Park spoke tensiometer

[John Davies]

Does anyone have any comments on the new TM-1 Spoke Tension Meter?

http://www.parktool.com/tools/TM_1.shtml

I have seen it for US$49. Any cheaper sources?

TIA.

John Davies Monroe WA USA

2001 Saab 9-5 Aero Wagon 2000 Audi A4 quattro 1.8T 1991 Jeep Cherokee Laredo 4x4

 

[Jobst Brandt]

John Davies writes:

> Does anyone have any comments on the new TM-1 Spoke Tension Meter?

These guys have a problem even with the name of the tool that is a tensiometer, quite aside from the
shortcomings in design. It measures across the thickness of the spoke so spoke thickness enters into
the reading, uses a high force that it must because it has low resolution and it cannot be checked
for a null reading, that is it cannot be zeroed for the measurement. High test force adds tension to
the spoke and falsifies actual tension, especially for looser spokes.

http://www.parktool.com/tools/TM_1.shtml

> I have seen it for US$49. Any cheaper sources?

It's better than no tensiometer at all. I don't know that the same instrument is available from
other sources.

Jobst Brandt [email protected] Palo Alto CA

 

[Kenny Lee]

John Davies wrote:
> Does anyone have any comments on the new TM-1 Spoke Tension Meter?
>
> http://www.parktool.com/tools/TM_1.shtml
>
> I have seen it for US$49. Any cheaper sources?
>
> TIA.
>
>
> John Davies Monroe WA USA
>
> 2001 Saab 9-5 Aero Wagon 2000 Audi A4 quattro 1.8T 1991 Jeep Cherokee Laredo 4x4
>
If you "have" Kung-fu, you can squeeze the spokes using your hands and come up with very
accurate readings.

Kenny Lee

 

[Sheldon Brown]

John Davies asked:
>
>>Does anyone have any comments on the new TM-1 Spoke Tension Meter?

Jobst Brandt replied:

> These guys have a problem even with the name of the tool that is a tensiometer,

That doesn't bother me as much as the mis-spelling of "laser" on their wrenches and literature. I
guess they think the acronym stands for "Light Amplification by Ztimulated Emission of Radiation"

> quite aside from the shortcomings in design. It measures across the thickness of the spoke so
> spoke thickness enters into the reading,

I believe that's true of all commercially available tensiometers.

> uses a high force that it must because it has low resolution and it cannot be checked for a null
> reading, that is it cannot be zeroed for the measurement. High test force adds tension to the
> spoke and falsifies actual tension, especially for looser spokes.

I don't see why this would be so. Why would the calibration chart not be accurate?

Sheldon "I Like It" Brown +---------------------------------------------------+
| The important thing is not to stop questioning. | Curiosity has its own reason for existing. |
| --Albert Einstein |
+---------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

 

[Gary Smiley]

I don't know if I have Kung-fu (I do have perfect pitch), but the last wheel I built (my fifth) just
felt right when I grabbed and squeezed the spokes. And it sounded right when I plunked all the
spokes. I've had it for a year, put around 3000 miles on it (including a tour in Europe), and I've
never had to adjust it- it's still as true as the day it was built.

Kenny Lee wrote:

>
> If you "have" Kung-fu, you can squeeze the spokes using your hands and come up with very accurate
> readings.
>
> Kenny Lee

 

[Jobst Brandt]

Sheldon Brown writes:

>>> Does anyone have any comments on the new TM-1 Spoke Tension Meter?

>> These guys have a problem even with the name of the tool that is a tensiometer,

> That doesn't bother me as much as the mis-spelling of "laser" on their wrenches and literature. I
> guess they think the acronym stands for "Light Amplification by Ztimulated Emission of Radiation"

>> quite aside from the shortcomings in design. It measures across the thickness of the spoke so
>> spoke thickness enters into the reading,

> I believe that's true of all commercially available tensiometers.

The Avocet/DT tensiometer depicted in "the Bicycle Wheel" does not measure across the spoke
thickness. That is why I designed it. There is no other instrument that meets the
requirements today.

>> uses a high force that it must because it has low resolution and it cannot be checked for a null
>> reading, that is it cannot be zeroed for the measurement. High test force adds tension to the
>> spoke and falsifies actual tension, especially for looser spokes.

> I don't see why this would be so. Why would the calibration chart not be accurate?

