Is Lennard Zinn wrogn carbon rims?

From http://www.velonews.com/tour2004/tec...es/6642.0.html

Carbon wheel issues

Carbon wheels are a case in point. Almost all of the riders are using
carbon wheels on mountain stages now because of the weight savings,
but braking continues to be a problem with them. Simply getting
carbon-specific pads is insufficient, because carbon is an insulator
and seeks to retain heat, while aluminum is a conductor and seeks to
dissipate it. This can cause all sorts of problems.

As I understand it, this is wrong. An insulator does not conduct
energy, which is different from "seeking to retain it." A designer
might use an insulator to retain heat by surrounding the hot stuff
with the insulator, but that works because the insulator simply
doesn't conduct heat well.

Most Tour riders are using the red Corima cork pads (see photo) on
their carbon rims, although U.S. Postal is using a special pad that
Keith Bontrager came up with. It is of the utmost importance to have
a good pad. I have descended our steep, five-mile Flagstaff Mountain
west of Boulder many times with various carbon wheels special carbon
pads, as well as standard pads. All of them, save for the ADA cork
pads (I have not used the Corima cork pads, but I assume they are
similar), wore down a huge amount with each descent. Besides the
visible reduction of the pad thickness, the pads built up a lot of
melted pad material ahead on the leading end

It seems to me that melting brake pads are not the result of the rim
getting hot from absorbing heat, but of the pad getting hot because
the rims is *not* absorbing heat. Is cork used because it has no
melting point, not being a rubber based material, and perhaps a high
vaporization point?

Braking on carbon rims tends to be grabby anyway, and the rim heating
accentuates it.

Are carbon rims grabby because they are getting hot or because of
coefficient of friction between rim and pad being too high? Or
because the brake pads are getting hot, as they retain the heat and
have no way to shed it rapidly enough, and the surface of the pad is
melting and sticking to the rim? Everything I've read about this thus
far in r.b.t suggested to me that carbon rims do not heat up, do not
conduct heat away from the brake pads, and thus the pads get hot and
melt or vaporize material. Hence the pads wear out in short order.

When there is a lot of heat with tubular wheels, there is always the
possibility of rolling tires. Even with aluminum rims, the glue gets
soft on a hot descent, and the tires visibly slip around the rim,
causing the valve stem to be angled sharply. We used to flip our
front wheel around on subsequent mountain stages so that the valve
stem would straighten back out. But the heat with a carbon can be far
more extreme. I think Joseba Beloki could have avoided his crash last
year had he not been using carbon rims. The hot rims grabbed when he
braked hard, locking his rear wheel. When the wheel came back down,
the hot glue allowed the tire to roll right off of the rim.

Again, Zinn seems to be stating that this insulator, the carbon fiber
rim, is absorbing and storing heat from braking. If the rim is hot
enough to melt brake pads, how could any glue hold on any carbon rim
when descending? The melting point of glue must be far below the
melting point of brake pads! If this is the case, then carbon rims
must be totally unsuited to this application. Or is it that the pads
get too hot and stick to the rim, since the latter does not conduct
the heat out of the pads, causing grabbing?

This year, Thomas Voeckler switched bikes a number of times on
mountain stages while wearing the yellow jersey. His director
sportif, Jean Rene Bernadeau (who won epic mountain stages a rider
himself - remember his win in Sondrio in the Giro stage over the
Passo Stelvio with Bernard Hinault in the early 1980s?), said it was
due to fear of rolling a tire, since Voeckler's carbon rims were
getting so hot.

From everything I've read about this in rec.bikes.tech, I think that
either Bernardeau and Zinn really don't understand what's going on
here- or I have totally misunderstood everything I've ever read on the
subject!

On Thu, 22 Jul 2004 18:55:22 -0500, Tim McNamara
wrote:



Are carbon rims grabby because they are getting hot or because of
coefficient of friction between rim and pad being too high?

I've got some oldish Zzip carbon rims and they are grabby all the
time.

JT

On Thu, 22 Jul 2004 18:55:22 -0500, Tim McNamara
wrote:



Are carbon rims grabby because they are getting hot or because of
coefficient of friction between rim and pad being too high?

I've got some oldish Zzip carbon rims and they are grabby all the
time.

JT

On Thu, 22 Jul 2004 18:55:22 -0500, Tim McNamara
wrote:

Are carbon rims grabby because they are getting hot or because of
coefficient of friction between rim and pad being too high? Or
because the brake pads are getting hot, as they retain the heat and
have no way to shed it rapidly enough, and the surface of the pad is
melting and sticking to the rim? Everything I've read about this thus
far in r.b.t suggested to me that carbon rims do not heat up, do not
conduct heat away from the brake pads, and thus the pads get hot and
melt or vaporize material. Hence the pads wear out in short order.

