Results 1 to 17 of 17
  1. #1
    Just some dude.
    Reputation:
    Join Date
    Jan 2004
    Posts
    44

    Ceramic coated discs?

    I'm sure someone has already thought of this (although I didn't find anything in the archives), but it seems to me that a ceramic coated aluminum rotor would be pretty darn cool. You'd have the lightness of an aluminum rotor, but the foul conditions durability of a stainless one (or maybe even better than stainless?). I realize there'd be issues with rocks chipping the coating, but I'd venture to guess they'd be less likely to chip than a ceramic rim. Also, you probably wouldn't be able to true them if they got bent and special pads might be required. Aside from all of that, has anyone here seen/heard of such an animal? Opinions?

  2. #2
    mmm, carbon
    Reputation:
    Join Date
    Jan 2004
    Posts
    138
    I might be way off base here, but would a ceramic coating not tend to reflect heat? -- exactly what you don't want in a disc rotor.

  3. #3
    Just some dude.
    Reputation:
    Join Date
    Jan 2004
    Posts
    44

    A brake is a brake...

    It might be missing your point, so forgive me if that's the case. It doesn't matter if it's a disc or a rim brake, you're converting kinetic energy into heat. The braking performace of a ceramic coated rim is certainly superior to a non-coated rim so it seems logical to me that a ceramic coated rotor would offer some advantage over a non-coated one. I suppose if it was a hydraulic system the low thermal conductivity of the ceramic would cause the fluid to heat up more quickly. Ah, maybe I'm starting to understand what you're saying.

  4. #4
    mmm, carbon
    Reputation:
    Join Date
    Jan 2004
    Posts
    138
    Yes, in a hydraulic system the heat sinking properties of the rotor go a long way to postponing brake overheat.

  5. #5
    The Dude Abides
    Reputation: UP Dude's Avatar
    Join Date
    Feb 2004
    Posts
    212

    I'll bet its coming

    With Porsche and Mercedes coming out with ceramic brake rotors for autos, I'd imagine we can expect to see some kind of ceramic brake system in the mountain bike world eventually. It could be a while since Porsche just introduced it last year. But with disc brake tech competition really heating up (Hayes vs. Shimano vs. Hope), we could very well see some cool stuff in the next few years.
    Until then, check this stuff out. This could be applied to a product much sooner, and could make some serious improvements. Composites are the future dude.
    .
    http://www.3m.com/market/industrial/...Brochure_3.pdf

    Imagine, ceramic discs clamped down with ceramic reinforced calipers. Mmmm, yummy. And they've demonstrated ceramic reinforced crank arms as well. Watch out for this stuff, it will be all our our bikes very soon.

  6. #6
    www.derbyrims.com
    Reputation: derby's Avatar
    Join Date
    Jan 2004
    Posts
    6,788

    No advantage with disc

    Quote Originally Posted by Tony Montana
    I'm sure someone has already thought of this (although I didn't find anything in the archives), but it seems to me that a ceramic coated aluminum rotor would be pretty darn cool. You'd have the lightness of an aluminum rotor, but the foul conditions durability of a stainless one (or maybe even better than stainless?). I realize there'd be issues with rocks chipping the coating, but I'd venture to guess they'd be less likely to chip than a ceramic rim. Also, you probably wouldn't be able to true them if they got bent and special pads might be required. Aside from all of that, has anyone here seen/heard of such an animal? Opinions?
    Since worn out rims requires lacing up a new rims it makes economic sense to get longer life using ceramic rims, even though ceramic rim braking performance isn't quite as good after broken in as metal surface rims. But disc rotors are relatively cheep and very easy to replace. I see no advantage for ceramic rotors.

    - ray

  7. #7
    Just some dude.
    Reputation:
    Join Date
    Jan 2004
    Posts
    44

    Interesting

    Having never ridden ceramic rims, I cannot comment first hand on their relative braking power vs. uncoated aluminum rims. However, I have heard several people (on the old brake forum and in person) say that their braking power is superior to regular rims and even some that say it approaches disk brake performance. You have a very different opinion on them, which would negate part of my reasoning for ceramic coated discs being so cool.

