with a
tensiometer myself, but surely if the spoke tensions aren't all about
the same then the wheel will be out of true? And if the only way to
get it true is with uneven tensions (if for example the rim isn't
round and flat in the first place), then you probably need uneven
tension since you will obviously require the wheel to be true.


Take wheels at random and pluck them and you will often find that there
are some spokes that are much tighter than others. That's because the
lateral pull of spokes affects not on the part of the rim the spokes are
connected to but also a few inches to either side.


So you could end up with, for example, one spoke that was too tight with
the two either side of it on that side of the rim a bit loose, and still
have a fairly true wheel since the rim's rigidity will not permit a
wobble that small. This is especially possible with 36H and a rigid rim
which is what Antti also said.

This is because of the lateral rigidity of the rim. This scenario can
potentially result in the looser spoke going slack under load and the
nipple backing off, which can eventually put the wheel out of true.


Which I suppose is the basic reason why even tension is desirable.
  #10  
Old March 31st 07, 06:17 PM posted to rec.bicycles.tech
Ozark Bicycle
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Posts: 3,591
Default Tensiometer curiosity

On Mar 31, 10:55 am, "Ron Ruff" wrote:
On Mar 31, 6:28 am, richard wrote:

In other words, is "each spoke tightened to so many Kg" as important as
knowing all spokes are tensioned equally?


As others have said you can pluck the spokes to get relative tension
even on each side


It can be quite illuminating to set even tension by "plucking" and
then go around the wheel spoke by spoke and see how even the tension
truly is.




 




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