Hard braking down hill blowouts

Ben Kaufman said:

Is it normal to have blow-outs on a road bike from prolonged hard
braking going about one mile down a steep hill or should superior
wheels and tires be able to deal with the generated heat? I have an
old Panasonic but keep the tires and tubes up to date
(Performance Bike GT2 Kevlar, rated at 105 lbs, 26TPI, which are not
the best in the world but a heck of a lot better than what my LBS
sold me. It is a 27 inch rim and I could not find any better
quality tires). But is it the tire/wheel quality at issue? I have
been thinking about getting a new bike rather than trying to upgrade
this one for a number of reasons (I don't think it's even possible
to switch to the current wheel size) but the blow-outs are my
biggest justification of expenditure to my wife.

This is a traditional problem, so much so that bicycles are prohibited
down certain roads in the Alps. Zirlerberg above Innsbruck is a
classic with six runaway escape ramps for brake failures of trucks.
The Würzen Pass from Slovenia to Austria has a long 18% grade.

Locally in the Santa Clara Valley we have several tire blow-off
descents on Metcalf Road and Hicks and Almaden Roads, each of which
has had fatalities on descents. Tandems are noted for this problem,
especially if the driver isn't careful to use front and rear brakes
equally. For this reason tandems used for mountain touring are best
equipped with hub brakes (drums or disks).

In the days of tubular tires, that were glued onto rims, glue melted
allowing tires to creep and tear off the inflation stem causing rapid
deflation. I experienced that effect in the alps ans later had
clincher blow-offs on the same stretch of the Gotthard Pass.

I instrumented a wheel with pressure sensor and temperature
thermocouple to monitor a blow-off but was unsuccessful getting the
tire to separate even though temperature reached 150 degC and pressure
125 psi. The mechanism for blow-off is still unclear but it seams the
bead material softens and creeps of the hooked bead of the rim.

On steep descents after riding through water, I have generated steam
that came hissing out of the rim from around the stem as I braked for
successive hairpin turns on the Nufenen Pass in the Alps.

Jobst Brandt

Zirlerberg:

http://www.sagen.at/texte/gegenwart/oesterreich/tirol/allgemein/picknickamzirlerberg.htm

Jobst Brandt

Quoted message said:

In the days of tubular tires, that were glued onto rims, glue melted
allowing tires to creep and tear off the inflation stem causing rapid
deflation.  I experienced that effect in the alps ans later had
clincher blow-offs on the same stretch of the Gotthard Pass.

Not to dispute or anything, but where was that?
Down the south side of the old Tremola, perhaps?

Sergio
Pisa

Ben Kaufman said:

Is it normal to have blow-outs on a road bike from prolonged hard
braking going about one mile down a steep hill or should superior
wheels and tires be able to deal with the generated heat? I have an
old panasonic but keep the tires and tubes up to date (PerfomanceBike
GT2 Kevlar, rated at 105 lbs, 26TPI, which are not the best in the
world but a heck of a lot better than what my LBS sold me. It is a
27 inch rim and I could not find any better quality tires). But is it
the tire/wheel quality at issue? I have been thinking about getting a
new bike rather than trying to upgrade this one for a number of
reasons (I don't think it's even possible to switch to the current
wheel size) but the blow-outs are my biggest justification of
expenditure to my wife.

Some math I did earlier:

http://groups.google.co.uk/group/uk.rec.cycling/msg/991d32532f671264

It's probably all wrong off course, but my tentative conclusion from it
is that the rims act as heat sinks-- they can soak up quite a lot of
energy, enough for most purposes, but they can't really cope with
sustained braking.

Disks on the other hand have much less heat capacity (because they're
smaller) and probably work hotter, so I reckon they might get up to
temperature quite quickly and then dissipate more because of the bigger
temperature difference with the surrounding air. This would mean they
should be better for continuous braking. In any case they won't make the
tyres pop off.

Ben C said:

Disks on the other hand have much less heat capacity

Nor do they exchannge heat with the tyre.

Sergio
Pisa

sergio said:

Ben C said:

Disks on the other hand have much less heat capacity

Nor do they exchannge heat with the tyre.

