Tensiometer curiosity

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

On Sat, 31 Mar 2007 08:56:12 -0700, jim beam
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

On Mar 31, 11:23 am, jim beam 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.

On Mar 31, 11:34 am, 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?

On 2007-03-31, jim beam wrote:
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.

In article ,
jim beam 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.

In article ,
Ben C wrote:

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.

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.

In article .com,
"Ron Ruff" 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.

On Mar 31, 4:18 pm, Tim McNamara 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.

Ron Ruff wrote:
On Mar 31, 11:23 am, jim beam 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.

in theory, yes. as pointed out by others, there's often a tiny flat
spot where the weld flashing is machined off, and using a truing stand
like a ts2 doesn't exactly emphasize the problem, but with every welded
rim i've built, it's needed higher tension for the 2 spokes at the join.
i build with an attachment to my ts2 so i have a proper handle on radial
trueness, not just lateral, which is all that stand really does.