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#101
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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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#103
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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
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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
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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
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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
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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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