Indeed. I wonder if they ever melt the grease in the hub though.

Sergio Servadio said:

Quoted message said:

In the days of tubular tires, that were glued onto rims, glue
melted allowing tires to creep and tear off the inflation stem
causing rapid deflation.  I experienced that effect in the alps ans
later had clincher blow-offs on the same stretch of the Gotthard
Pass.

Quoted message said:

Not to dispute or anything, but where was that? Down the south side
of the old Tremola, perhaps?

Yes, on the last hairpin turn leading to the Fortezza.

Jobst Brandt

Ben C? said:

Quoted message said:

Quoted message said:

Disks on the other hand have much less heat capacity

Quoted message said:

Quoted message said:

Nor do they exchange heat with the tyre.

Quoted message said:

Indeed. I wonder if they ever melt the grease in the hub though.

Most bicycle disks are mounted on support spiders so flimsy that heat
conduction to the bearings is insignificant.

Jobst Brandt

Quoted message said:

Ben C? said:

Quoted message said:

> Disks on the other hand have much less heat capacity

Quoted message said:

Quoted message said:

Nor do they exchange heat with the tyre.

Quoted message said:

Indeed. I wonder if they ever melt the grease in the hub though.

Most bicycle disks are mounted on support spiders so flimsy that heat
conduction to the bearings is insignificant.

"flimsy"??? is that stanford parlance for "stainless [disk] steel is a
poor conductor"? or is it presumptive nonsense from someone that
doesn't know what they're talking about?

Ben C said:

Ben Kaufman said:

Is it normal to have blow-outs on a road bike from prolonged hard
braking going about one mile down a steep hill or should superior
wheels and tires be able to deal with the generated heat? I have an
old panasonic but keep the tires and tubes up to date (PerfomanceBike
GT2 Kevlar, rated at 105 lbs, 26TPI, which are not the best in the
world but a heck of a lot better than what my LBS sold me. It is a
27 inch rim and I could not find any better quality tires). But is it
the tire/wheel quality at issue? I have been thinking about getting a
new bike rather than trying to upgrade this one for a number of
reasons (I don't think it's even possible to switch to the current
wheel size) but the blow-outs are my biggest justification of
expenditure to my wife.

Some math I did earlier:

http://groups.google.co.uk/group/uk.rec.cycling/msg/991d32532f671264

It's probably all wrong off course, but my tentative conclusion from it
is that the rims act as heat sinks-- they can soak up quite a lot of
energy, enough for most purposes, but they can't really cope with
sustained braking.

Disks on the other hand have much less heat capacity (because they're
smaller) and probably work hotter, so I reckon they might get up to
temperature quite quickly and then dissipate more because of the bigger
temperature difference with the surrounding air. This would mean they
should be better for continuous braking. In any case they won't make the
tyres pop off.

Disk brakes have their own problems with heat and can 'fade' (fail) on
long downhill sections.

From hayes...

"Brake Fluid Fade - This type of fade occurs when the brake fluid
inside a hydraulic caliper boils. An important characteristic of
brake fluid is that it is incompressible. When a brake fluid boils,
gas is formed within the system that is compressible and any lever
stroke available goes toward compressing the gas instead of generating
brake power. Interestingly enough, when a fluid is under pressure, it
is very difficult for the fluid to boil. If a brake system is under
pressure, the fluid temperature can rise above the boiling temperature
without the fluid actually boiling. Once the pressure is released,
the fluid will instantly boil and fade will occur."

A common practice for long downhill sections when using disk brakes is
to brake hard and release as opposed to constant braking to control
speed. The idea being, that when you release you allow the disk to
cool slighty.

I've experienced disk brake fade more often than rim brake blow outs
and that the disk brake fade occurs quicker during a descent than a
rim brake blow out. But, the offroad trails I ride are on average alot
steeper than the roads I ride and also require alot more braking.

Laters,

Marz

jim beam said:

Quoted message said:

Ben C? wrote:

Quoted message said:

Quoted message said:

>> Disks on the other hand have much less heat capacity

Quoted message said:

Quoted message said:

> Nor do they exchange heat with the tyre.

