Qui si parla Campagnolo said:Artoi writes-Is the tone produced by plucking a spoke an important
gauge of even
tension on the wheel?
After a long ride over the weekend with a new trial set of wheels, I
noticed one spoke that sounded particularly dull when compared with
others. Is this a good sign that something has loosened? Could the tone
produced by plucking spokes be used as a good monitor on the condition
of the wheel?
Any comments? I'm thinking of taking it back to the store and have it
checked out.
Not unless you have a properly tensioned wheel/spoke for
comparison(determined by a tensionometer), in the same gauge and also
have great music pitch ability. Generally it's a poor way to do things.
A tensionometer or Jobst's method in his book work MUCH better, are
more accurate.
Dear Peter,
First, congratulations on that extra "o" in "tensionometer"!
Usually we just use an extra "n" when we goad poor Jobst with
"tensionmeter" to provoke his "tensiometer" reply.
A truly cruel version would use hyphens to emphasize your new
spelling. For example, Cletus from the Simpsons might express his
admiration thus: "Brandine, I really like this here Joe-Bob Brandt
Tension-O-Meter what WalMart sells."
Linguistic quibbles aside, what method did you have in mind when you
wrote "Jobst's method in his book"?
Jobst's book recommends checking tension by using a tensiometer, by
plucking, by spoke-squeezing to see if the rim tacos "in two waves,"
or by tightening until the nipples can't be turned "easily":
FINAL TENSIONING
At this stage the wheel should be radially and laterally true and
centered, but not fully tensioned. To achieve greatest strength,
spokes should be tensioned near the maximum that the rim permits.
Spoke tension can be measured directly with a tensiometer, or it can
be determined by comparing the tone of the wheel to another properly
tensioned wheel with the same components. Pluck the spokes as
described in Tension by Tone (page 96). You can accurately match
tension among spokes to by matching their tone. Assuming the rim was
initially straight, all spokes on each side of a straight wheel should
give the same tone. For offset rear wheels, the spokes on the right
side should have a uniformly higher tone than those of the opposite
side. Nonuniform tone indicates a tension imbalance that will
eventually cause wheel misalignment.
FINDING THE RIGHT TENSION
The following method works well in determining proper spoke tension
for conventional road rims of up to 43 0 grams with 36 spokes. Tighten
all the spokes a quarter turn at a time, starting at the valve stem
hole. Once a distinct tone can be made by plucking, and spokes are not
easily squeezed together by grasping them in pairs, it is time to
check tension. After each round of tightening, test the tension by
stress relieving. If the wheel becomes untrue in two large waves
during stress relieving, the maximum, safe tension has been exceeded.
Approach this tension carefully to avoid major rim distortions. When
the wheel loses alignment from stress relieving, loosen all spokes a
half turn before retruing the wheel.
Stress relieving, discussed in a following section, increases tension
enough to overload the rim if the spokes are too tight. A strong and
safe wheel should be able to withstand about a ten percent overload
without damage. Note that tightening all spokes of an offset rear
wheel will move the rim away from the right side as described under
Wheels with Multiple Sprockets (page 100). Check centering and radial
and lateral alignment again. Only small corrections, if any, should be
required.
With large cross section mountain bike and deep section aero rims the
tension of 36 spokes may not exceed the strength of the rim. For such
heavy rims and conventional road rims using fewer than 32 spokes,
tensioning is usually at the limit when the nipples can no longer be
tightened easily.
--"The Bicycle Wheel," 3rd edition, p. 104-105
Cheers,
Carl Fogel