    On the other hand though, you say that rotors are relatively cheap and easy to replace. I'd agree with you regarding stainless steel rotors, but I was proposing ceramic coated aluminum rotors. Stan's aluminum rotors are $75 each.

    My idea was to combine the light weight of aluminum (54grams for a Stan's 165mm rotor plus the weight of the ceramic coating) with the durability of stainless (Stan says his aluminum rotors last 1-2 years under race conditions).

  8. #8
    Baliw
    Reputation:
    Join Date
    Jan 2004
    Posts
    203
    Quote Originally Posted by Tony Montana
    On the other hand though, you say that rotors are relatively cheap and easy to replace. I'd agree with you regarding stainless steel rotors, but I was proposing ceramic coated aluminum rotors. Stan's aluminum rotors are $75 each.

    My idea was to combine the light weight of aluminum (54grams for a Stan's 165mm rotor plus the weight of the ceramic coating) with the durability of stainless (Stan says his aluminum rotors last 1-2 years under race conditions).
    Stan also thinks there is a sucker born every minute. His figure of 1-2 years is nonsense since it's the mileage that matters. I can park his rotors for 10 years in a garage and not have it wear out at all. It's a BAD, BAD idea to use aluminum rotors since these are excellent conductors of heat (ie overheats much quicker) and have very poor durability (why do you think all automobile discs are iron/steel?).

    I think your ceramic rotor is a solution looking for a problem.

  9. #9
    mmm, carbon
    Reputation:
    Join Date
    Jan 2004
    Posts
    138
    Quote Originally Posted by Juramentado
    It's a BAD, BAD idea to use aluminum rotors since these are excellent conductors of heat (ie overheats much quicker)
    That's exactly what you want. Heat generated in braking has to go somewhere. It's much better for it to be absorbed by the rotor than by the caliper (and thus fluid).

  10. #10
    Baliw
    Reputation:
    Join Date
    Jan 2004
    Posts
    203
    Quote Originally Posted by Timbo
    That's exactly what you want. Heat generated in braking has to go somewhere. It's much better for it to be absorbed by the rotor than by the caliper (and thus fluid).
    The problem is that the rotor has such a small volume (and hence surface area for heat dissipation) that the rapid heat buildup results in very high temperatures. Aluminum is the wrong metal for this since Al alloys have much lower melting temperatures than steel, and their properties rapidly deteriorate with heat. Consider Al rims, on the other hand, where rim braking doesn't cause as rapid heat buildup as in disc rotors due to the greater volume of metal (and surface area for heat dissipation).

  11. #11
    Doesntplaywellwithmorons!
    Reputation: DeeEight's Avatar
    Join Date
    Jan 2004
    Posts
    10,581
    Quote Originally Posted by Juramentado
    The problem is that the rotor has such a small volume (and hence surface area for heat dissipation) that the rapid heat buildup results in very high temperatures. Aluminum is the wrong metal for this since Al alloys have much lower melting temperatures than steel, and their properties rapidly deteriorate with heat. Consider Al rims, on the other hand, where rim braking doesn't cause as rapid heat buildup as in disc rotors due to the greater volume of metal (and surface area for heat dissipation).
    You really need to learn your material properties better.

    The thermal conductivity of aluminium works BOTH ways. It conducts heat from the braking quickly, and then conducts it into the ambient atmosphere just as quickly.

    Aluminium rims get EQUALLY hot from braking duties. You obviously never touched a rim surface after a DH race from the late 80s/early 90s when rim brakes were basically all that folks used. It wasn't unusual to blow tubes from the heat raising the pressure inside the tube after a long run with lots of heavy braking sections.

    As to the disc rotors, a company in canada is offering MMC disc rotors for bicycles now.

    As to cars, they use cast iron rotors for the most part because of strength, cost, and cast iron conducts heat better than stainless steel. Bicycles only started using stainless steel because it doesn't rust and it was cheaper than aluminium discs (which were quite common in the early 90s on bicycle disc brakes). Rust is a problem with automobile disc rotors but as long as you drive a car often, and don't allow the rust to build up and sit on the rotors for long, it never gets thick enough to be a problem. However leave a car sitting for a few months and you can expect to find the rotors covered with rust. Bicycles can often sit for days or months without being used (especially over the winter) and rust on the
    already thin rotors would be a problem.
    Last edited by DeeEight; 03-11-2004 at 02:44 AM.

