Tensiometer curiosity

[richard]

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?

 

[Ozark Bicycle]

On Mar 31, 7:28 am, richard <[email protected]> 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).

 

[Ben C]

On 2007-03-31, Ozark Bicycle <[email protected]> wrote:
> On Mar 31, 7:28 am, richard <[email protected]> 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.

 

[Ozark Bicycle]

On Mar 31, 8:27 am, Ben C <[email protected]> wrote:
> On 2007-03-31, Ozark Bicycle <[email protected]> wrote:
>
>
>
>
>
> > On Mar 31, 7:28 am, richard <[email protected]> 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.

 

[jim beam]

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.]

 

[Antti Salonen]

Ben C <[email protected]> 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

 

[Tim McNamara]

In article <[email protected]>,
Ben C <[email protected]> wrote:

> On 2007-03-31, Ozark Bicycle <[email protected]>
> wrote:
> > On Mar 31, 7:28 am, richard <[email protected]> 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.

 

[Ron Ruff]

On Mar 31, 6:28 am, richard <[email protected]> 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.

 

[Ben C]

On 2007-03-31, Tim McNamara <[email protected]> wrote:
> In article <[email protected]>,
> Ben C <[email protected]> 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.

 

[Ozark Bicycle]

On Mar 31, 10:55 am, "Ron Ruff" <[email protected]> wrote:
> On Mar 31, 6:28 am, richard <[email protected]> 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.

 

[[email protected]]

Ozark writes:

>>> 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.

Other than measurement anomalies such as stiction or a wavy spoke, the
readings will be identical as the observer's ear to detect tone. For
this reason a tensiometer should have a zero-on-the-fly capability to
correct for slight waves in spokes. Of course if the test load is as
great as the Hozan, that doesn't make much difference.

Jobst Brandt

 

[jim beam]

[email protected] wrote:
> On Sat, 31 Mar 2007 08:56:12 -0700, jim beam
> <[email protected]> wrote:
>
> [snip]
>
>> [spokes at the rim joint are often over-tension . . .
>
> Dear Jim,
>
> There seems to be some disagreement about whether spokes at the rim
> joint end up tighter or looser.
>
> Perhaps "over-tension" was just the kind of obvious oops that we all
> make now and then, and you meant "under-tension"?
>
> (Aaargh! Smack forehead! Never mind!)
>
> But perhaps you really do expect spokes at the rim joint to be
> tighter?
>
> Anyway, here's the usual thinking on spokes at the rim joint:
>
> "Note that some rims require spokes adjacent to the joint to be looser
> than others to correct for their greater thickness at the splice."
>
> "The Bicycle Wheel," 3rd edition, p. 95
>
> "Most rims are made from straight material that is formed into a hoop
> and joined by welding or splicing. Sometimes the joint causes
> irregular alignment that is difficult to correct. For spliced rims,
> the extent of the error may not appear until after the spokes are
> tensioned. In both welded and spliced rims spokes near the joint may
> be looser than others, and completely correcting this error may be
> impossible."
>
> "The Bicycle Wheel," 3rd edition, p. 104
>
> Cheers,
>
> Carl Fogel

maybe it's because jobst never builds with welded rims. /my/ experience
is that welded rims need over-tension. and i would expect that if
excess weld material makes that section more rigid.

http://flickr.com/photos/38636024@N00/275085692/

 

[[email protected]]

On Sat, 31 Mar 2007 08:56:12 -0700, jim beam
<[email protected]> wrote:

[snip]

>[spokes at the rim joint are often over-tension . . .

Dear Jim,

There seems to be some disagreement about whether spokes at the rim
joint end up tighter or looser.

Perhaps "over-tension" was just the kind of obvious oops that we all
make now and then, and you meant "under-tension"?

(Aaargh! Smack forehead! Never mind!)

But perhaps you really do expect spokes at the rim joint to be
tighter?

Anyway, here's the usual thinking on spokes at the rim joint:

"Note that some rims require spokes adjacent to the joint to be looser
than others to correct for their greater thickness at the splice."

"The Bicycle Wheel," 3rd edition, p. 95

"Most rims are made from straight material that is formed into a hoop
and joined by welding or splicing. Sometimes the joint causes
irregular alignment that is difficult to correct. For spliced rims,
the extent of the error may not appear until after the spokes are
tensioned. In both welded and spliced rims spokes near the joint may
be looser than others, and completely correcting this error may be
impossible."