For a demonstration of this, try a Hozan tensiometer on a short spoke that is not tensioned in a
stiff rim. It will show adequate tension with this instrument. The Hozan is probably the worst of
these but it demonstrates the problem the best. I am reminded of Heisenberg's Uncertainty Principal
in this regard. In an effort to get a substantial reading, the tension to be measured is
compromised.

http://www.aip.org/history/heisenberg/ http://www.aip.org/history/heisenberg/p08.htm

I suppose a guitar string pulled to one side to sense its tension is also an example. If you pull it
sufficiently far, it will require practically the same force independent of initial tension.

Jobst Brandt [email protected] Palo Alto CA

 

[Huw Pritchard]

On Sat, 01 Mar 2003 04:33:06 +0000, Sheldon Brown did issue forth:

> That doesn't bother me as much as the mis-spelling of "laser" on their wrenches and literature. I
> guess they think the acronym stands for "Light Amplification by Ztimulated Emission of Radiation"

I think you have to admit that 'Ztimulated' is a much better word though.

--
Huw Pritchard Replace bounce with huw to reply by mail

 

[Kenny Lee]

Gary Smiley wrote:
> I don't know if I have Kung-fu (I do have perfect pitch), but the last wheel I built (my fifth)
> just felt right when I grabbed and squeezed the spokes. And it sounded right when I plunked all
> the spokes. I've had it for a year, put around 3000 miles on it (including a tour in Europe), and
> I've never had to adjust it- it's still as true as the day it was built.
>

If you 'know' you have 'perfect' pitch without the use of man made measuring instruments telling you
so, then that qualifies as 'having' Kung-fu.

Kenny Lee

 

[Sheldon Brown]

Jobst complained of the Park Tensiometer:

>>>quite aside from the shortcomings in design. It measures across the thickness of the spoke so
>>>spoke thickness enters into the reading,

I observed:

>>I believe that's true of all commercially available tensiometers.

Jobst wrote:

> The Avocet/DT tensiometer depicted in "the Bicycle Wheel" does not measure across the spoke
> thickness. That is why I designed it. There is no other instrument that meets the
> requirements today.

I knew that, but since that is not in existence as a commercial product, and no other tensiometer
has this feature, it is unfair to single out the Park unit for this, since every other tensiometer
you can buy works the same way.

>>>uses a high force that it must because it has low resolution and it cannot be checked for a null
>>>reading, that is it cannot be zeroed for the measurement. High test force adds tension to the
>>>spoke and falsifies actual tension, especially for looser spokes.

Moi:

>>I don't see why this would be so. Why would the calibration chart not be accurate?

I'll add: why would it be useful to measure tension on loose spokes?

Jobst:

> For a demonstration of this, try a Hozan tensiometer on a short spoke that is not tensioned in a
> stiff rim. It will show adequate tension with this instrument. The Hozan is probably the worst of
> these but it demonstrates the problem the best. I am reminded of Heisenberg's Uncertainty
> Principal in this regard. In an effort to get a substantial reading, the tension to be measured is
> compromised.

It would seem to me that this would have been taken into account, for spoke lengths in the normal
range, when the calibration table was generated.

There is also an advantage to the stronger spring--it reduces the effect of friction in the pivot on
the reading.

Sheldon "I Still Like It" Brown +--------------------------------+
| One does not win at chess by | seizing every opportune pawn | -- Michael Flynn |
+--------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-9772 FAX
617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide http://captainbike.com
http://sheldonbrown.com

 

[Jobst Brandt]

Sheldon Brown writes:

>>> I don't see why this would be so. Why would the calibration chart not be accurate?

> I'll add: why would it be useful to measure tension on loose spokes?

I took a loose spoke as an example to show how great the disparity between measurement and fact can
be. It's not that you should measure a truly loose spoke but that a spoke without sufficient tension
can appear to have the desired tension when measured with a large deflection force.

>> For a demonstration of this, try a Hozan tensiometer on a short spoke that is not tensioned in a
>> stiff rim. It will show adequate tension with this instrument. The Hozan is probably the worst of
>> these but it demonstrates the problem the best. I am reminded of Heisenberg's Uncertainty
>> Principal in this regard. In an effort to get a substantial reading, the tension to be measured
>> is compromised.

> It would seem to me that this would have been taken into account, for spoke lengths in the normal
> range, when the calibration table was generated.

Well it isn't and it cannot be because the environment in which a taught spoke resides cannot be
captured in a calibration chart. There are too many variables. The proper thing to do is to use a
light test load and a precision gauge. Listening to the tone of a plucked (free standing) spoke
comes closest because the excursions of the vibrating wire can be as little as a tenth of a
millimeter and still be audible.