Quoted message said:

Quoted message said:

Indeed.  I wonder if they ever melt the grease in the hub though.

Quoted message said:

Most bicycle disks are mounted on support spiders so flimsy that heat
conduction to the bearings is insignificant.

"flimsy"???  is that stanford parlance for "stainless [disk] steel is a
poor conductor"?  or is it presumptive nonsense from someone that
doesn't know what they're talking about?

Disks are very flimsy and are not constructed to resist side to side
forces. They're only 'stiff' in the direction of the rotating wheel.
And not all disks are contructed with stainless steel spiders (see
Hope).

For example you could poor water on a hot rim to cool it, but the same
action on a disk may (and has for me) warp the bloody thing.

laters,

Marz

Ben Kaufman said:

Is it normal to have blow-outs on a road bike from prolonged hard braking going
about one mile down a steep hill or should superior wheels and tires be able
to deal with the generated heat? I have an old panasonic but keep the tires and
tubes up to date (PerfomanceBike GT2 Kevlar, rated at 105 lbs, 26TPI, which are
not the best in the world but a heck of a lot better than what my LBS sold me.
It is a 27 inch rim and I could not find any better quality tires). But is it
the tire/wheel quality at issue? I have been thinking about getting a new bike
rather than trying to upgrade this one for a number of reasons (I don't think
it's even possible to switch to the current wheel size) but the blow-outs are
my biggest justification of expenditure to my wife.

Actual blow outs or is the tire moving on the rim and tearing the stem?

Just asking because the latter is more common but the former more often blamed.

Marz said:

Ben C said:

On 2008-03-28, Ben Kaufman <[email hidden]> wrote:

Quoted message said:

Quoted message said:

Is it normal to have blow-outs on a road bike from prolonged hard
braking going about one mile down  a  steep hill  or should superior
wheels and tires be able to deal with the generated heat?  I have an
old panasonic but keep the tires and tubes up to date (PerfomanceBike
GT2 Kevlar, rated at 105 lbs, 26TPI,  which are not the best in the
world but  a heck of a lot better than what my LBS sold me. It is a
27 inch rim and I could not find any better quality tires).  But is it
the tire/wheel quality at issue?  I have been thinking about gettinga
new bike rather than trying to  upgrade this one for a number of
reasons (I don't think it's even possible to switch to the current
wheel size) but  the blow-outs are my biggest justification of
expenditure to my wife.

Quoted message said:

Some math I did earlier:

Quoted message said:

http://groups.google.co.uk/group/uk.rec.cycling/msg/991d32532f671264

Quoted message said:

It's probably all wrong off course, but my tentative conclusion from it
is that the rims act as heat sinks-- they can soak up quite a lot of
energy, enough for most purposes, but they can't really cope with
sustained braking.

Quoted message said:

Disks on the other hand have much less heat capacity (because they're
smaller) and probably work hotter, so I reckon they might get up to
temperature quite quickly and then dissipate more because of the bigger
temperature difference with the surrounding air. This would mean they
should be better for continuous braking. In any case they won't make the
tyres pop off.

Disk brakes have their own problems with heat and can 'fade' (fail) on
long downhill sections.

From hayes...

"Brake Fluid Fade - This type of fade occurs when the brake fluid
inside a hydraulic caliper boils.  An important characteristic of
brake fluid is that it is incompressible.  When a brake fluid boils,
gas is formed within the system that is compressible and any lever
stroke available goes toward compressing the gas instead of generating
brake power.  Interestingly enough, when a fluid is under pressure, it
is very difficult for the fluid to boil.  If a brake system is under
pressure, the fluid temperature can rise above the boiling temperature
without the fluid actually boiling.  Once the pressure is released,
the fluid will instantly boil and fade will occur."

A common practice for long downhill sections when using disk brakes is
to brake hard and release as opposed to constant braking to control
speed. The idea being, that when you release you allow the disk to
cool slighty.

I've experienced disk brake fade more often than rim brake blow outs
and that the disk brake fade occurs quicker during a descent than a
rim brake blow out. But, the offroad trails I ride are on average alot
steeper than the roads I ride and also require alot more braking.