  12. #12
    Baliw
    Reputation:
    Join Date
    Jan 2004
    Posts
    203
    Quote Originally Posted by DeeEight
    You really need to learn your material properties better.
    The thermal conductivity of aluminium works BOTH ways. It conducts heat from the braking quickly, and then conducts it into the ambient atmosphere just as quickly.
    You need to learn your physics. Heat dissipation not only works through thermal coefficients but mostly on SURFACE AREA and the cooling medium. Rotors ABSORB frictional heat from pads and hopefully dissipate it quickly enough. The rate of cooling is determined mostly by radiation and convection of the heat through air around the rotor, not the aluminum. This is why surface area is crucial, and why you see fins on many heat-critical parts of heat engines such as radiators.

    Quote Originally Posted by DeeEight
    Aluminium rims get EQUALLY hot from braking duties. You obviously never touched a rim surface after a DH race from the late 80s/early 90s when rim brakes were basically all that folks used. It wasn't unusual to blow tubes from the heat raising the pressure inside the tube after a long run with lots of heavy braking sections.
    Read my post carefully before you type off. Never did I state that rims don't get as hot. Rather, it's the RATE OF HEAT BUILDUP that is different from rotors, since rims have greater volume and surface area for heat dissipation. That is, rims heat up less quickly than disc rotors do for the same amount of braking. This RATE is significant because a lower rate of heat buildup obviously allows lower temperatures and less requirement for rapid cooling when the brake is not in use.

    Quote Originally Posted by DeeEight
    As to the disc rotors, a company in canada is offering MMC disc rotors for bicycles now.
    So? That doesn't say anything about the efficacy of such. Metal matrix composites have been around for a long time, but to use these in disc rotors is solving a problem that doesn't exist. Besides, how much are these compared to SS rotors, and what do you gain for the privilege?

    Quote Originally Posted by DeeEight
    As to cars, they use cast iron rotors for the most part because of strength, cost, and cast iron conducts heat better than stainless steel. Bicycles only started using stainless steel because it doesn't rust and it was cheaper than aluminium discs (which were quite common in the early 90s on bicycle disc brakes).
    The argument isn't about cast iron vs steel, it's about aluminum vs steel or iron. Why do you think aluminum isn't used on automobiles?
    Last edited by Juramentado; 03-11-2004 at 01:59 PM. Reason: minor correction

  13. #13
    The Dude Abides
    Reputation: UP Dude's Avatar
    Join Date
    Feb 2004
    Posts
    212

    The Skinny on Material Properties

    So it seems there is some disagreement over rotor materials and why they do what they do. I'm here to offer what I know. I won't say I'm 100% right, but I think it's pretty close. For my credibility, I'm a mechanical engineering student and self-proclaimed bike geek with several materials classes under my belt. One of my close friends is also a bike geek and a material science major, so we live for this stuff.

    So when we left off, I believe it was left as "aluminum vs. steel or iron."
    Everyone knows that stainless steel is what rotors are made of now. But why? Well they're stainless so they has some degree of corrosion protection. It transfers heat moderately well and can absorb a fair amount. This is fine because steel has a high melting point and can operate at elevated temps. Not to mention its cheap and readily available. The only drawback is that it is a little on the heavy side. The lightest rotors are in the 140g range. And if you know anything about iron and cast iron rotors for cars, it should be pretty clear why they aren't used on bikes.

    So there's the standand, now lets look at alternatives:
    Aluminum - Everything about aluminum looks great; light, moves heat like no other and gets rid of it quick. However, aluminum melts at less than half the temp of steel, leading to a loss in strength and very likely warped rotors. Aluminum isn't tough either, and rotors would wear out and need replacement much sooner than we'd like.

    No one has mentioned titanium yet, which kind of surprised me since it is the precious metal of the biking world and everyone lusts for it. But maybe people already know it would make for crappy rotors? Titanium is one of the best metallic insulators, transferring about half of what stainless steel does. So half of the heat that was dissipated in your rotors would then go into your calipers, heating up the fluid, and causing trouble. To their credit, you could probably go 5 years or more on one disc. And if you're up on your new products, you've seen the new Hope MonoTi6 brakes with titanium pistons to help prevent fluid heating. Pretty cool stuff (lame pun, I know).

