HED H3 tire blow off

I know about the warning from hed about certain clincher tires but
would just like to add my experinces and ask if anybody knows what the
answer is?

I have had a HED H3 clincher rear wheel for a few years now and this
year bought a matching front.

I have had the rear tire blow off suddenly, causing a large bang a few
times usually after an event.

When I first got the front wheel I was getting punctures near the
valve hole before, during or after every event so after getting some
advice from freinds filed the valve hole and put some rim tape on
(even though I have no spoke holes). This seems to have stopped the
problem.

However, today right after finishing a 25 mile TT the rear tire blew
off the rim (with the usual large bang). The tire is a vittoria evo
KS (700c x 20). The tire seemed reasonably tight to get on the wheel
(I have rime tape on this wheel too).

Anybody got any tips to avoid this as I really don't want it to happen
at 35mph!

MTIA

Dan

nospam wrote:

I know about the warning from hed about certain clincher tires but
would just like to add my experinces and ask if anybody knows what the
answer is?

I have had a HED H3 clincher rear wheel for a few years now and this
year bought a matching front.

I have had the rear tire blow off suddenly, causing a large bang a few
times usually after an event.

When I first got the front wheel I was getting punctures near the
valve hole before, during or after every event so after getting some
advice from freinds filed the valve hole and put some rim tape on
(even though I have no spoke holes). This seems to have stopped the
problem.

However, today right after finishing a 25 mile TT the rear tire blew
off the rim (with the usual large bang). The tire is a vittoria evo
KS (700c x 20). The tire seemed reasonably tight to get on the wheel
(I have rime tape on this wheel too).

Anybody got any tips to avoid this as I really don't want it to happen
at 35mph!

Is the rim damaged in any way? Are you using *really* high pressures
like 180psi?

The rim appears to be OK. I only ever pump tires up to around 120 psi
although they are rated higher. I have noticed I have narrow rim tape
that does not go up to the edge of the rim. I may try putting some
wider rim tape in (velox).

Was looking at the reviews for the conti supersonic tires on
roadbikereview.com and noticed some people are having trouble with
these tires combined with ksyriums.

On Sun, 09 May 2004 18:26:57 +0100, Zog The Undeniable
wrote:

nospam wrote:

I know about the warning from hed about certain clincher tires but
would just like to add my experinces and ask if anybody knows what the
answer is?

I have had a HED H3 clincher rear wheel for a few years now and this
year bought a matching front.

I have had the rear tire blow off suddenly, causing a large bang a few
times usually after an event.

When I first got the front wheel I was getting punctures near the
valve hole before, during or after every event so after getting some
advice from freinds filed the valve hole and put some rim tape on
(even though I have no spoke holes). This seems to have stopped the
problem.

However, today right after finishing a 25 mile TT the rear tire blew
off the rim (with the usual large bang). The tire is a vittoria evo
KS (700c x 20). The tire seemed reasonably tight to get on the wheel
(I have rime tape on this wheel too).

Anybody got any tips to avoid this as I really don't want it to happen
at 35mph!

Is the rim damaged in any way? Are you using *really* high pressures
like 180psi?

Dan Oatandpolos writes:

I know about the warning from HED about certain clincher tires but
would just like to add my experiences and ask if anybody knows what
the answer is?

I have had a HED H3 clincher rear wheel for a few years now and this
year bought a matching front.

I have had the rear tire blow off suddenly, causing a large bang a
few times usually after an event.

However, today right after finishing a 25 mile TT the rear tire blew
off the rim (with the usual large bang). The tire is a Vittoria evo
KS (700c x 20). The tire seemed reasonably tight to get on the wheel
(I have rime tape on this wheel too).

Anybody got any tips to avoid this as I really don't want it to
happen at 35mph!

You may be having typical tube inclusions in your tire mounting
procedure. This can be seen when you inflate the tire to operating
pressure and spin the wheel. If the bead of the tire is not uniformly
spaced from the rim, the tube is most likely wedged between tire bead
and rim at the high location. This will eventually blow the tire off.

Quite aside from that, tire cross section size has practically no
effect on a tire's propensity to blow-off the rim. That is dependent
on pressure and rim bead shape only. Separating force depends
entirely on internal width of the rim and tire pressure. That effect
is the same regardless of tire cross section.

For descending steep roads where the ratio between braking and air
speed (cooling) is poor, such as on rough roads that do not allow
higher speeds than 15MPH, inflation pressure should be kept below 100
psi to avoid tire blow-off. I often read of tires inflated to
120-140psi and wonder what sort of steep, hard braking descents these
riders experience, having seen and experienced plenty of blow-offs at
100+psi on such descents. Tandems are special cases that should
always have a hub brake to make such descents safe.