Carbon rims absorb little heat, but heat is generated by the friction
of brake operation and must go somewhere...or cause something that
dissipates it in some manner. Cork is a slipperier material than
those used in the rubber-like compounds, and will grab a carbon rim
more evenly than a conventional brake pad...but the "cork" pads are
not purely cork, they still have a resilient rubber-like component to
bond the cork particles together, and that's probably what's beading
up at the edges of the pads on descents. Using cork as a friction
material is not a new technique; it works well enough (better than
rubber in some instances, such as when the friction surface is wet
chome-plated steel) that it's been used as a component of braking
assemblies in a multitude of applications for a long time.

Carbon rims, as a class of part, are neither "good" nor "bad" per se.
They are *different* from aluminum and other materials, and those
differences need to be taken into account in the selection of
components that will be used with them. It also helps if people pay
attention to whether their riding needs mitigate in favor of a carbon
rim when making the selection, but a lot of people are going to buy
the most exotic stuff just for the snob factor regardless of any
possibility that something less esoteric might actually work better
for them. The same effect also exists in many other fields. For
example, talk to someone who deals in high-end car stereos if you want
to hear amusing tales of people showing up at a shop with a whole box
of exotic mutually incompatible items that they want installed in
their car to create what they are certain will be The Ultimate Sound
System.


--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

On Thu, 22 Jul 2004 18:55:22 -0500, Tim McNamara
wrote:

Are carbon rims grabby because they are getting hot or because of
coefficient of friction between rim and pad being too high? Or
because the brake pads are getting hot, as they retain the heat and
have no way to shed it rapidly enough, and the surface of the pad is
melting and sticking to the rim? Everything I've read about this thus
far in r.b.t suggested to me that carbon rims do not heat up, do not
conduct heat away from the brake pads, and thus the pads get hot and
melt or vaporize material. Hence the pads wear out in short order.

Carbon rims absorb little heat, but heat is generated by the friction
of brake operation and must go somewhere...or cause something that
dissipates it in some manner. Cork is a slipperier material than
those used in the rubber-like compounds, and will grab a carbon rim
more evenly than a conventional brake pad...but the "cork" pads are
not purely cork, they still have a resilient rubber-like component to
bond the cork particles together, and that's probably what's beading
up at the edges of the pads on descents. Using cork as a friction
material is not a new technique; it works well enough (better than
rubber in some instances, such as when the friction surface is wet
chome-plated steel) that it's been used as a component of braking
assemblies in a multitude of applications for a long time.

Carbon rims, as a class of part, are neither "good" nor "bad" per se.
They are *different* from aluminum and other materials, and those
differences need to be taken into account in the selection of
components that will be used with them. It also helps if people pay
attention to whether their riding needs mitigate in favor of a carbon
rim when making the selection, but a lot of people are going to buy
the most exotic stuff just for the snob factor regardless of any
possibility that something less esoteric might actually work better
for them. The same effect also exists in many other fields. For
example, talk to someone who deals in high-end car stereos if you want
to hear amusing tales of people showing up at a shop with a whole box
of exotic mutually incompatible items that they want installed in
their car to create what they are certain will be The Ultimate Sound
System.


--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

a little off topic but Lennard mentions corima and ADA pads. Any suggestions
on best carbon specific pads out there?
thanx,
andy
"Tim McNamara" wrote in message
...
From http://www.velonews.com/tour2004/tec...es/6642.0.html

Carbon wheel issues

Carbon wheels are a case in point. Almost all of the riders are using
carbon wheels on mountain stages now because of the weight savings,
but braking continues to be a problem with them. Simply getting
carbon-specific pads is insufficient, because carbon is an insulator
and seeks to retain heat, while aluminum is a conductor and seeks to
dissipate it. This can cause all sorts of problems.

As I understand it, this is wrong. An insulator does not conduct
energy, which is different from "seeking to retain it." A designer
might use an insulator to retain heat by surrounding the hot stuff
with the insulator, but that works because the insulator simply
doesn't conduct heat well.