    Another metal I hadn't thought about until today was magnesium. It's a lot like aluminum as far as weight and the ability to move heat. The major difference is its ability to hold heat, more than ten times what aluminum can hold. I don't know exactly what heat capacity is (can anyone tell me?) but I'm guessing the higher the value, the better a metal performs at elevated temps. However just like aluminum, it has a low melting temp and would probably deform under extreme conditions.

    So that takes care of your basic alloys. Steel comes out the clear victor in that one. But the new up and coming challengers are composite materials. There are three categories of composites that work in braking applications; carbon fiber, aluminum or titanium metal matrix, and ceramics.

    Carbon fiber brakes (rotors and pads) have been used on formula one cars for a few decades now. I don't know exactly what the performance numbers are on them, but if formula one is using them, chances are its the best. The only problem, they wear out quick. Really quick. New rotors and pads go on every 800km, about 5% the life of a standard car brake system. They take 3 months to manufacture, so you better believe they are gonna cost a rediculous amount of money. (www.mclaren.co.uk)

    Metal matrix composites are really cool. They can do amazing things to the mechanical properties of the standard metal, and I would expect to see MMC's infiltrating the bike world very soon (my guess is in a Shimano crank first). However the ceramic particulates don't do much for the thermal properties of the original metal they're added to. So the thermal issues with aluminum and titanium are still there.

    That leaves us with ceramics. Ceramics have been gaining steam lately, having ceramic coatings on rims and the introduction of ceramic rotors (made of a silicon carbide matrix with chopped carbon fibers) on high-end cars. What makes them so good? They're light, really light. Less than half the weight of iron automotive rotors. They have a very high thremal conductivity coefficient, almost the same as aluminum, but have the melting point of steel. And when they heat up, they have viturally no performance fade.
    There are two drawbacks; getting rid of all the heat they absorb and brittleness. Porsche collects air from the front and moves it to the rotors to cool them off, as well as having wheels that are designed like fan blades to pull air inside. Since bike rotors are exposed, cooling would be less of an issue. I have a feeling ductility would be the major concern. Ceramics are very brittle, and traditionally would not be able to handle the sharp impacts associated with mtn biking. Granted you aren't supposed to whack your brakes, but wipe outs do happen, and it would suck a lot if you ate it and got up to find your rotors smashed to pieces. The new rotors do have the carbon fiber particulates in them, but I can't say whether or not that would help impact absorbtion. If they could work, I think a rotor in the 90g range would be very reasonable, if not lighter. For most people, 100g savings isn't worth the cost. But we all know the weight weenies and techno geeks (myself included :-) would be all over it.

    So thats what I know about material properties pertaining to brakes. If you know I was wrong somewhere, please do post a correction. My information comes from the material properties listed at http://www.matweb.com, material property and heat transfer classes at Michigan Tech, and a crazy obsession with bicycle engineering. As far as real products go, I feel that for pure technological advnacement, Hope's Mono6Ti calipers and the Shimano XTR discs are the best out there. But if I were to gamble, I'd say ceramic rotors are the next big thing in mtn bike brakes. But thats just my opinion, what do you think?

    Thanks for reading, hope you enjoyed it. Happy Trails

  14. #14
    Baliw
    Reputation:
    Join Date
    Jan 2004
    Posts
    203
    Quote Originally Posted by UP Dude
    Titanium is one of the best metallic insulators, transferring about half of what stainless steel does. So half of the heat that was dissipated in your rotors would then go into your calipers, heating up the fluid, and causing trouble.
    Not quite right. It's inaccurate to say "half of the heat that was dissipated in your rotors would then go into your calipers" for Ti. The same amount of heat won't dissipate in Ti rotors as would in SS rotors because of the lower thermal conductivity of Ti. That is, less heat is absorbed by Ti rotors in the first place. Therefore more heat is retained by the pads.

    Quote Originally Posted by UP Dude
    To their credit, you could probably go 5 years or more on one disc.
    How do you arrive at this figure? You need to rid yourself of the tendency to describe bicycle component lives in terms of vague units of time since these don't make sense. Use usage time instead, eg "you could probably go XX hours of usage on one disc".

