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  1. #1
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    brake rotor material: Why stainless steel?

    Why is it that most of the brake rotors I see that advertise the type of steel they use are stainless steel?

    Stainless steel has the worst thermal conductivity of almost any metal except titanium alloy.

    Aluminum is very good for thermal conductivity, but too soft to last, which is why shimano's sandwiched design makes sense.

    But, why not just use regular old carbon steel, which has 3 times the thermal conductivity of SS at a lower cost?

    Is it because most bikes sit around in bad weather, and would rust too much between uses?

    Since I keep my bike inside, and use it daily, are there some decent light weight carbon steel rotors available? It seems the higher thermal conductivity would allow using less material(more holes, or smaller diameter) without worrying about overheating.

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    brake rotor material: Why stainless steel?

    Rust.

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    unless you let your bike sit out in the rain, and rarely ride it, why worry about rust?
    It is constantly being polished by the pads.

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    The brake track itself is kept clean & rust free by the pads, the rest of the rotor, well, that's a bit of a problem. In a car or other motor vehicle it's not a big deal since the disc itself is over an inch thick, it's going to take quite a few years for the rotor to rust to the point where its strength is compromised. On a bike where the rotor is only 2mm thick at most, it doesn't take much rust before the rotor gets weakened to the point where it's unsafe.

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    Rust can really destroy it but if you take good care of your bike, you don't really need to use stainless steel or worry about rust..
    Last edited by Max24; 03-02-2015 at 05:47 PM.

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    Manufacturers know that many owners are going to leave wet mud splattered on the rotors, why build from a material that's guaranteed to result in lots of consumer complaints and returns?

    How many people dry their bikes off with a cloth or hair drier? Water left on a surface for even half a day as it dries off can result in rust (check out what happens to a chain that is stored indoors but isn't lubed well).

    If you really want carbon steel rotors, take a set of generic rotors to a good metal store and have them cut something out of a sheet.

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    Quote Originally Posted by Max24 View Post
    Rust can really destroy it but if you take good care of your bike, you don't really need to use stainless steel or worry about rust.
    I'm a mountain biker, not an OCD mechanic. Unlike frames, gears, chains, and various nuts & bolts, I can't oil or rust proof a brake rotor in any way. Unless I dry the rotor immediately after every ride and store the bike in a nice dry place it's going to rust, and I don't have that kind of time & energy. Well, I do, but it would piss me off to the point where I give up mountain biking or go back to V-brakes.
    Last edited by aerius; 02-24-2013 at 07:25 AM. Reason: typos

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    I'll put other peoples words into different words, and hope it also makes sense to the OP.
    Because the material choice was made based on a marketing decision, and not an engineering decision.

  9. #9
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    Because stainless works just fine, and doesnt rust. The decision was definitely made from an engineering perspective, carbon steel would be a terrible choice.

    A carbon steel rotor would rust. I dont know about you, but I dont want to be wire brushing my rotors after every ride to keep rust off. Regular carbon steel rotors will rust from moisture in the air. The rusting is removing material from an already very thin rotor. You'd be replacing rotors often, and we'd see people breaking rotors off the hub frequently.

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    Quote Originally Posted by One Pivot View Post
    Because stainless works just fine, and doesnt rust. The decision was definitely made from an engineering perspective, carbon steel would be a terrible choice.

    A carbon steel rotor would rust. I dont know about you, but I dont want to be wire brushing my rotors after every ride to keep rust off. Regular carbon steel rotors will rust from moisture in the air. The rusting is removing material from an already very thin rotor. You'd be replacing rotors often, and we'd see people breaking rotors off the hub frequently.
    While it is true that stainless works just fine ... Without modeling one up and performing thermal emmissivity vs thickness , the choice to go with stainless is a factor of marketability (keep it pretty), and not one of performance.



    Gray cast iron that is precision flat ground has dominated the disc brake industry for years, on every vehicle except a bicycle.
    Second place goes to ductile Iron ... Blame the cosmetic conscious, and weight conscious for the decision ... Also those who don't like shattered rotors (gray cast), after a crash

    But don't take my word for it...................
    More on iron brake rotors

    --------------------------------------------------------------------------------

    Great overview Shazaam.

    Would like to take this opportunity to clarify a couple of points.

    Traditional iron brake rotors such as widely employed in the automotive industry and to a much lesser extent, in the motorcycle aftermarket are Gray iron. That material is features a distinctive coarse flake molecular structure and typically suffers from issues of porosity that can lead to failures associated with thermal stress induced fracturing. To address these inherent material weaknesses, improve their failure resistance and increase thermal capacity, they are typically big and heavy. This whole reliability issue is made worse by the nearly universally employed individual mold casting technique...cheap and efficient to be sure, but also guarantee's even more problems associated with uncontrolled porosity.
    The widely reported untimely demise of Jimmie Adamo is much as described, but that too was Gray iron and simply not up to the task.

    The Ductile iron family is a different animal, developed in the mid 1940's specifically to deal with the inherent brittleness of Gray iron. Ductile iron features a unique spheroid - nodular molecular structure that introduced "ductility" into the matrix. This brought many benefits to the manufacturing industry with a much more reliable base material including substantially higher tensile strength, inherent resistance to thermal stress induced fracturing, improved thermal conductivity and more. Within that broad family of Nodular (ductile) iron, there are many variations, just like there are in the general steel family. Without getting too boring with unnecessary minutia, suffice to say the specific grade of iron used in the manufacture of BrakeTech AXIS/Iron rotors is an optimal alloy with a closely monitored and proprietary heat-treating process employed for both stress relieving and material hardness. We also utilize a specialized in-house Cryogenic treatment of LN in a computer control vapor system at -300F. Contrary to what is out in the ether sphere of the web, the cryo processing we employ converts austenitic carbon/graphite atoms to martensitic for much improved wear (abrasion) resistance. Our testing shows the cryo processing has little real-world affect on relieving residual material stresses. That aspect of manufacture is addressed in our proprietary and more traditional heat-treating.

    Also, unlike the individually molded Gray iron mentioned at the outset, the BrakeTech ductile iron is manufactured from true billet, no individual molding here. We quite literally saw blanks from continuous cast bar containing virtually zero porosity. Every step of manufacturing is closely monitored to a remarkably high level and ISO 9001 standards (each finished iron blade is micro laser etched with all relevant batch and date info, look closely at the patented and trademarked Direct-Link "tooth" and you'll find that).

    Quick note on perceived weight of iron versus stainless; contrary to popular belief, the misconception that iron is heavier than stainless steel is simply not true. The density of iron is slightly lower than that of common stainless, so for a given volume of material, iron will be somewhat lighter. Perception always plays a role; kinda like asking an unsuspecting friend, “which is heavier, a pound of feathers or a pound of lead?”

    Lastly, the real reason the OE's don't use iron is primarily one of aesthetics; the potential of rusting rotors is very simply not palatable. A secondary reason is the greater expense of manufacturing from a proper grade of higher spec ductile iron, costs are always an issue. And lastly, advances in friction material technology for use on stainless steel have come a long way, their performance as well all know is nothing short of brilliant...it's just a bit better still on iron!

    My apologies for the lengthy response...it's a convoluted subject so "sound bite" like replies doesn’t cut it.

    Best wishes and safe riding to all.

    Jeff Gehrs
    BrakeTech USA
    Iron Brake Rotors - Ducati.ms - The Ultimate Ducati Forum
    If it was a pure performance decision, the decision would go to iron.

  11. #11
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    Safety takes strong priority over pure performance. Rust is real. Its also quite easy to break a 2mm thick piece of ductile iron.

    Cars and motorcycles dont use 2mm thick rotors, its not the same conversation with them.

    We have lots of super high performance near-disposable bike parts, but brake components shouldnt be one of them.

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    Corrosion is a non issue, it's all marketing... you don't need an engineer to figure out that iron can be galvanized or coated with other stuff such as Titanium Nitride.

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    Quote Originally Posted by One Pivot View Post
    Safety takes strong priority over pure performance. Rust is real. Its also quite easy to break a 2mm thick piece of ductile iron.

    Cars and motorcycles dont use 2mm thick rotors, its not the same conversation with them.

    We have lots of super high performance near-disposable bike parts, but brake components shouldnt be one of them.
    Safety to a consumer acceptable degree, but more so to a manufacturer lawyer acceptable degree ... If the average consumer didn't have a seemingly unlimited supply of disposable income, the near-disposable bike parts would not exist.

  14. #14
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    Quote Originally Posted by syl3 View Post
    Corrosion is a non issue, it's all marketing... you don't need an engineer to figure out that iron can be galvanized or coated with other stuff such as Titanium Nitride.
    LOL... How far into the metal do you think a coating will go? Nevermind that some of these coatings will act as lubricants in certain instances.

    I'm pretty surprised that nobody has flamed the OP or any of their others here, Stainless Steel serves the purpose very well. Its low maintenance, it looks nice and its relatively cheap, to mfg.

    Whomever is heating their brakes beyond the limits of the rotor material, the fluid or the friction material is breaking new ground in cycling...

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    any number of coatings would prevent rust in all areas except the frictionsurface, but would wear away pretty quickly there, unless fairly thick and hard. I aagree that stainless seems to work ok for most uses, but I would think downhill racing would have fading performance with stainless steel, and rapid pad wear, since the pads are mostly cooled by the rotor. I am sure that normal wear from use will affect the structural integrity of the rotor long before rust can if used even once in a while. I think that as thin as bicycle rotors are, ductile iron would work, but still have some issues of breaking from impacts. I was suggesting regular high carbon cold rolled steel, which doesn't have as good of thermal properties as grey, or ductile Iron, but much better than stainless, while being stronger than the Iron rotors. I do see how it would be unappealing to see an orangish patina on the friction surface when you pick up your bike that's been sitting out in the rain, but I don't see any practical reason to use stainless. In fact a light scale of rust between uses would probably help keep things roughed up a little, preventing that aweful howling noise when it's humid.

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    double post

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    You're trying to solve a problem which doesn't exist for the vast majority of mountain bikers. The percentage of riders who have issues with brake fade is somewhere in the low single digits, and for those folks we have vented rotors from Hope and Ice Tech rotors from Shimano. Everyone else gets along just fine with stainless steel rotors (aside from the Avid turkey gobble) which are low to zero maintenance and provide all the performance they need.

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    Quote Originally Posted by aerius View Post
    You're trying to solve a problem which doesn't exist for the vast majority of mountain bikers. The percentage of riders who have issues with brake fade is somewhere in the low single digits, and for those folks we have vented rotors from Hope and Ice Tech rotors from Shimano. Everyone else gets along just fine with stainless steel rotors (aside from the Avid turkey gobble) which are low to zero maintenance and provide all the performance they need.
    Naa,
    I got the question, and it seems valid.
    Quote Originally Posted by autodoctor911 View Post
    But, why not just use regular old carbon steel, which has 3 times the thermal conductivity of SS at a lower cost?

    Is it because most bikes sit around in bad weather, and would rust too much between uses?
    Why Stainless when a non-stainless would work just as well, or better ... And the answer really is,
    Cosmetic appeal ... Most people like shiny, and hate rust.
    .
    .
    Hey !
    Cool $10,000 bike, but the brakes are all rusty ... You should upgrade
    .
    .

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    Quote Originally Posted by bikeabuser View Post
    Why Stainless when a non-stainless would work just as well, or better ... And the answer really is,
    Cosmetic appeal ... Most people like shiny, and hate rust.
    As a former bike mechanic, I know how well the the average person takes care of his/her bike. Give'em a non-stainless rotor and I guarantee that rust-through failures will become a common occurrence.

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    Quote Originally Posted by aerius View Post
    As a former bike mechanic, I know how well the the average person takes care of his/her bike. Give'em a non-stainless rotor and I guarantee that rust-through failures will become a common occurrence.
    I'm not prejudiced against stupid people, but take away the labels and let the solution take care of the problem

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    Yep, really rust and corrosion is the number one reason.

  22. #22
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    brake rotor material: Why stainless steel?

    Quote Originally Posted by syl3 View Post
    Corrosion is a non issue, it's all marketing... you don't need an engineer to figure out that iron can be galvanized or coated with other stuff such as Titanium Nitride.
    You don't have to be an engineer .... Too figure out that this is a pretty stupid* comment. Coating? A brake rotor disc? C'mon... Think about that for a moment. Its difficult to hold close tolerances when you hot dip galvanize steel or iron, and electroplated galvanize is expensive and leaves a very thin coat. Both methods are a few mils thick and would wear off rapidly.

