"Sheldon Brown" <[email protected]
> wrote in message
> 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.
> >>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?
> > 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