> There is also an advantage to the stronger spring--it reduces the effect of friction in the pivot
> on the reading.

Not if it tensions the spoke, as it in fact does. That is why I cited Heisenberg who shows that in
the pursuit of measuring the atom the information is destroyed if you try too hard.

Jobst Brandt [email protected] Palo Alto CA

 

[David Ornee]

"Sheldon Brown" <[email protected]> wrote in message
news:[email protected]...
> Jobst complained of the Park Tensiometer:
>
> >>>quite aside from the shortcomings in design. It measures across the thickness of the spoke so
> >>>spoke thickness enters into the reading,
>
> I observed:
>
> >>I believe that's true of all commercially available tensiometers.
>
> Jobst wrote:
>
> > The Avocet/DT tensiometer depicted in "the Bicycle Wheel" does not measure across the spoke
> > thickness. That is why I designed it. There is no other instrument that meets the requirements
> > today.
>
> I knew that, but since that is not in existence as a commercial product, and no other tensiometer
> has this feature, it is unfair to single out the Park unit for this, since every other tensiometer
> you can buy works the same way.
>
> >>>uses a high force that it must because it has low resolution and it cannot be checked for a
> >>>null reading, that is it cannot be zeroed for the measurement. High test force adds tension to
> >>>the spoke and falsifies actual tension, especially for looser spokes.
>
> Moi:
>
> >>I don't see why this would be so. Why would the calibration chart not be accurate?
>
> I'll add: why would it be useful to measure tension on loose spokes?
>
> Jobst:
>
> > For a demonstration of this, try a Hozan tensiometer on a short spoke that is not tensioned in a
> > stiff rim. It will show adequate tension with this instrument. The Hozan is probably the worst
> > of these but it demonstrates the problem the best. I am reminded of Heisenberg's Uncertainty
> > Principal in this regard. In an effort to get a substantial reading, the tension to be measured
> > is compromised.
>
> It would seem to me that this would have been taken into account, for spoke lengths in the normal
> range, when the calibration table was generated.
>
> There is also an advantage to the stronger spring--it reduces the effect

> of friction in the pivot on the reading.
>
> Sheldon "I Still Like It" Brown

I agree with Sheldon's pragmatic approach on this one. If I didn't already own the Wheelsmith
Tensiometer I would purchase the Park. I think both are practical in actual applications. Proper
tension is determined by the responses of the rim involved. Tension balancing is what I use the
tensiometer for. It looks like the Park tool would be easier to handle than the Wheelsmith device.
Since I often go around the wheel 3 - 4 times with the device, ease of use makes a difference when
the operation is repeated over 100 times per wheel. If the measurements are repeatable and provide
sufficient resolution, that makes the device quite useful to me. If the relative accuracy allows me
to attain spoke tension balance within 10 kgf, I am satisfied. Disclaimers: I haven't seen the new
Park Tesiometer in person, but I have seen the advertisements. I don't have any business
relationships with Park, Wheelsmith, Sheldon Brown, or Jobst Brandt. I respect their contributions
to bicycling and understanding the bicycle. I use the principles in Jobst Brandt's book with every
wheel I build.

David Ornee, Western Springs, IL

 

[Benjamin Weiner]

[email protected] wrote:

> For a demonstration of this, try a Hozan tensiometer on a short spoke that is not tensioned in a
> stiff rim. It will show adequate tension with this instrument. The Hozan is probably the worst of
> these but it demonstrates the problem the best. I am reminded of Heisenberg's Uncertainty
> Principal in this regard. In an effort to get a substantial reading, the tension to be measured is
> compromised.

> http://www.aip.org/history/heisenberg/ http://www.aip.org/history/heisenberg/p08.htm

> I suppose a guitar string pulled to one side to sense its tension is also an example. If you pull
> it sufficiently far, it will require practically the same force independent of initial tension.

I think a good analogy for test equipment, better than Heisenberg, would be how the input impedance
of a voltmeter can affect the measurement if it is too low. For example if you have a 2000 ohms/volt
VM and you measure a source with 10 volts and internal impedance 20000 ohms, you won't get a reading
of 10 volts. OTOH if the VM has input 2Mega-ohms/volt, you will get the correct measurement.

I bring this up because, as you know, it's an entirely classical phenomenon. Analogies to the
Uncertainty Principle are dangerous - when teaching physics, you learn that people overinterpret
analogies, or take them too literally.