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In article <[email hidden]>,

Tim McNamara said:

In article <[email hidden]>,

(Luns Tee) said:

I'll start with saying that it's still not entirely clear to me how
the clinch works.

As I said in the other thread, to me it looks like an interference fit
comprised of the hook at the edge of the rim with the bead of the tire
below it. The inner tube fills the space like a fluid, pressing the
tire against the rim wall and securing the clinch. The inelastic bead
inside the edge of the tire if important as it would resist the tendency
of the inner tube to push the tire away from the rim bed by preventing
the edge of the tire casing from stretching.

What's unclear to me is what keeps the bead from just sliding out
of the space under the rim hook: it's seems to me somewhat like tying
a knot in end of a rope and trying to use that bump in the rope as a
grappling hook. Air pressure pressing the tire against the rim wall
doesn't help except for pressure right at the bead, a strip of only a
millimetre or two high. It's like pressing on the knotted string:
pushing it against the wall doesn't help, but pushing it at the knot
when it wants to otherwise slide off the corner it's snagged on, does.

Perhaps that mm wide strip is important to this picture - I'd
dismissed it before given how thin it is, but it's worth considering.
The force on that strip would be proportional to air pressure, so if
we increase air pressure, but keep casing tension constant (by going
to a narrower tire as we increase pressure), the tire should be more
resistant to blowoff.
Thank you for bringing this to light, Tim. I take back what I'd
said earlier about tire width not mattering if casing tension is kept
constant: this does suggest that narrow tires would be more resistant to
blowoffs.

Quoted message said:

A while back, the folks at Rivendell tried cutting the beads and
inflating the tires. I don't have the article in front of me, but the
tires were retained on the rim to surprisingly high pressures IIRC, but
eventually blew off the rim, tearing the casing at one or more of the
cuts. That suggests to me that the interference fit at the clinch is
very effective, and that at higher pressures the inelasticity of the
bead wire becomes more important.

Jobst and Damon Rinard have mentioned that experiment too, and
it does show the clinch is quite effective. But given that blowoffs
still occur, there's still room to improve.

-Luns

Tim McNamara said:

Quoted message said:

I'll start with saying that it's still not entirely clear to me how
the clinch works.

Quoted message said:

As I said in the other thread, to me it looks like an interference
fit comprised of the hook at the edge of the rim with the bead of
the tire below it. The inner tube fills the space like a fluid,
pressing the tire against the rim wall and securing the clinch. The
inelastic bead inside the edge of the tire if important as it would
resist the tendency of the inner tube to push the tire away from the
rim bed by preventing the edge of the tire casing from stretching.

Quoted message said:

A while back, the folks at Rivendell tried cutting the beads and
inflating the tires. I don't have the article in front of me, but
the tires were retained on the rim to surprisingly high pressures
IIRC, but eventually blew off the rim, tearing the casing at one or
more of the cuts. That suggests to me that the interference fit at
the clinch is very effective, and that at higher pressures the
in-elasticity of the bead wire becomes more important.

That was my experiment and Sheldon put it on his web site after Damon
Rinard repeated the experiment.

http://www.sheldonbrown.com/rinard/tirebead.htm

Jobst Brandt

Jobst Brandt said:

Quoted message said:

If the tires were intended for straight wall rims, I would expect
the bead wires to be somewhat heavier than typical tires of today,
and the radial load of the bead supported entirely by the wire.

Quoted message said:

That's because you have never seen s steel bead tire blow off a rim at
normal inflation pressure. They do that and I have had two of these
on my bicycle, not to mention all the tandem riders who have had this
occur. The steel bead is not what holds the tire on a clincher rim.

Quoted message said:

http://www.sheldonbrown.com/rinard/tirebead.htm

I had straight walled rims on my first two road bikes. The first bike was a
hand me down from about 1970 with wide 27" Weinmann rims and medium pressure
1-1/4" tires - ordinary for the era. The second bike was an '84 Miyata 912
with ~20 mm wide Araya box section rims that looked like MA-2s except
without the hooked edges. Narrow tires were in fashion then, so the bike
came with 20 mm wide tires, and my subsequent replacement tires were also
the same width. I used 100 psi in the tires and never had a blowout. At
the time, I was a sophmore in high school and rode the Hicks Road loop every
day after school, so in retrospect, it was a good thing that I didn't have
wider tires!

I would be interesting to repeat the cut bead test with straight sided rims.
Would constriction alone be enough to retain the tire with 20 mm tires? My
Miyata was stolen in '87, so I'm going off memory for the rim description,
but I remember wondering about the difference after seeing hooked edges for
the first time on the bike that I got in '86 or '87.

