Is Lennard Zinn wrogn carbon rims?

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.

"HardwareLust" writes:

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

Huh. Well now, there's an interesting point! Of course, you can
unseat a clincher if the pressure is low enough, but there's no glue
to melt.

And what's up with tubeless road tires for bikes? Given how often
shards of glass, thorns, Michelin wires, etc find their way into my
inner tubes, I want tires that can be repaired in a couple of minutes
and get on the ride again. Woodenja have to patch a tubeless tire
after every puncture (or install a tube, which seems like it defeats
whatever purpose there might be to this exercise)?

"HardwareLust" writes:

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

Huh. Well now, there's an interesting point! Of course, you can
unseat a clincher if the pressure is low enough, but there's no glue
to melt.

And what's up with tubeless road tires for bikes? Given how often
shards of glass, thorns, Michelin wires, etc find their way into my
inner tubes, I want tires that can be repaired in a couple of minutes
and get on the ride again. Woodenja have to patch a tubeless tire
after every puncture (or install a tube, which seems like it defeats
whatever purpose there might be to this exercise)?

On Fri, 23 Jul 2004 02:47:36 GMT, "HardwareLust"
wrote:

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

If you put enough side force on it to peel the bead away from the
flange, it will lose sealing and deflate...but I would expect that the
side force required to cause this to occur should be quite large, and
it's possible that it might taco the wheel first. If the tire is
underinflated, of course, peeling it becomes much easier. Fully
inflated, on a smooth unobstructed path, the tire should skid long
before it would develop enough side force to peel.

I noticed that Hutchinson's instructions for repair of their tubeless
tires basically advise just gluing the hole closed on simple
punctures, and applying an internal patch only where the breach is a
4mm (or longer) cut. They recommend using a cyanoacrylate adhesive
(Loctite 4850 to be specific) rather than the traditional type of
patch glue. I suspect this will vary from maker to maker. If so, the
procedure for repairing tubeless tires looks like it's going to be a
lot less universal than the process is for tubes.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

On Fri, 23 Jul 2004 02:47:36 GMT, "HardwareLust"
wrote:

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

If you put enough side force on it to peel the bead away from the
flange, it will lose sealing and deflate...but I would expect that the
side force required to cause this to occur should be quite large, and
it's possible that it might taco the wheel first. If the tire is
underinflated, of course, peeling it becomes much easier. Fully
inflated, on a smooth unobstructed path, the tire should skid long
before it would develop enough side force to peel.

I noticed that Hutchinson's instructions for repair of their tubeless
tires basically advise just gluing the hole closed on simple
punctures, and applying an internal patch only where the breach is a
4mm (or longer) cut. They recommend using a cyanoacrylate adhesive
(Loctite 4850 to be specific) rather than the traditional type of
patch glue. I suspect this will vary from maker to maker. If so, the
procedure for repairing tubeless tires looks like it's going to be a
lot less universal than the process is for tubes.
--
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 22:59:48 -0500, Tim McNamara
wrote:

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.

Zinn's factual conclusions have validity, but the needs of the rider
may (or may not!) outweigh them; it's his opinions, not his facts,
that I disagree with. In all forms of wheeled racing, there are
components available which provide an advantage *in racing* which
comes with drawbacks that may make these components less advantageous
for everyday non-racing use. For example, it doesn't matter to a
racer that the pads which work well with a carbon rim have a short
life; the pads can be changed at the end of the day, or even swapped
out via a bike change at the end of a stage if needed. As such,
carbon rims may be quite appropriate in that instance, while putting a
set on a touring bike that is destined to haul a rider and his gear on
a circuit of the national parks in the Rockies might necessitate the
inclusion of more sets of spare brake pads than the rider wants to
spend time replacing. "Good" and "bad" are really functions of usage
when you're speaking of components. Any of the bikes used in today's
stage of the TdF would be inappropriate as a choice for a run down a
ski slope, for instance, but that hardly makes any part of them "bad".

Oddly enough, I have met a couple of people over the years who went
out and bought an exotic bike with then-current state-of-the-art tech,
and *never wore out a single part* because they put far less than a
thousand miles on it in the entire time they owned it. In one case,
the guy made a big show of his "just like the one Greg Lemond rode
this year" roadie sitting pristine and shiny in his living room; it
had been detailed by the same service that detailed his Jag once a
week, complete with Armorall (or something like it) on the saddle. If
the chain had lube on it, I couldn't tell. To that (non)-rider, none
of the drawbacks of his bike were relevant; he wasn't actually using
it to ride, just to show off the fact that he could afford to spend a
lot of money on something that was, in effect, just a decoration.
--
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 22:59:48 -0500, Tim McNamara
wrote:

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.