I think that is an important point -- road versus trail. I have done
long road descents on my mechanical disk equiped cross bike without
any brake fade. In fact, in the rain, the disks are far better than
my rim brakes. There is a local 14 mile descent that I did in the
rain/snow on my cross bike with good stopping all the way to the
bottom -- which was a good thing because my hands were frozen, and I
couldn't generate much force on my levers. -- Jay Beattie.

Hobbes@spnb&s.com said:

Actual blow outs or is the tire moving on the rim and tearing the stem?

It certainly depends on whether one has clinchers or tubular tyres.

Sergio
Pisa

Quoted message said:

I instrumented a wheel with pressure sensor and temperature
thermocouple to monitor a blow-off but was unsuccessful getting the
tire to separate even though temperature reached 150 degC and pressure
125 psi.  The mechanism for blow-off is still unclear but it seams the
bead material softens and creeps of the hooked bead of the rim.

Some people, more successful than you (by report) (ha ha) (sorry, that
one kinda just popped out) in getting tires to blow off, use the
advantage of starting with much higher pressures. "I run 140". Yo!
Obeying the advertising...

At some point, I saw HED warning against use of a certain tire brand.
Seemed to imply that prolonged braking might not be entirely necessary
to provoke a blowoff.

Since I had some of each in the fleet, I looked at a Specialized/HED
Trispoke rim and a (IMS) Brand C tire. I noticed the bead was much too
large to fit all the way, so to speak, into the hooked bead area in
the rim.

"Already on the way out?" when inflated-- or was that over-inflated? A
nice, rounded slope on the tire bead, not much to hook into there.

Other tires, with much smaller beads, seemed to fit nicely, with the
rim perhaps (no x-ray machine on the premises) finding purchase where
the bead stops and the sidewall begins, as would seem to be the intent
of the design. --D-y

Marz said:

Ben C said:

On 2008-03-28, Ben Kaufman <[email hidden]> wrote:

[...]

Quoted message said:

Disk brakes have their own problems with heat and can 'fade' (fail) on
long downhill sections.

From hayes...

"Brake Fluid Fade - This type of fade occurs when the brake fluid
inside a hydraulic caliper boils. An important characteristic of
brake fluid is that it is incompressible. When a brake fluid boils,
gas is formed within the system that is compressible and any lever
stroke available goes toward compressing the gas instead of generating
brake power. Interestingly enough, when a fluid is under pressure, it
is very difficult for the fluid to boil. If a brake system is under
pressure, the fluid temperature can rise above the boiling temperature
without the fluid actually boiling. Once the pressure is released,
the fluid will instantly boil and fade will occur."

A common practice for long downhill sections when using disk brakes is
to brake hard and release as opposed to constant braking to control
speed. The idea being, that when you release you allow the disk to
cool slighty.

I've experienced disk brake fade more often than rim brake blow outs
and that the disk brake fade occurs quicker during a descent than a
rim brake blow out. But, the offroad trails I ride are on average alot
steeper than the roads I ride and also require alot more braking.

I have heard of fluid fade affecting bicycle brakes before. It is
shocking in my opinion because that's the easiest kind of fade to fix--
you just need brake fluid that doesn't boil, which exists. There's no
tradeoff or anything, it's a win-win no-brainer. Cars haven't suffered
from fluid fade for years with modern decent brake fluid.

I mentioned this before and someone said it's because bicycle brakes use
crappy brake fluid because it doesn't strip the paint. My advice: use
proper car brake fluid in your bike brakes but pour it in carefully and
don't spill it.

Ben C <[email hidden]> wrote in
news:[email hidden]:

Quoted message said:

I have heard of fluid fade affecting bicycle brakes before. It is
shocking in my opinion because that's the easiest kind of fade to
fix-- you just need brake fluid that doesn't boil, which exists.
There's no tradeoff or anything, it's a win-win no-brainer. Cars
haven't suffered from fluid fade for years with modern decent brake
fluid.

I mentioned this before and someone said it's because bicycle brakes
use crappy brake fluid because it doesn't strip the paint. My advice:
use proper car brake fluid in your bike brakes but pour it in
carefully and don't spill it.

