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question about tubulars



 
 
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  #101  
Old October 29th 07, 08:58 PM posted to rec.bicycles.misc,rec.bicycles.racing
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Default question about tubulars

Dave who? writes:

It is hard to imagine a CFRP (not solely carbon [1]) rim being as
durable as one made of even a relatively soft metal such as
aluminium alloy if rim brakes are used.


[1] A pure carbon (diamond) rim would have great resistance to
brake track wear, as it would be harder than the silica grit
commonly encountered.


Diamond rims would have great wear resistance but they would be a
terrible choice for a braking surface. This is because diamond has
a very low coefficient of friction. In fact, a polished diamond
surface is slipperier than Teflon.


Could you give a reference to where you found that information. My
experience with diamond like carbon on storage disks did not show any
signs of low friction, only that the wear debris in normal atmosphere,
unlike from other coatings, is benign to the disk/head interface.


Riding with diamond wheels would be like applying a thick layer of
grease to your metal rims.


Again, please cite some material pairings and source for this
information.


Google is your friend


http://frictioncenter.siu.edu/databaseSearch.html


It would seem that Teflon is still more slippery than diamond, but not
by much.


You did notice the pairing in that table? We don't use diamond brake
pads. We need the coefficient of friction between a soft brake pad
and a diamond to make any sense of the claim.

Jobst Brandt
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  #102  
Old October 29th 07, 09:54 PM posted to rec.bicycles.misc,rec.bicycles.racing
Paul O
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Default question about tubulars

wrote:
Paul D Oosterhout writes:

It is hard to imagine a CFRP (not solely carbon [1]) rim being as
durable as one made of even a relatively soft metal such as
aluminium alloy if rim brakes are used.


[1] A pure carbon (diamond) rim would have great resistance to
brake track wear, as it would be harder than the silica grit
commonly encountered.


Diamond rims would have great wear resistance but they would be a
terrible choice for a braking surface. This is because diamond has
a very low coefficient of friction. In fact, a polished diamond
surface is slipperier than Teflon.


Could you give a reference to where you found that information. My
experience with diamond like carbon on storage disks did not show any
signs of low friction, only that the wear debris in normal atmosphere,
unlike from other coatings, is benign to the disk/head interface.

Riding with diamond wheels would be like applying a thick layer of
grease to your metal rims.


Again, please cite some material pairings and source for this
information.

Jobst Brandt


Oops, my memory has been playing tricks on me! I looked up the
coefficient of friction on several sites and diamond has a much higher
coefficient of friction than Teflon.

Diamond's static COF on metal is 0.10 to 0.15 which is about the same as
the COF for graphite. In contrast, Teflon is much slipperier with a
static COF on steel of 0.04. See:

http://www.engineershandbook.com/Tab...efficients.htm
http://www.roymech.co.uk/Useful_Tabl...o_of_frict.htm

I don't know what's happening with my mind these days. Maybe I was
thinking about diamond's thermal conductivity...

--

Paul D Oosterhout
I work for SAIC (but I don't speak for SAIC)
  #103  
Old October 29th 07, 10:21 PM posted to rec.bicycles.misc,rec.bicycles.racing
Dave
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Posts: 19
Default question about tubulars

wrote:
Dave who? writes:

It is hard to imagine a CFRP (not solely carbon [1]) rim being as
durable as one made of even a relatively soft metal such as
aluminium alloy if rim brakes are used.


[1] A pure carbon (diamond) rim would have great resistance to
brake track wear, as it would be harder than the silica grit
commonly encountered.


Diamond rims would have great wear resistance but they would be a
terrible choice for a braking surface. This is because diamond has
a very low coefficient of friction. In fact, a polished diamond
surface is slipperier than Teflon.


Could you give a reference to where you found that information. My
experience with diamond like carbon on storage disks did not show any
signs of low friction, only that the wear debris in normal atmosphere,
unlike from other coatings, is benign to the disk/head interface.


Riding with diamond wheels would be like applying a thick layer of
grease to your metal rims.


Again, please cite some material pairings and source for this
information.


Google is your friend


http://frictioncenter.siu.edu/databaseSearch.html

It would seem that Teflon is still more slippery than diamond, but not
by much.


You did notice the pairing in that table? We don't use diamond brake
pads. We need the coefficient of friction between a soft brake pad
and a diamond to make any sense of the claim.

Jobst Brandt


I read the claim as "a polished diamond surface is slipperier than
Teflon." I see no mention of diamond's relative performance with soft
brake pads. If this is the case, the table referenced seems to provide
the right comparison.

Dave
  #104  
Old October 29th 07, 10:46 PM posted to rec.bicycles.misc,rec.bicycles.racing
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Posts: 3,751
Default question about tubulars

Paul D Oosterhout writes:

It is hard to imagine a CFRP (not solely carbon [1]) rim being as
durable as one made of even a relatively soft metal such as
aluminium alloy if rim brakes are used.


[1] A pure carbon (diamond) rim would have great resistance to
brake track wear, as it would be harder than the silica grit
commonly encountered.