Quoted message said:

Luns Tee writes:

[snip]

Quoted message said:

Quoted message said:

Quoted message said:

> If you want a test, look at the edge of the chafing strip just
> above at the lip of the rim as you inflate a tire. I tried this
> just now. My tire's edge is only barely visible when inflated at
> 20 psi, enough pressure to give the tire its intended shape.
> Inflating to 100psi, the strip is pulled out and about 1mm of it
> is now visible. This is with a Kevlar-bead tire: a steel-bead
> tire may show less of a difference.

Quoted message said:

Quoted message said:

I think you overcame friction. Did you let the pressure back down
to the lower level and see it return to that position?

Quoted message said:

It's a full cycle. Letting the pressure out, the strip retracts to
where it started. Try it yourself.

I cannot detect any change between 100psi and 10psi using a magnifying
glass, the lower pressure being just enough for the tire to not
collapse from its round cross section.

[snip]

Dear Luns and Jobst,

It's raining, so I had some fun with a tire and my camera on a stand.

I used a fine-point red sharpy pen to cross-hatch the sidewall at the
bead on a Kevlar-bead 700x26 tire. Then I took 4 pictures at 1 psi, 40
psi, 85 psi, 120 psi, and back down around 15 psi.

It looks as if the middle /\ of the lowest cross-hatching is creeping
out into sight as pressure increases, and creeping back out of sight
when pressure is reduced.

1 psi, scarcely any inflation:
http://server6.theimagehosting.com/image.php?img=237a001psi.jpg

40 psi:
http://server6.theimagehosting.com/image.php?img=238a040psi.jpg

85 psi:
http://server6.theimagehosting.com/image.php?img=239a085psi.jpg

120 psi:
http://server6.theimagehosting.com/image.php?img=240a120psi.jpg

Back down to 15 psi, focus poor, but good enough:
http://server6.theimagehosting.com/image.php?img=241abackdownto15psi.jpg

Again, look for the middle /\ of the lowest cross-hatching.

A steel-bead tire might not stretch this much, as Luns suggests.

Cycling pressure might change matters, as Jobst suggests.

If friction prevents the bead from creeping back, then friction could
just as easily prevent the bead from creeping out. The experiment may
be trickier than it looks.

Could it be that the visible part of the sidewall does stretch enough
to be seen, but the part of the sidewal actually out of sight and
touching the rim is pinned flat by the air pressure?
____
\
tire/
/
/
/
x | x possible hard-to-see freer area
|=| |=| means tire-rim pressed firmly together
|=|
/
/
rim

Cheers,

Carl Fogel

Andrew Lee said:

Quoted message said:

Quoted message said:

If the tires were intended for straight wall rims, I would expect
the bead wires to be somewhat heavier than typical tires of today,
and the radial load of the bead supported entirely by the wire.

Quoted message said:

Quoted message said:

That's because you have never seen s steel bead tire blow off a rim
at normal inflation pressure. They do that and I have had two of
these on my bicycle, not to mention all the tandem riders who have
had this occur. The steel bead is not what holds the tire on a
clincher rim.

http://www.sheldonbrown.com/rinard/tirebead.htm

Quoted message said:

I had straight walled rims on my first two road bikes. The first
bike was a hand me down from about 1970 with wide 27" Weinmann rims
and medium pressure 1-1/4" tires - ordinary for the era. The second
bike was an '84 Miyata 912 with ~20 mm wide Araya box section rims
that looked like MA-2s except without the hooked edges. Narrow
tires were in fashion then, so the bike came with 20 mm wide tires,
and my subsequent replacement tires were also the same width. I
used 100 psi in the tires and never had a blowout. At the time, I
was a sophomore in high school and rode the Hicks Road loop every day
after school, so in retrospect, it was a good thing that I didn't
have wider tires!

Quoted message said:

I would be interesting to repeat the cut bead test with straight
sided rims. Would constriction alone be enough to retain the tire
with 20 mm tires? My Miyata was stolen in '87, so I'm going off
memory for the rim description, but I remember wondering about the
difference after seeing hooked edges for the first time on the bike
that I got in '86 or '87.

Hicks road is steep enough and long enough so that in the days of yore
tubular glue was a significant problem. We didn't have good clinchers
when we rode down from the top of Mt. Umunhum and I guess we should be
glad, because I think we would have had a tire blow off.

I haven't made any measurements, but the constriction of clinchers is
a major asset in holding them on the rim. In contrast, the cut bead
experiment on the tire in the web site shows that it is not the wire
in the bead that keeps the tire in place.

Jobst Brandt

Carl Fogel said:

[snip]

Quoted message said:

Quoted message said:

Quoted message said:

>> If you want a test, look at the edge of the chafing strip just
>> above at the lip of the rim as you inflate a tire. I tried this
>> just now. My tire's edge is only barely visible when inflated at
>> 20 psi, enough pressure to give the tire its intended shape.
>> Inflating to 100psi, the strip is pulled out and about 1mm of it
>> is now visible. This is with a Kevlar-bead tire: a steel-bead
>> tire may show less of a difference.