Most Tour riders are using the red Corima cork pads (see photo) on
their carbon rims, although U.S. Postal is using a special pad that
Keith Bontrager came up with. It is of the utmost importance to have
a good pad. I have descended our steep, five-mile Flagstaff Mountain
west of Boulder many times with various carbon wheels special carbon
pads, as well as standard pads. All of them, save for the ADA cork
pads (I have not used the Corima cork pads, but I assume they are
similar), wore down a huge amount with each descent. Besides the
visible reduction of the pad thickness, the pads built up a lot of
melted pad material ahead on the leading end

It seems to me that melting brake pads are not the result of the rim
getting hot from absorbing heat, but of the pad getting hot because
the rims is *not* absorbing heat. Is cork used because it has no
melting point, not being a rubber based material, and perhaps a high
vaporization point?

Braking on carbon rims tends to be grabby anyway, and the rim heating
accentuates it.

Are carbon rims grabby because they are getting hot or because of
coefficient of friction between rim and pad being too high? Or
because the brake pads are getting hot, as they retain the heat and
have no way to shed it rapidly enough, and the surface of the pad is
melting and sticking to the rim? Everything I've read about this thus
far in r.b.t suggested to me that carbon rims do not heat up, do not
conduct heat away from the brake pads, and thus the pads get hot and
melt or vaporize material. Hence the pads wear out in short order.

When there is a lot of heat with tubular wheels, there is always the
possibility of rolling tires. Even with aluminum rims, the glue gets
soft on a hot descent, and the tires visibly slip around the rim,
causing the valve stem to be angled sharply. We used to flip our
front wheel around on subsequent mountain stages so that the valve
stem would straighten back out. But the heat with a carbon can be far
more extreme. I think Joseba Beloki could have avoided his crash last
year had he not been using carbon rims. The hot rims grabbed when he
braked hard, locking his rear wheel. When the wheel came back down,
the hot glue allowed the tire to roll right off of the rim.

Again, Zinn seems to be stating that this insulator, the carbon fiber
rim, is absorbing and storing heat from braking. If the rim is hot
enough to melt brake pads, how could any glue hold on any carbon rim
when descending? The melting point of glue must be far below the
melting point of brake pads! If this is the case, then carbon rims
must be totally unsuited to this application. Or is it that the pads
get too hot and stick to the rim, since the latter does not conduct
the heat out of the pads, causing grabbing?

This year, Thomas Voeckler switched bikes a number of times on
mountain stages while wearing the yellow jersey. His director
sportif, Jean Rene Bernadeau (who won epic mountain stages a rider
himself - remember his win in Sondrio in the Giro stage over the
Passo Stelvio with Bernard Hinault in the early 1980s?), said it was
due to fear of rolling a tire, since Voeckler's carbon rims were
getting so hot.

From everything I've read about this in rec.bikes.tech, I think that
either Bernardeau and Zinn really don't understand what's going on
here- or I have totally misunderstood everything I've ever read on the
subject!

a little off topic but Lennard mentions corima and ADA pads. Any suggestions
on best carbon specific pads out there?
thanx,
andy
"Tim McNamara" wrote in message
...
From http://www.velonews.com/tour2004/tec...es/6642.0.html

Carbon wheel issues

Carbon wheels are a case in point. Almost all of the riders are using
carbon wheels on mountain stages now because of the weight savings,
but braking continues to be a problem with them. Simply getting
carbon-specific pads is insufficient, because carbon is an insulator
and seeks to retain heat, while aluminum is a conductor and seeks to
dissipate it. This can cause all sorts of problems.

As I understand it, this is wrong. An insulator does not conduct
energy, which is different from "seeking to retain it." A designer
might use an insulator to retain heat by surrounding the hot stuff
with the insulator, but that works because the insulator simply
doesn't conduct heat well.

Most Tour riders are using the red Corima cork pads (see photo) on
their carbon rims, although U.S. Postal is using a special pad that
Keith Bontrager came up with. It is of the utmost importance to have
a good pad. I have descended our steep, five-mile Flagstaff Mountain
west of Boulder many times with various carbon wheels special carbon
pads, as well as standard pads. All of them, save for the ADA cork
pads (I have not used the Corima cork pads, but I assume they are
similar), wore down a huge amount with each descent. Besides the
visible reduction of the pad thickness, the pads built up a lot of
melted pad material ahead on the leading end

It seems to me that melting brake pads are not the result of the rim
getting hot from absorbing heat, but of the pad getting hot because
the rims is *not* absorbing heat. Is cork used because it has no
melting point, not being a rubber based material, and perhaps a high
vaporization point?

Braking on carbon rims tends to be grabby anyway, and the rim heating
accentuates it.