    Quote Originally Posted by UP Dude
    Another metal I hadn't thought about until today was magnesium. It's a lot like aluminum as far as weight and the ability to move heat.
    What does "ability to move heat" mean?

    Quote Originally Posted by UP Dude
    The major difference is its ability to hold heat, more than ten times what aluminum can hold. I don't know exactly what heat capacity is (can anyone tell me?) but I'm guessing the higher the value, the better a metal performs at elevated temps.
    Heat capacity is not "ability to hold heat". Heat capacity is the amount of heat required to raise a substance's temperature by 1 degree. It's not a very useful parameter since it's size dependent; the larger the volume the greater the heat capacity, regardless of material. A better indicator is specific heat capacity, which is defined in terms of unit mass of substance.

    Mg alloys have an order of magnitude lower thermal conductivity than Al.

    Quote Originally Posted by UP Dude
    Carbon fiber brakes (rotors and pads) have been used on formula one cars for a few decades now. I don't know exactly what the performance numbers are on them, but if formula one is using them, chances are its the best.
    You need to qualify that by adding "best for its purpose", which doesn't involve durability.

    Quote Originally Posted by UP Dude
    Metal matrix composites are really cool. They can do amazing things to the mechanical properties of the standard metal,
    What problems do these offer solutions for?

    Quote Originally Posted by UP Dude
    Ceramics have been gaining steam lately, having ceramic coatings on rims and the introduction of ceramic rotors (made of a silicon carbide matrix with chopped carbon fibers) on high-end cars. What makes them so good? They're light, really light. Less than half the weight of iron automotive rotors.
    What's good for cars don't necessarily mean the same for bicycles. Bicycle brakes do nowhere near the same amount of work as automotive brakes.

    Quote Originally Posted by UP Dude
    They have a very high thremal conductivity coefficient, almost the same as aluminum,
    Incorrect. Zirconia, one of the most common ceramic substances, has two orders of magnitude lower TC than Aluminum.

    Quote Originally Posted by UP Dude
    And when they heat up, they have viturally no performance fade.
    It's not the ceramic rotor that has fade problems, it's the pads. Ceramic, being a very good insulator, prevents heat from being conducted away from the pads, which means very poor pad performance during heavy use.

    Quote Originally Posted by UP Dude
    There are two drawbacks; getting rid of all the heat they absorb and brittleness.
    Ceramics, or any other good insulators, DO NOT absorb heat as well as non-insulators. Heat is PREVENTED from being carried away by ceramic materials from pads.

    Quote Originally Posted by UP Dude
    Porsche collects air from the front and moves it to the rotors to cool them off, as well as having wheels that are designed like fan blades to pull air inside. Since bike rotors are exposed, cooling would be less of an issue.
    In ceramic rotor systems, it's the pads that are being cooled, NOT the rotors.

    Quote Originally Posted by UP Dude
    But if I were to gamble, I'd say ceramic rotors are the next big thing in mtn bike brakes.
    You might win, but not for the reason you're thinking of. What's going to give you better odds is the marketing hype that will be accompanied by these "exotic" rotors, and the well tested gullibility of people to buy into things because they're "high-tech" and made of "aerospace materials" which will have better "efficiency" etc etc.
    Last edited by Juramentado; 03-14-2004 at 01:38 PM. Reason: Brevity

  15. #15
    The Dude Abides
    Reputation: UP Dude's Avatar
    Join Date
    Feb 2004
    Posts
    212

    I've hired a lawyer to do my talking :-)

    I didn't realized I would be under such scrutiny for my post. I'll appologize to Juramentado for not writing with exact technical definitions. But I write loosely to make it more interesting and easier to read for riders with less technical backrounds. I mean who cares if I say formula one brakes are the best, not "best for its purpose." I said in the very next sentence they wear out quick. It gets the point across. Lighten up a bit. I though several of your quote replies were unnecessary and sounded cocky. You may not have meant them that way, but thats how they read to me. If you have a legitimit correction, it'd be cool if you were a bit more compassionate about it.

    Thanks for relaying what heat capacity was. Do you know what the practical effects of it are? Or I guess the practical effects of specific heat capacity?