Zinn's factual conclusions have validity, but the needs of the rider
may (or may not!) outweigh them; it's his opinions, not his facts,
that I disagree with. In all forms of wheeled racing, there are
components available which provide an advantage *in racing* which
comes with drawbacks that may make these components less advantageous
for everyday non-racing use. For example, it doesn't matter to a
racer that the pads which work well with a carbon rim have a short
life; the pads can be changed at the end of the day, or even swapped
out via a bike change at the end of a stage if needed. As such,
carbon rims may be quite appropriate in that instance, while putting a
set on a touring bike that is destined to haul a rider and his gear on
a circuit of the national parks in the Rockies might necessitate the
inclusion of more sets of spare brake pads than the rider wants to
spend time replacing. "Good" and "bad" are really functions of usage
when you're speaking of components. Any of the bikes used in today's
stage of the TdF would be inappropriate as a choice for a run down a
ski slope, for instance, but that hardly makes any part of them "bad".

Oddly enough, I have met a couple of people over the years who went
out and bought an exotic bike with then-current state-of-the-art tech,
and *never wore out a single part* because they put far less than a
thousand miles on it in the entire time they owned it. In one case,
the guy made a big show of his "just like the one Greg Lemond rode
this year" roadie sitting pristine and shiny in his living room; it
had been detailed by the same service that detailed his Jag once a
week, complete with Armorall (or something like it) on the saddle. If
the chain had lube on it, I couldn't tell. To that (non)-rider, none
of the drawbacks of his bike were relevant; he wasn't actually using
it to ride, just to show off the fact that he could afford to spend a
lot of money on something that was, in effect, just a decoration.
--
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 23:03:20 -0500, Tim McNamara
wrote:

And what's up with tubeless road tires for bikes? Given how often
shards of glass, thorns, Michelin wires, etc find their way into my
inner tubes, I want tires that can be repaired in a couple of minutes
and get on the ride again. Woodenja have to patch a tubeless tire
after every puncture (or install a tube, which seems like it defeats
whatever purpose there might be to this exercise)?

Tubeless tires are faster to repair in some cases. Hutchinson's
recommended procedure for small holes is "Locate the puncture, remove
debris, apply Loctite 4850, hold closed for 3 minutes, inflate and
go." Even for larger holes, it's merely a matter of peeling the tire
and applying a quick interior patch...and there is *never* a danger of
snakebiting the tube when reinstalling a tubeless.
--
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 23:03:20 -0500, Tim McNamara
wrote:

And what's up with tubeless road tires for bikes? Given how often
shards of glass, thorns, Michelin wires, etc find their way into my
inner tubes, I want tires that can be repaired in a couple of minutes
and get on the ride again. Woodenja have to patch a tubeless tire
after every puncture (or install a tube, which seems like it defeats
whatever purpose there might be to this exercise)?

Tubeless tires are faster to repair in some cases. Hutchinson's
recommended procedure for small holes is "Locate the puncture, remove
debris, apply Loctite 4850, hold closed for 3 minutes, inflate and
go." Even for larger holes, it's merely a matter of peeling the tire
and applying a quick interior patch...and there is *never* a danger of
snakebiting the tube when reinstalling a tubeless.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

On 2004-07-22 16:55:22 -0700, Tim McNamara said:

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.

Fair enough. Carbon rims don't "conduct heat well." Heat is
generated, and as such if it's not carried away it gets concentrated
"somewhere."

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?

Cork doesn't melt the same way that rubber does. I can tell you from
personal experience that "standard" rubber brake pads don't work well
with carbon pads. In fact I was riding carbon rims on a descent, and
melted the rear pad. I was going about 40 through a corner, and was
drag braking (just barely -- almost no pressure on the rear brake).
Rear wheel locked up, and I lowsided.

I had actually locked up the rear wheel 3 or 4 times previously to
this... I wasn't sure what was going on, I though perhaps someone had
put bleach on my Corsa CX's -- they were that prone to lockup.

http://www.altovelo.org/rr01/results/




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.

Because the pads are melting. Intially they are not that "grabby" but
after 3 or 4 seconds of braking, the friction coefficient goes up
significantly. It's decidedly non-linear, and that's "a bad thing."

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?

Agreed here -- the pads are going to melt and get grabby FAR before the
tubular glue will melt. However, if he was using cork pads, they
probably wouldn't have melted. It would be a pretty colossal gaffe for
a mechanic to *not* use carbon-compatible pads these days... it
wouldn't take long for it to become evident it was dangerous.

I've never actually used cork pads on CF rims (I sold the rims soon
after my crash), so I don't know how hot things would get on a long
descent with cork pads. Tons and tons of heat would be generated and
it wouldn't be conducted away very well, so it seems the braking
surface and pads would have to get awfully hot.


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!