Diamond rims would have great wear resistance but they would be a
terrible choice for a braking surface. This is because diamond has
a very low coefficient of friction. In fact, a polished diamond
surface is slipperier than Teflon.


Could you give a reference to where you found that information. My
experience with diamond like carbon on storage disks did not show any
signs of low friction, only that the wear debris in normal atmosphere,
unlike from other coatings, is benign to the disk/head interface.


Riding with diamond wheels would be like applying a thick layer of
grease to your metal rims.


Again, please cite some material pairings and source for this
information.


Oops, my memory has been playing tricks on me! I looked up the
coefficient of friction on several sites and diamond has a much
higher coefficient of friction than Teflon.


Diamond's static COF on metal is 0.10 to 0.15 which is about the
same as the COF for graphite. In contrast, Teflon is much
slipperier with a static COF on steel of 0.04. See:


http://www.engineershandbook.com/Tab...efficients.htm
http://www.roymech.co.uk/Useful_Tabl...o_of_frict.htm

I don't know what's happening with my mind these days. Maybe I was
thinking about diamond's thermal conductivity...


Graphite is not a good comparison because its lubricity arises from
adsorbed moisture. In a vacuum, (absence of water vapor) graphite is
just so much grinding grit.

Besides, my understanding of coefficient of friction is that it is a
value for a material pair. It has little meaning for a single
material. The coefficient is derived from the number of asperity
contacts and the shear force of the weaker material. For that reason,
diamond on diamond has a low value because it has few asperity
contacts from its high modulus of elasticity.

Jobst Brandt
  #105  
Old October 30th 07, 12:32 AM posted to rec.bicycles.misc,rec.bicycles.racing
SLAVE of THE STATE
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Posts: 1,774
Default question about tubulars

On Oct 29, 2:21 pm, Dave wrote:
wrote:
Dave who? writes:


It is hard to imagine a CFRP (not solely carbon [1]) rim being as
durable as one made of even a relatively soft metal such as
aluminium alloy if rim brakes are used.


[1] A pure carbon (diamond) rim would have great resistance to
brake track wear, as it would be harder than the silica grit
commonly encountered.


Diamond rims would have great wear resistance but they would be a
terrible choice for a braking surface. This is because diamond has
a very low coefficient of friction. In fact, a polished diamond
surface is slipperier than Teflon.


Could you give a reference to where you found that information. My
experience with diamond like carbon on storage disks did not show any
signs of low friction, only that the wear debris in normal atmosphere,
unlike from other coatings, is benign to the disk/head interface.


Riding with diamond wheels would be like applying a thick layer of
grease to your metal rims.


Again, please cite some material pairings and source for this
information.


Google is your friend


http://frictioncenter.siu.edu/databaseSearch.html


It would seem that Teflon is still more slippery than diamond, but not
by much.


You did notice the pairing in that table? We don't use diamond brake
pads. We need the coefficient of friction between a soft brake pad
and a diamond to make any sense of the claim.



I read the claim as "a polished diamond surface is slipperier than
Teflon." I see no mention of diamond's relative performance with soft
brake pads. If this is the case, the table referenced seems to provide
the right comparison.


This is all quite irrelevent. Diamond is carbon and it is expensive.
Therefore it is good to have on my bike. I have a carbon diamond
frame, why not diamond carbon wheels? Would they sparkle? Who cares
how they brake? They'de be hot in a way that really matters.

  #106  
Old October 30th 07, 01:52 AM posted to rec.bicycles.racing
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Default question about tubulars

On Oct 27, 2:09 pm, "Phil Holman" piholmanc@yourservice wrote:
"Dan Connelly" wrote in message

Phil Holman wrote:


Boutique? Carbon wheels are substantially lighter for racing. Not
for training, or touring the Alpes. Who cares about 0.5% speed
advantages when you're touring or training?


Apparently quite a few riding up and down North Oracle Rd, Tucson.


Although, you're limited to the parade route since that may
be one of the few places in Tucson you could ride a pair
of carbon rims regularly without fear that the bumpy road
patches will do them in.

Ben

  #107  
Old October 30th 07, 06:32 PM posted to rec.bicycles.racing
Scott
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Posts: 1,859
Default question about tubulars

On Oct 29, 6:52 pm, "
wrote:
On Oct 27, 2:09 pm, "Phil Holman" piholmanc@yourservice wrote:

"Dan Connelly" wrote in message


Phil Holman wrote:


Boutique? Carbon wheels are substantially lighter for racing. Not
for training, or touring the Alpes. Who cares about 0.5% speed
advantages when you're touring or training?


Apparently quite a few riding up and down North Oracle Rd, Tucson.


Although, you're limited to the parade route since that may
be one of the few places in Tucson you could ride a pair
of carbon rims regularly without fear that the bumpy road
patches will do them in.

Ben


Don't you blaspheme in here! Tucson is one of the best cities in the
country for cycling, Bicycling magazine says so. I haven't been there
in far too long, but I recall all the streets being very smooth and
the drivers friendly!

 




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