    I'm no expert on ceramic brakes, pretty much just what I wrote the first time. If you know more, I'd love to learn. The ceramics as insulators thing was a good call. I'm punching myself in the face now for saying that they aren't, but I must have seen a number somewhere that would lead me to believe it.

    I'm sure it would be really fun to get into geeky engineering chat with you since most of my knowledge comes from reading, not practice (fair since I'm only a student). I only have time to check posts like twice a week though. I'll definately be checking in those days to see whats up. I love brakes, so I'm always interested in new stuff.

    And for everyone else. I just learned today that an aerospace company (I've forgotten the name now) is making aluminum metal matrix rotors with silicon carbide fibers. I've been proven wrong on the whole thermal properties it seems. But supposedly they are like half the weight of a standard rotor. Here comes the harsh part......$110 per rotor!!! Not quite worth it if you ask me.

    Happy Trails

  16. #16
    Baliw
    Reputation:
    Join Date
    Jan 2004
    Posts
    203
    Quote Originally Posted by UP Dude
    I didn't realized I would be under such scrutiny for my post.
    I've done so because I think your effort to inject technical credibility into the subject is to be applauded. It's not meant to be a put down; you had many things correct in your post. I'm sure you'll find when you start practicing in your qualification that your reports and analyses will be scrutinised much more rigorously in terms of technical veracity, and any hint of emotive opinion will always be the Achilles heel of your work.

    Quote Originally Posted by UP Dude
    But I write loosely to make it more interesting and easier to read for riders with less technical backrounds.
    I'm all for plain English for explanations of technical concepts. The danger exists though that things sometimes get oversimplified and as a result, become misleading.

    Quote Originally Posted by UP Dude
    I mean who cares if I say formula one brakes are the best, not "best for its purpose." I said in the very next sentence they wear out quick. It gets the point across.
    The point that you conveyed is that technology transfer between two totally different pursuits is always applicable and "best". Sometimes this is true, but many times it is not. My point is that the technology in F1 brakes is not likely to be of relevant and significant benefit to bicycle brakes, because the duty cycles are quite different between the two applications. F1 components are meant for much higher performance than any bicycle will ever equire, and are not made to be durable in acceptable consumer definition; these need only last one race and are made as such. Add to that the cost of transferring such technology to bicycles and you have a marketing jock's wet dream.

    Quote Originally Posted by UP Dude
    Lighten up a bit. I though several of your quote replies were unnecessary and sounded cocky. You may not have meant them that way, but thats how they read to me. If you have a legitimit correction, it'd be cool if you were a bit more compassionate about it.
    On the contrary. I'm unaware of any ad hominem attacks in my reply to your post. In fact, I think it's refreshing to see posts that have some technical basis from people with technical backgrounds. It should be encouraged since there aren't nearly enough of these in these fora. Scrutiny and challenges to technical opinions come with the territory though, and I'm not exempt from that either.

    I don't like to use emoticons though, so you might read the tone of these posts incorrectly.

    Quote Originally Posted by UP Dude
    Thanks for relaying what heat capacity was. Do you know what the practical effects of it are? Or I guess the practical effects of specific heat capacity?
    SHC gives an indication of the insulating effects of a material (or the energy required to heat it). Hence it also gives an indication of how much a material allows heat to be conducted from one spot to another.

  17. #17
    The Dude Abides
    Reputation: UP Dude's Avatar
    Join Date
    Feb 2004
    Posts
    212
    Thanks man. Perhaps we'll cross technical paths again sometime.

Similar Threads

  1. marco very much likes xtr discs!
    By marco in forum Weight Weenies
    Replies: 20
    Last Post: 02-24-2004, 04:55 PM
  2. weight/peformance of v-brakes vs. discs
    By jcospo in forum Weight Weenies
    Replies: 91
    Last Post: 02-21-2004, 11:04 PM
  3. Just got some new mech discs and dang they're light...
    By DeeEight in forum Weight Weenies
    Replies: 11
    Last Post: 01-31-2004, 01:40 PM
  4. Juicy Rotors with Cable Discs?
    By ScaryJerry in forum Brake Time
    Replies: 10
    Last Post: 01-29-2004, 06:22 AM
  5. Replies: 1
    Last Post: 01-13-2004, 10:47 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •