Spokes tension with hot rim

On Tue, 27 Jan 2009 13:58:12 GMT, Brian Nystrom
wrote:

wrote:
Dear Sergio,

Probably not enough to regain the spoke tension lost when the the tire
was mounted and inflated.

Most wheels are built and tensioned bare, so their riding tension ends
up noticeably lower because of the tire constricts when inflated.

(Cheap wide single-wall MTB rims actually work the other way, gaining
spoke tension with higher tire pressure, but I expect that we're
talking about typical narrow 700c rims here.)

Here's Dianne's page showing how increased tire pressure lowered spoke
tension:

http://www.geocities.com/dianne_1234...-inflation.htm

Dianne found that 120 psi lowered 95 kgf bare-tire spoke tension ~13%
to 81 kgf.

Interesting. Just for laughs, I tried this on the front wheel of one of
my bikes, a Mavic GEL280 rim (36 hole tubular) laced to a Record hub
with DT Revolution spokes, with a Continental Sprinter tire. I pumped it
up to 100 psi (my normal riding pressure and stuck a Wheelsmith
tensiometer on it, then deflated the tire completely. It was really hard
to tell if the tensiometer reading moved at all, but if it did, it was a
matter of a few thousandths on the scale - essentially no difference.

Any idea why this is?

Is is just another tubular vs. clincher thing?

Are DT Revolutions magic spokes?

Is the Wheelsmith tensiometer junk?

The glue absorbs the difference?

They just don't make rims like they used to?

Dear Bryan,

Check a clincher, and check it at 120 psi.

If the Wheelsmith tension gauge doesn't show a difference on a
clincher at 120 psi, then the gauge is the problem. The Wheelsmith
gauge is a different design than the Park tension gauge and might
stick.

I'll be surprised if tubulars behave differently than clinchers. The
constriction is caused by the angle of the tire plies, which should be
the same. A good analogy is that the tire plies work like a scissors
jack as inflation expands them--notice how the scissors shorten as
they expand?

Here's a 24-second video of a Park gauge on a deflating MTB rim, which
is a wide single-wall rim that confusingly causes the tension to drop:
http://www.youtube.com/v/NeG5o3WX7Mw

That should give you an idea of how small a change a tension gauge
will show--the needle moves from a bit above mark 24 to just below it.

And the gauge will move the other way on a 700c rim. The wide
single-wall MTB rim behaves oddly because the tire ends up spreading
the V of the rim, pulling the spokes at the bottom of the V outward
more than the constriction pushes them inward.

Cheers,

Carl Fogel

On Sat, 24 Jan 2009 01:01:30 -0700, may have
said:

Such calculations would have to include the counter-effect of
increased tire constriction as the heated tire's pressure increases.

Given that your own testing demonstrated that the pressure gain due to
practically-likely temp changes is miniscule, the chances of that
factor making an important difference in the results seems small.

OTOH, none of these makes as much instantaneous difference in spoke
tension as the load/unload cycle that occurs during riding.

If someone is trying to factor in all of the potential contributors to
spoke tension change in a quest to try to find the highest possible
value to use for that characteristic in setting up their wheels, I
believe that they are in quest of a goal that is functionally not on
the target that they need to hit. The rim manufacturers generally
seem to have a pretty good idea of the correct tension to employ in
building wheels with their products. This is a case where chasing
after phantom improvements is possibly worse than a waste of time, and
seeking knowledge may not produce an increase in the seeker's
understanding, or ability to apply the data productively.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

On Sat, 24 Jan 2009 14:08:57 -0700, may have
said:

It's unlikely that spokes tensioned to ~85 kgf (with inflated tires)
double their tension due to rim heating on long downhills--the wheels
wouldn't be likely to reach the bottom.

Several explanations with a common theme suggest themselves.

A) The idiot doing the hasty calculations is off by a decimal place
somewhere, and the result should be a plausible ~8.5 kgf spoke tension
increase, not the implausbile ~85 kgf increase.

B) The idiot doing the hasty calculations is wasting his time with a
an over-simplified or completely mistaken model. The aluminum rim bed,
for example, will stretch inward, reducing how much the spokes stretch
outward. More likely, the idiot's assumptions about how things expand
against tension may have left engineers hospitalized with hernias from
uncontrollable laughter.

C) The idiot doing the hasty calculations is exquisitely correct and
should trust his figures instead of assuming that wheels would fail on
long downhills if rim heating doubled their spoke tension from ~85 kgf
to ~170 kgf. (But even an idiot finds this explanation hard to
swallow.)

Not to neglect...

D) The idiot forgot that the spokes are not laced radially, with the
result that the dimensional change effect is reduced somewhat.

(As if we needed yet another reason to dislike radial lacing.)

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

On Tue, 27 Jan 2009 12:11:19 -0600, Werehatrack
wrote:

On Sat, 24 Jan 2009 01:01:30 -0700, may have
said:

Such calculations would have to include the counter-effect of
increased tire constriction as the heated tire's pressure increases.

Given that your own testing demonstrated that the pressure gain due to
practically-likely temp changes is miniscule, the chances of that
factor making an important difference in the results seems small.

[snip]

Dear Werehatrack,

You may be thinking of a tire that I dipped in boiling water, which
produced no apparent pressure change. But that was just the contact
patch and intended to test claims about skidding, which involves only
the contact patch for a few seconds.

In this thread, we're talking about prolonged rim braking, which is a
much more impressive source of heat. Tim McNamara pointed out that
Angel Rodriguez put temperature-change stickers on tandem rims and
found ~250F in a very short time.

From ~70F to ~250F is roughly 530 Rankine to 710 Rankine, about 33%
higher absolute temperature and therefore probably about 33% higher
tire pressure. A 100 psi tire might see about 130 psi. That kind of
pressure increase would lead to noticeable tire constriction changes
in spoke tension.

Cheers,

Carl Fogel

wrote:
On Tue, 27 Jan 2009 13:58:12 GMT, Brian Nystrom
wrote:

wrote:
Dear Sergio,

Probably not enough to regain the spoke tension lost when the the tire
was mounted and inflated.

Most wheels are built and tensioned bare, so their riding tension ends
up noticeably lower because of the tire constricts when inflated.

(Cheap wide single-wall MTB rims actually work the other way, gaining
spoke tension with higher tire pressure, but I expect that we're
talking about typical narrow 700c rims here.)

Here's Dianne's page showing how increased tire pressure lowered spoke
tension:

http://www.geocities.com/dianne_1234...-inflation.htm

Dianne found that 120 psi lowered 95 kgf bare-tire spoke tension ~13%
to 81 kgf.
Interesting. Just for laughs, I tried this on the front wheel of one of
my bikes, a Mavic GEL280 rim (36 hole tubular) laced to a Record hub
with DT Revolution spokes, with a Continental Sprinter tire. I pumped it
up to 100 psi (my normal riding pressure and stuck a Wheelsmith
tensiometer on it, then deflated the tire completely. It was really hard
to tell if the tensiometer reading moved at all, but if it did, it was a
matter of a few thousandths on the scale - essentially no difference.

Any idea why this is?

Is is just another tubular vs. clincher thing?

Are DT Revolutions magic spokes?

Is the Wheelsmith tensiometer junk?

The glue absorbs the difference?

They just don't make rims like they used to?

Dear Bryan,

Check a clincher, and check it at 120 psi.

I would, but that wouldn't mean much to me, as I only ride tubulars on
the road and I never inflate the front wheel to more than 105 psi,
usually 95-100. If this phenomenon doesn't affect the performance of my
wheels under the conditions I use them, I really don't care about it.

Do any of you have tubulars you can test this on?

If the Wheelsmith tension gauge doesn't show a difference on a
clincher at 120 psi, then the gauge is the problem. The Wheelsmith
gauge is a different design than the Park tension gauge and might
stick.

I can believe that. I tried it again using the method that Jim
suggested. It revealed a very slight variation from reading to reading,
but still no obvious difference between 0 and 100 psi.

BTW, this was tested on a radial-laced wheel, which I would assume would
be a worst-case scenario.

I'll be surprised if tubulars behave differently than clinchers. The
constriction is caused by the angle of the tire plies, which should be
the same. A good analogy is that the tire plies work like a scissors
jack as inflation expands them--notice how the scissors shorten as
they expand?

Ah, that sounds like a plausible explanation. I guess what we need is
"radial" bike tires, eh?

Here's a 24-second video of a Park gauge on a deflating MTB rim, which
is a wide single-wall rim that confusingly causes the tension to drop:
http://www.youtube.com/v/NeG5o3WX7Mw

That should give you an idea of how small a change a tension gauge
will show--the needle moves from a bit above mark 24 to just below it.