"The Bicycle Wheel," 3rd edition, p. 104

Cheers,

Carl Fogel

 

[Ron Ruff]

On Mar 31, 11:23 am, jim beam <[email protected]> wrote:
> maybe it's because jobst never builds with welded rims. /my/ experience
> is that welded rims need over-tension. and i would expect that if
> excess weld material makes that section more rigid.

The change in curvature between a built and unbuilt wheel is going to
be very small, though. I'd wager that it depends on how the rim was
distorted when the joint was put in... could go either way.

 

[Ozark Bicycle]

On Mar 31, 11:34 am, [email protected] wrote:
> Ozark writes:
> >>> 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.
>
> Other than measurement anomalies such as stiction or a wavy spoke, the
> readings will be identical as the observer's ear to detect tone.


Which, of course, can vary with mood, time of day, ambient noise,
distractions, etc.

Why not just use the tensiometer?

 

[Ben C]

On 2007-03-31, jim beam <[email protected]> wrote:
> [email protected] wrote:
[...]
>> Dear Jim,
>>
>> There seems to be some disagreement about whether spokes at the rim
>> joint end up tighter or looser.
[...]
>> Anyway, here's the usual thinking on spokes at the rim joint:
>>
>> "Note that some rims require spokes adjacent to the joint to be looser
>> than others to correct for their greater thickness at the splice."
[...]
> maybe it's because jobst never builds with welded rims. /my/ experience
> is that welded rims need over-tension. and i would expect that if
> excess weld material makes that section more rigid.
>
> http://flickr.com/photos/38636024@N00/275085692/

I've noticed a very small flat-spot on modern Mavic rims (CXP-23) around
the weld. Or around the join, I assume they were welded.

Normally to correct a flat spot you'd loosen the spokes a bit under the
flat spot. If that section is more rigid I suppose you'd just need an
even bigger difference in tension.

If the rim was round initially but stiffer at the weld, then you might
expect a high spot there after building which you'd correct by
increasing the tension around the weld.

So there might be two factors here-- first the weld making the rim
stiffer at that point, and second, the presence of the weld making the
rim a bit flattened at that point for some other reason, which might
just be random on particular rims.

 

[Tim McNamara]

In article <[email protected]>,
jim beam <[email protected]> wrote:

> /my/ experience is that welded rims need over-tension. and i would
> expect that if excess weld material makes that section more rigid.

I've seen both conditions. The joint is, as you say, stiffer than the
rest of the rim if it's sleeved inside the weld which makes compensating
for the concentric error result in exaggerated differences in spoke
tension.

In some wheels the spokes at the rim joint- whether welded, pinned,
whatever, makes no difference- have higher tension than the rest of the
spokes, and in some wheels they have lower tension. I've also built
wheels in which the spoke tension at the joint was the same as the rest
of the spokes. It depends on which way the concentric error at the
joint, if any, goes. If the joint is a high spot, spoke tension will be
higher; if the joint is a low spot joint tension will be lower.

 

[Tim McNamara]

In article <[email protected]>,
Ben C <[email protected]> wrote:

> On 2007-03-31, Tim McNamara <[email protected]> wrote:
> > In article <[email protected]>,
> > Ben C <[email protected]> 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.

Even rims that aren't particularly rigid. I saw this back in the days
of simple U-channel rims, before box section rims were common. The
reverse scenario is also possible. You can often find a loose spoke in
a wheel that is compensated for by its adjacent same-side spokes being
tensioned a bit tighter, making the wheel laterally true.

We use this to our advantage when we break a spoke and adjust the
same-side spokes on either side of the gap to reduce the wow in the rim
to ride home.

> > 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.

A vertically stiffer rim might even magnify the issue, since the wheel
stands on fewer spokes in the load-affected zone. That one loose spoke
would lose more tension as a result.

 

[Tim McNamara]

In article <[email protected]>,
"Ron Ruff" <[email protected]> wrote:

> 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.

That's a good description.

 

[Ron Ruff]

On Mar 31, 4:18 pm, Tim McNamara <[email protected]> wrote:
> A vertically stiffer rim might even magnify the issue, since the wheel
> stands on fewer spokes in the load-affected zone. That one loose spoke
> would lose more tension as a result.

I think you have it backwards on that one. The stiffer rim will
increase the dimensions of the load effected zone (all else being
equal), resulting in less of a tension change.