Jobst Brandt

Just to add I have been trying a couple of different makes and models
of tires on a wheel and have noticed that some are quite tight with
just 1 bead mounted, others I can fit a finger underneath. It seems
there is considerable difference in manufacturers (possibly different
models, same manufacturer?) tolerances for bead diameter.

I will be sticking to tight tires from now on and see how I get on.
Also I'm gonna stop using latex tubes because I feel it is easier for
'tube inclusions' to occur.

I'll let you know how I get on.
Thanks



On Mon, 10 May 2004 05:13:47 GMT,
wrote:

Dan Oatandpolos writes:

I know about the warning from HED about certain clincher tires but
would just like to add my experiences and ask if anybody knows what
the answer is?

I have had a HED H3 clincher rear wheel for a few years now and this
year bought a matching front.

I have had the rear tire blow off suddenly, causing a large bang a
few times usually after an event.

However, today right after finishing a 25 mile TT the rear tire blew
off the rim (with the usual large bang). The tire is a Vittoria evo
KS (700c x 20). The tire seemed reasonably tight to get on the wheel
(I have rime tape on this wheel too).

Anybody got any tips to avoid this as I really don't want it to
happen at 35mph!

You may be having typical tube inclusions in your tire mounting
procedure. This can be seen when you inflate the tire to operating
pressure and spin the wheel. If the bead of the tire is not uniformly
spaced from the rim, the tube is most likely wedged between tire bead
and rim at the high location. This will eventually blow the tire off.

Quite aside from that, tire cross section size has practically no
effect on a tire's propensity to blow-off the rim. That is dependent
on pressure and rim bead shape only. Separating force depends
entirely on internal width of the rim and tire pressure. That effect
is the same regardless of tire cross section.

For descending steep roads where the ratio between braking and air
speed (cooling) is poor, such as on rough roads that do not allow
higher speeds than 15MPH, inflation pressure should be kept below 100
psi to avoid tire blow-off. I often read of tires inflated to
120-140psi and wonder what sort of steep, hard braking descents these
riders experience, having seen and experienced plenty of blow-offs at
100+psi on such descents. Tandems are special cases that should
always have a hub brake to make such descents safe.

Jobst Brandt

Dan Oatandpolos writes:

Just to add I have been trying a couple of different makes and
models of tires on a wheel and have noticed that some are quite
tight with just 1 bead mounted, others I can fit a finger
underneath. It seems there is considerable difference in
manufacturers (possibly different models, same manufacturer?)
tolerances for bead diameter.

I will be sticking to tight tires from now on and see how I get on.
Also I'm gonna stop using latex tubes because I feel it is easier
for 'tube inclusions' to occur.

Oops! This subject has been discussed here often enough and I and
Damon Rinard performed tests to show that tire fit has little to do
with retention with over inflation caused by brake heating. We both
cut the steel bead wire in six or more places before mounting the tire
on a rim. Inflation to normal running pressure did not dislodge the
tire. Because the casing is damaged by this experiment, the tires were
not ridden in that condition.

I'll let you know how I get on.

That won't help much because such experimentation needs to have
controls and a clear definition of what went into it. Just riding
such a tire leaves this out in most (overwhelming majority of) cases.

On Wed, 12 May 2004 21:54:33 +0100,
wrote:


On Mon, 10 May 2004 05:13:47 GMT,
wrote:
For descending steep roads where the ratio between braking and air
speed (cooling) is poor, such as on rough roads that do not allow
higher speeds than 15MPH, inflation pressure should be kept below 100
psi to avoid tire blow-off. I often read of tires inflated to
120-140psi and wonder what sort of steep, hard braking descents these
riders experience, having seen and experienced plenty of blow-offs at
100+psi on such descents. Tandems are special cases that should
always have a hub brake to make such descents safe.

Jobst Brandt



If a tyre has 100psi at 20C (68F), it need to get to about 80C (176F)
to increase the pressure to 120psi. This seems unlikely as the tyre is
cooled by conduction to the road surface. As the rim will probably
always be hotter than the tyre under braking, thermal expansion
shouldn't loosen the tyre fit either. Do you know why tyres blow off
on descents? Is there a significant difference in failure rate
depending on bead material? Does the valve stem lock the tyre to the
rim at one point and the rest of the tyre creeps round the rim due to
braking force? Just curious to know whether there is any rigorous
research into failure mode and cause.


Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary

wrote in message
...
Just riding
such a tire leaves this out in most
(overwhelming majority of) cases.
^^^^^^^^^^^^^^^^^^^^^

LOL!

On Thu, 13 May 2004 09:07:18 GMT, Kinky Cowboy
wrote:

On Wed, 12 May 2004 21:54:33 +0100,
wrote:


On Mon, 10 May 2004 05:13:47 GMT,
wrote:
For descending steep roads where the ratio between braking and air
speed (cooling) is poor, such as on rough roads that do not allow
higher speeds than 15MPH, inflation pressure should be kept below 100
psi to avoid tire blow-off. I often read of tires inflated to
120-140psi and wonder what sort of steep, hard braking descents these
riders experience, having seen and experienced plenty of blow-offs at
100+psi on such descents. Tandems are special cases that should
always have a hub brake to make such descents safe.

Jobst Brandt



If a tyre has 100psi at 20C (68F), it need to get to about 80C (176F)
to increase the pressure to 120psi. This seems unlikely as the tyre is
cooled by conduction to the road surface. As the rim will probably
always be hotter than the tyre under braking, thermal expansion
shouldn't loosen the tyre fit either. Do you know why tyres blow off
on descents? Is there a significant difference in failure rate
depending on bead material? Does the valve stem lock the tyre to the
rim at one point and the rest of the tyre creeps round the rim due to
braking force? Just curious to know whether there is any rigorous
research into failure mode and cause.


Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary

Dear Kinky,

I assume that you're using the relative temperatures in degrees Kelvin
to obtain a 100/120 psi ratio for termperatures 293/353 K, which seems
to make sense.

But the absolute effect of heat on gas pressure is greater at higher
initial pressures. If a 100 psi tire goes to 120 psi, then a tire that
started out at 125 psi goes to 150 psi. It's only a 5-pound
difference, but with bicycle tires we tend to feel comfortable about
100 to 120 psi, but start to worry when 125 psi rises to 150 psi.

There may be another heat source. The brake pads heat up the rim on a
descent, and that's what we notice. But the tire's contact patch is
braking just as hard against the pavement and also rolling a steady
bulge through the tire--it squashes out under braking load far more
than just rolling freely along.

These descents may also involve stretches of pavement hot enough to
fry eggs on. Blacktop sitting in the sun all day is usually much
warmer than the pleasant mountain breeze.

The tire may also act as an insulator, trapping heat. Car tires
running at much higher speeds with much higher loads have speed
ratings related to expected temperatures. The car tires fail far more
often in summer temperatures.

It's possible that the blow-offs are due not just to higher pressure,
but also o the tires themselves deteriorating at the higher
temperatures, the bead material question that you raise.

Thanks for asking an interesting question.

Carl Fogel

On Thu, 13 May 2004 09:07:18 GMT, Kinky Cowboy
wrote:

On Wed, 12 May 2004 21:54:33 +0100,
wrote:


On Mon, 10 May 2004 05:13:47 GMT,
wrote:
For descending steep roads where the ratio between braking and air
speed (cooling) is poor, such as on rough roads that do not allow
higher speeds than 15MPH, inflation pressure should be kept below 100
psi to avoid tire blow-off. I often read of tires inflated to
120-140psi and wonder what sort of steep, hard braking descents these
riders experience, having seen and experienced plenty of blow-offs at
100+psi on such descents. Tandems are special cases that should
always have a hub brake to make such descents safe.

Jobst Brandt



If a tyre has 100psi at 20C (68F), it need to get to about 80C (176F)
to increase the pressure to 120psi. This seems unlikely as the tyre is
cooled by conduction to the road surface. As the rim will probably
always be hotter than the tyre under braking, thermal expansion
shouldn't loosen the tyre fit either. Do you know why tyres blow off
on descents? Is there a significant difference in failure rate
depending on bead material? Does the valve stem lock the tyre to the
rim at one point and the rest of the tyre creeps round the rim due to
braking force? Just curious to know whether there is any rigorous
research into failure mode and cause.


Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary

Dear Kinky,

Oops, I forgot one point.

While we think of the pavement as cooling the tire off by conduction,
we (or at least I) tend to forget that only the contact between the
tire and the pavement is the contact patch, which is tiny in relation
to the surface and mass of the tire.

As an analogy, imagine a sweaty athlete trying to cool off on a hot
day by sliding a single ice cube over his body, or someone trying to
stay warm on a winter day by running a hot chestnut over his
epidermis.

Carl Fogel