Quoted message said:

Quoted message said:

Quoted message said:

> I think you overcame friction. Did you let the pressure back down
> to the lower level and see it return to that position?

Quoted message said:

Quoted message said:

Quoted message said:

It's a full cycle. Letting the pressure out, the strip retracts to
where it started. Try it yourself.

Quoted message said:

Quoted message said:

I cannot detect any change between 100psi and 10psi using a magnifying
glass, the lower pressure being just enough for the tire to not
collapse from its round cross section.

Quoted message said:

[snip]

Quoted message said:

It's raining, so I had some fun with a tire and my camera on a
stand.

Quoted message said:

I used a fine-point red sharpy pen to cross-hatch the sidewall at
the bead on a Kevlar-bead 700x26 tire. Then I took 4 pictures at 1
psi, 40 psi, 85 psi, 120 psi, and back down around 15 psi.

Quoted message said:

It looks as if the middle /\ of the lowest cross-hatching is
creeping out into sight as pressure increases, and creeping back out
of sight when pressure is reduced.

Quoted message said:

1 psi, scarcely any inflation:

http://server6.theimagehosting.com/image.php?img=237a001psi.jpg

Quoted message said:

40 psi:

http://server6.theimagehosting.com/image.php?img=238a040psi.jpg

Quoted message said:

85 psi:

http://server6.theimagehosting.com/image.php?img=239a085psi.jpg

Quoted message said:

120 psi:

http://server6.theimagehosting.com/image.php?img=240a120psi.jpg

Quoted message said:

Back down to 15 psi, focus poor, but good enough:

http://server6.theimagehosting.com/image.php?img=241abackdownto15psi.jpg

Quoted message said:

Again, look for the middle /\ of the lowest cross-hatching.

Quoted message said:

A steel-bead tire might not stretch this much, as Luns suggests.

Quoted message said:

Cycling pressure might change matters, as Jobst suggests.

Nice work! My observations were made on a tire that had plenty of
miles on and I ran it from about 10psi to 100psi and back down to
10psi and could see not difference. It is a steel bead tire, but then
the tire I cut the steel wire on also did not make any visible
difference when inflated to 100psi.

I can't explain the difference.

Quoted message said:

If friction prevents the bead from creeping back, then friction
could just as easily prevent the bead from creeping out. The
experiment may be trickier than it looks.

Well, friction would be overcome while riding because we know that the
tire frets on the chafing strip and would release any friction drag.
That is shown by the aluminum and aluminum oxide on the chafing strip.

Quoted message said:

Could it be that the visible part of the sidewall does stretch
enough to be seen, but the part of the sidewall actually out of
sight and touching the rim is pinned flat by the air pressure?

I doubt it. The cord angle isn't changing nor is the red marker.

Quoted message said:

____
\
tire/
/
/
/
x | x possible hard-to-see freer area
|=| |=| means tire-rim pressed firmly together
|=|
/
/
rim

Jobst Brandt

In article <[email hidden]>,

Quoted message said:

I used a fine-point red sharpy pen to cross-hatch the sidewall at the
bead on a Kevlar-bead 700x26 tire. Then I took 4 pictures at 1 psi, 40
psi, 85 psi, 120 psi, and back down around 15 psi.

Thank you, Carl. You are my hero.

Quoted message said:

If friction prevents the bead from creeping back, then friction could
just as easily prevent the bead from creeping out. The experiment may
be trickier than it looks.

Friction would introduce hysteresis, but given that we've
observed changes in both directions, the motion has been enough to
overcome it. The only trick that friction introduces is that the
observed position after inflating to a given pressure could be different
from the position after deflating to that pressure.

Quoted message said:

Could it be that the visible part of the sidewall does stretch enough
to be seen, but the part of the sidewal actually out of sight and
touching the rim is pinned flat by the air pressure?

There's only a few mm of casing from the bead to what we
observe, an even if all of it were stretching, if it stretched enough to
make this big of a difference, we would see the tire's minor diameter
also change significantly.
As it is, the tire's minor diameter would increase ever so
slightly with inflation, from there being this tiny bit more casing
available for its circumference.

-Luns

In article <[email hidden]>,

Quoted message said:

Nice work! My observations were made on a tire that had plenty of
miles on and I ran it from about 10psi to 100psi and back down to
10psi and could see not difference. It is a steel bead tire, but then
the tire I cut the steel wire on also did not make any visible
difference when inflated to 100psi.

I can't explain the difference.

Your steel bead is on the order of 5x as stiff as the kevlar
making this motion harder to observe, and friction may be masking what's
left. Also, it may be that your beads are a better fit for the rim
hook, having less space to expand into than Carl or my tires' beads.

The cut bead is unable to hold any tension of its own, so with
any casing tension at all, expands to make contact with the rim hooks.
From that point on, the bead is restrained and all casing tension is
transferred to the rim by the clinch.

-Luns