Many (probably most) hydraulic disc brakes for bikes use DOT 3 or 4 brake
fluids. The problem still exists, especially if there is water in the
system. Also, one should never put DOT fluid in a system designed for
mineral oil and vice versa. The seals may not be compatible. All this said,
I've never had any problems on my mountain bike equipped with hydraulic
brakes.

--
Larry Dickman <[email hidden]>

[email hidden] wrote in news:47ec8385$0$36349
[email hidden]:

Quoted message said:

I instrumented a wheel with pressure sensor and temperature
thermocouple to monitor a blow-off but was unsuccessful getting the
tire to separate even though temperature reached 150 degC and pressure
125 psi. The mechanism for blow-off is still unclear but it seams the
bead material softens and creeps of the hooked bead of the rim.

On steep descents after riding through water, I have generated steam
that came hissing out of the rim from around the stem as I braked for
successive hairpin turns on the Nufenen Pass in the Alps.

A good reason to not use plastic rim strips. I've had these red plastic rim
strips extrude into the spoke holes causing the tube to rupture.

--
Larry Dickman <[email hidden]>

Jay Beattie said:

Marz said:

On Mar 28, 3:49 am, Ben C <[email hidden]> wrote:

Quoted message said:

Quoted message said:

On 2008-03-28, Ben Kaufman <[email hidden]> wrote:

Quoted message said:

Quoted message said:

> Is it normal to have blow-outs on a road bike from prolonged hard
> braking going about one mile down a steep hill or should superior
> wheels and tires be able to deal with the generated heat? I have an
> old panasonic but keep the tires and tubes up to date (PerfomanceBike
> GT2 Kevlar, rated at 105 lbs, 26TPI, which are not the best in the
> world but a heck of a lot better than what my LBS sold me. It is a
> 27 inch rim and I could not find any better quality tires). But is it
> the tire/wheel quality at issue? I have been thinking about getting a
> new bike rather than trying to upgrade this one for a number of
> reasons (I don't think it's even possible to switch to the current
> wheel size) but the blow-outs are my biggest justification of
> expenditure to my wife.

Quoted message said:

Quoted message said:

Some math I did earlier:

Quoted message said:

Quoted message said:

http://groups.google.co.uk/group/uk.rec.cycling/msg/991d32532f671264

Quoted message said:

Quoted message said:

It's probably all wrong off course, but my tentative conclusion from it
is that the rims act as heat sinks-- they can soak up quite a lot of
energy, enough for most purposes, but they can't really cope with
sustained braking.

Quoted message said:

Quoted message said:

Disks on the other hand have much less heat capacity (because they're
smaller) and probably work hotter, so I reckon they might get up to
temperature quite quickly and then dissipate more because of the bigger
temperature difference with the surrounding air. This would mean they
should be better for continuous braking. In any case they won't make the
tyres pop off.

Quoted message said:

Disk brakes have their own problems with heat and can 'fade' (fail) on
long downhill sections.

Quoted message said:

From hayes...

Quoted message said:

"Brake Fluid Fade - This type of fade occurs when the brake fluid
inside a hydraulic caliper boils. An important characteristic of
brake fluid is that it is incompressible. When a brake fluid boils,
gas is formed within the system that is compressible and any lever
stroke available goes toward compressing the gas instead of generating
brake power. Interestingly enough, when a fluid is under pressure, it
is very difficult for the fluid to boil. If a brake system is under
pressure, the fluid temperature can rise above the boiling temperature
without the fluid actually boiling. Once the pressure is released,
the fluid will instantly boil and fade will occur."

Quoted message said:

A common practice for long downhill sections when using disk brakes is
to brake hard and release as opposed to constant braking to control
speed. The idea being, that when you release you allow the disk to
cool slighty.

Quoted message said:

I've experienced disk brake fade more often than rim brake blow outs
and that the disk brake fade occurs quicker during a descent than a
rim brake blow out. But, the offroad trails I ride are on average alot
steeper than the roads I ride and also require alot more braking.

I think that is an important point -- road versus trail. I have done
long road descents on my mechanical disk equiped cross bike without
any brake fade.

Well, yeah - if it's mechanical, the fluid definitely won't boil!