And the gauge will move the other way on a 700c rim. The wide
single-wall MTB rim behaves oddly because the tire ends up spreading
the V of the rim, pulling the spokes at the bottom of the V outward
more than the constriction pushes them inward.

Just for yucks, I tested this on a Mavic CrossMax wheel with a tubeless
tire, with the gauge set across the narrow (more flexible) dimension of
the spoke. I checked it at 40 psi (the most I ever run in the tires) and
at zero. There was a very slight gain in tension - considerably less
than 1Kgf - at zero psi.

All I can conclude at this point is that for the wheels I ride at the
pressures I use, this phenomenon is insignificant.

On Wed, 28 Jan 2009 15:17:10 GMT, Brian Nystrom
wrote:

wrote:
On Tue, 27 Jan 2009 13:58:12 GMT, Brian Nystrom
wrote:

wrote:
Dear Sergio,

Probably not enough to regain the spoke tension lost when the the tire
was mounted and inflated.

Most wheels are built and tensioned bare, so their riding tension ends
up noticeably lower because of the tire constricts when inflated.

(Cheap wide single-wall MTB rims actually work the other way, gaining
spoke tension with higher tire pressure, but I expect that we're
talking about typical narrow 700c rims here.)

Here's Dianne's page showing how increased tire pressure lowered spoke
tension:

http://www.geocities.com/dianne_1234...-inflation.htm

Dianne found that 120 psi lowered 95 kgf bare-tire spoke tension ~13%
to 81 kgf.
Interesting. Just for laughs, I tried this on the front wheel of one of
my bikes, a Mavic GEL280 rim (36 hole tubular) laced to a Record hub
with DT Revolution spokes, with a Continental Sprinter tire. I pumped it
up to 100 psi (my normal riding pressure and stuck a Wheelsmith
tensiometer on it, then deflated the tire completely. It was really hard
to tell if the tensiometer reading moved at all, but if it did, it was a
matter of a few thousandths on the scale - essentially no difference.

Any idea why this is?

Is is just another tubular vs. clincher thing?

Are DT Revolutions magic spokes?

Is the Wheelsmith tensiometer junk?

The glue absorbs the difference?

They just don't make rims like they used to?

Dear Bryan,

Check a clincher, and check it at 120 psi.

I would, but that wouldn't mean much to me, as I only ride tubulars on
the road and I never inflate the front wheel to more than 105 psi,
usually 95-100. If this phenomenon doesn't affect the performance of my
wheels under the conditions I use them, I really don't care about it.

Do any of you have tubulars you can test this on?

If the Wheelsmith tension gauge doesn't show a difference on a
clincher at 120 psi, then the gauge is the problem. The Wheelsmith
gauge is a different design than the Park tension gauge and might
stick.

I can believe that. I tried it again using the method that Jim
suggested. It revealed a very slight variation from reading to reading,
but still no obvious difference between 0 and 100 psi.

BTW, this was tested on a radial-laced wheel, which I would assume would
be a worst-case scenario.

I'll be surprised if tubulars behave differently than clinchers. The
constriction is caused by the angle of the tire plies, which should be
the same. A good analogy is that the tire plies work like a scissors
jack as inflation expands them--notice how the scissors shorten as
they expand?

Ah, that sounds like a plausible explanation. I guess what we need is
"radial" bike tires, eh?

Here's a 24-second video of a Park gauge on a deflating MTB rim, which
is a wide single-wall rim that confusingly causes the tension to drop:
http://www.youtube.com/v/NeG5o3WX7Mw

That should give you an idea of how small a change a tension gauge
will show--the needle moves from a bit above mark 24 to just below it.

And the gauge will move the other way on a 700c rim. The wide
single-wall MTB rim behaves oddly because the tire ends up spreading
the V of the rim, pulling the spokes at the bottom of the V outward
more than the constriction pushes them inward.

Just for yucks, I tested this on a Mavic CrossMax wheel with a tubeless
tire, with the gauge set across the narrow (more flexible) dimension of
the spoke. I checked it at 40 psi (the most I ever run in the tires) and
at zero. There was a very slight gain in tension - considerably less
than 1Kgf - at zero psi.

All I can conclude at this point is that for the wheels I ride at the
pressures I use, this phenomenon is insignificant.

Dear Bryan,

Or that your Wheelsmith gauge sticks.

Try it on a clincher to see if it works.

Cheers,

Carl Fogel

wrote:
On Wed, 28 Jan 2009 15:17:10 GMT, Brian Nystrom
wrote:

wrote:
On Tue, 27 Jan 2009 13:58:12 GMT, Brian Nystrom
wrote:

wrote:
Dear Sergio,

Probably not enough to regain the spoke tension lost when the the tire
was mounted and inflated.

Most wheels are built and tensioned bare, so their riding tension ends
up noticeably lower because of the tire constricts when inflated.

(Cheap wide single-wall MTB rims actually work the other way, gaining
spoke tension with higher tire pressure, but I expect that we're
talking about typical narrow 700c rims here.)

Here's Dianne's page showing how increased tire pressure lowered spoke
tension:

http://www.geocities.com/dianne_1234...-inflation.htm

Dianne found that 120 psi lowered 95 kgf bare-tire spoke tension ~13%
to 81 kgf.
Interesting. Just for laughs, I tried this on the front wheel of one of
my bikes, a Mavic GEL280 rim (36 hole tubular) laced to a Record hub
with DT Revolution spokes, with a Continental Sprinter tire. I pumped it
up to 100 psi (my normal riding pressure and stuck a Wheelsmith
tensiometer on it, then deflated the tire completely. It was really hard
to tell if the tensiometer reading moved at all, but if it did, it was a
matter of a few thousandths on the scale - essentially no difference.

Any idea why this is?

Is is just another tubular vs. clincher thing?

Are DT Revolutions magic spokes?

Is the Wheelsmith tensiometer junk?

The glue absorbs the difference?

They just don't make rims like they used to?
Dear Bryan,

Check a clincher, and check it at 120 psi.
I would, but that wouldn't mean much to me, as I only ride tubulars on
the road and I never inflate the front wheel to more than 105 psi,
usually 95-100. If this phenomenon doesn't affect the performance of my
wheels under the conditions I use them, I really don't care about it.

Do any of you have tubulars you can test this on?

If the Wheelsmith tension gauge doesn't show a difference on a
clincher at 120 psi, then the gauge is the problem. The Wheelsmith
gauge is a different design than the Park tension gauge and might
stick.
I can believe that. I tried it again using the method that Jim
suggested. It revealed a very slight variation from reading to reading,
but still no obvious difference between 0 and 100 psi.

BTW, this was tested on a radial-laced wheel, which I would assume would
be a worst-case scenario.

I'll be surprised if tubulars behave differently than clinchers. The
constriction is caused by the angle of the tire plies, which should be
the same. A good analogy is that the tire plies work like a scissors
jack as inflation expands them--notice how the scissors shorten as
they expand?
Ah, that sounds like a plausible explanation. I guess what we need is
"radial" bike tires, eh?

Here's a 24-second video of a Park gauge on a deflating MTB rim, which
is a wide single-wall rim that confusingly causes the tension to drop:
http://www.youtube.com/v/NeG5o3WX7Mw

That should give you an idea of how small a change a tension gauge
will show--the needle moves from a bit above mark 24 to just below it.

And the gauge will move the other way on a 700c rim. The wide
single-wall MTB rim behaves oddly because the tire ends up spreading
the V of the rim, pulling the spokes at the bottom of the V outward
more than the constriction pushes them inward.
Just for yucks, I tested this on a Mavic CrossMax wheel with a tubeless
tire, with the gauge set across the narrow (more flexible) dimension of
the spoke. I checked it at 40 psi (the most I ever run in the tires) and
at zero. There was a very slight gain in tension - considerably less
than 1Kgf - at zero psi.

All I can conclude at this point is that for the wheels I ride at the
pressures I use, this phenomenon is insignificant.

Dear Bryan,

Or that your Wheelsmith gauge sticks.

No, that's not a problem, as I took multiple readings, removing and
replacing the gauge every time. It works smoothly.

Try it on a clincher to see if it works.

I don't have any to test. Seriously, I don't own any road clinchers.

On Thu, 29 Jan 2009 15:59:09 GMT, Brian Nystrom
wrote:

wrote:
On Wed, 28 Jan 2009 15:17:10 GMT, Brian Nystrom

[snip]

Dear Bryan,

Or that your Wheelsmith gauge sticks.

No, that's not a problem, as I took multiple readings, removing and
replacing the gauge every time. It works smoothly.

Try it on a clincher to see if it works.

I don't have any to test. Seriously, I don't own any road clinchers.

Dear Bryan,

Let us know when you manage to find a 700c clincher tire.

Seriously.

:-)

Cheers,

Carl Fogel