Are carbon rims grabby because they are getting hot or because of
coefficient of friction between rim and pad being too high? Or
because the brake pads are getting hot, as they retain the heat and
have no way to shed it rapidly enough, and the surface of the pad is
melting and sticking to the rim? Everything I've read about this thus
far in r.b.t suggested to me that carbon rims do not heat up, do not
conduct heat away from the brake pads, and thus the pads get hot and
melt or vaporize material. Hence the pads wear out in short order.

When there is a lot of heat with tubular wheels, there is always the
possibility of rolling tires. Even with aluminum rims, the glue gets
soft on a hot descent, and the tires visibly slip around the rim,
causing the valve stem to be angled sharply. We used to flip our
front wheel around on subsequent mountain stages so that the valve
stem would straighten back out. But the heat with a carbon can be far
more extreme. I think Joseba Beloki could have avoided his crash last
year had he not been using carbon rims. The hot rims grabbed when he
braked hard, locking his rear wheel. When the wheel came back down,
the hot glue allowed the tire to roll right off of the rim.

Again, Zinn seems to be stating that this insulator, the carbon fiber
rim, is absorbing and storing heat from braking. If the rim is hot
enough to melt brake pads, how could any glue hold on any carbon rim
when descending? The melting point of glue must be far below the
melting point of brake pads! If this is the case, then carbon rims
must be totally unsuited to this application. Or is it that the pads
get too hot and stick to the rim, since the latter does not conduct
the heat out of the pads, causing grabbing?

This year, Thomas Voeckler switched bikes a number of times on
mountain stages while wearing the yellow jersey. His director
sportif, Jean Rene Bernadeau (who won epic mountain stages a rider
himself - remember his win in Sondrio in the Giro stage over the
Passo Stelvio with Bernard Hinault in the early 1980s?), said it was
due to fear of rolling a tire, since Voeckler's carbon rims were
getting so hot.

From everything I've read about this in rec.bikes.tech, I think that
either Bernardeau and Zinn really don't understand what's going on
here- or I have totally misunderstood everything I've ever read on the
subject!

Tim McNamara wrote:
This year, Thomas Voeckler switched bikes a number of times on
mountain stages while wearing the yellow jersey. His director
sportif, Jean Rene Bernadeau (who won epic mountain stages a rider
himself - remember his win in Sondrio in the Giro stage over the
Passo Stelvio with Bernard Hinault in the early 1980s?), said it was
due to fear of rolling a tire, since Voeckler's carbon rims were
getting so hot.

From everything I've read about this in rec.bikes.tech, I think that
either Bernardeau and Zinn really don't understand what's going on
here- or I have totally misunderstood everything I've ever read on the
subject!

According to CN, Voeckler and the rest of Brioches La Boulongerie are/were
using Mavic Carbone SL SSC's with the new tubeless clinchers. How can you
roll a clincher??

http://www.cyclingnews.com/road/2004...=voeckler-bike

Tim McNamara wrote:
This year, Thomas Voeckler switched bikes a number of times on
mountain stages while wearing the yellow jersey. His director
sportif, Jean Rene Bernadeau (who won epic mountain stages a rider
himself - remember his win in Sondrio in the Giro stage over the
Passo Stelvio with Bernard Hinault in the early 1980s?), said it was
due to fear of rolling a tire, since Voeckler's carbon rims were
getting so hot.

From everything I've read about this in rec.bikes.tech, I think that
either Bernardeau and Zinn really don't understand what's going on
here- or I have totally misunderstood everything I've ever read on the
subject!

According to CN, Voeckler and the rest of Brioches La Boulongerie are/were
using Mavic Carbone SL SSC's with the new tubeless clinchers. How can you
roll a clincher??

http://www.cyclingnews.com/road/2004...=voeckler-bike

Werehatrack writes:

On Thu, 22 Jul 2004 18:55:22 -0500, Tim McNamara
wrote:

Are carbon rims grabby because they are getting hot or because of
coefficient of friction between rim and pad being too high? Or
because the brake pads are getting hot, as they retain the heat and
have no way to shed it rapidly enough, and the surface of the pad is
melting and sticking to the rim? Everything I've read about this
thus far in r.b.t suggested to me that carbon rims do not heat up,
do not conduct heat away from the brake pads, and thus the pads get
hot and melt or vaporize material. Hence the pads wear out in short
order.

Carbon rims absorb little heat, but heat is generated by the
friction of brake operation and must go somewhere...or cause
something that dissipates it in some manner.

So, melting away the contact surface or vaporizing it might dissipate
some of that heat, if it's not being absorbed into the rim. So- to
check my understanding of this- it sounds like you think Zinn's
analysis is incorrect.