    * Note- Stupid, but only in my opinion, but l do have a degree in metallurgy and materials engineering. CRSS is a fantastic material for a mountain bike brake disc rotor. It's the material I would select if I was spec'ing a rotor. (Titanium Nitride? Hmmmmmm wonder what that would cost?). Stop reading this thread and go do something productive. Like riding. Just saying.
    Last edited by Scott In MD; 02-24-2013 at 04:55 PM.

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    Just stick it in granny and start grinding.

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    I know about the kettle sicc rotors, and I will be getting some of those, which are far superior to any metal rotor. I was just posing the question because I noticed during my research of the thermal properties of various materials that stainless steel seemed to be a poor choice. Iron or high carbon steel would give better friction and thermal properties than stainless steel, and reduce the weight by about 10%, but the SICC rotors will give even better friction and reduce weight by 50%. Of course, they will cost twice as much, but the reduced wear will make up for that somewhat.

    corrosion, in the normal sense will also not be an issue with the SICC rotors, although they will degrade with time, and sunlight.

    I also learned recently that most stainless steel brake rotors are made of high carbon stainless of the 420-430 grade, which is much better at thermal conductivity and friction than the shinier 3xx series stainless steels. Thus the desparity in performance compared to iron is not as much as I had thought, and may be comparable to regular cold rolled high carbon steel.
    Last edited by autodoctor911; 02-25-2013 at 04:08 AM.

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    I like the SICC rotors, but they are probably not in my future.
    I have a feeling we will see some breakage on the trails with these.

    I see them as a great race application, just not a good daily bike application.
    Just stick it in granny and start grinding.

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    I am thinking they will be fairly tough. I am thinking an impact that would break them would also bend a stainless steel rotor enough to make it unusable. Of course, it would be a lot cheaper to replace the steel one. If I break one I may revert back to the standard ones.

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    Quote Originally Posted by Scott In MD View Post
    You don't have to be an engineer .... Too figure out that this is a pretty stupid* comment. Coating? A brake rotor disc? C'mon... Think about that for a moment. Its difficult to hold close tolerances when you hot dip galvanize steel or iron, and electroplated galvanize is expensive and leaves a very thin coat. Both methods are a few mils thick and would wear off rapidly.

    * Note- Stupid, but only in my opinion, but l do have a degree in metallurgy and materials engineering. CRSS is a fantastic material for a mountain bike brake disc rotor. It's the material I would select if I was spec'ing a rotor. (Titanium Nitride? Hmmmmmm wonder what that would cost?).
    Name:  titanium nitride rotor.jpg
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    Alligator Wind-Cutter Titanium Nitrite Coated Rotor at Price Point

  28. #28
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    Quote Originally Posted by Scott In MD View Post
    You don't have to be an engineer .... Too figure out that this is a pretty stupid* comment. Coating? A brake rotor disc? C'mon... Think about that for a moment. Its difficult to hold close tolerances when you hot dip galvanize steel or iron, and electroplated galvanize is expensive and leaves a very thin coat. Both methods are a few mils thick and would wear off rapidly.
    There is absolutely nothing touching the rotor outside of the braking area, so why exactly would the coating wear off? And on the braking surface there would be no tolerance problem because you don't need any coating, braking friction would keep the surface rust free, in fact it would be quite shiny.

    * Note- Stupid, but only in my opinion, but l do have a degree in metallurgy and materials engineering. CRSS is a fantastic material for a mountain bike brake disc rotor. It's the material I would select if I was spec'ing a rotor. (Titanium Nitride? Hmmmmmm wonder what that would cost?). Stop reading this thread and go do something productive. Like riding. Just saying.
    You may be an armchair metallurgist but i suggest you take your head out of your... ahem... antiquated textbooks and take a look at alligator and ashima Titanium Nitride coated rotos, they already exist and they cost very little extra. The same thing is used for gold colored chains such as KMC X9 SL and Token's tiramic bearings with ceramic balls and coated steel races. You would think that they wear off fast but in fact the coating is pretty hard, sometimes even harder than the steel itself. Some full ceramic bearings are also made of Nitride, but most usually Silicon Nitrade

  29. #29
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    Ideas are OK; then they get vetted. But we shouldn't stop thinking. Lots of "really bad ideas" 20 years ago are standard now. You've probably already thought of 1; and now probably another.

    I used to frequent a Subaru forum (NASIOC) and on a fairly regular basis a thread would pop up saying "I just washed my car and my brakes are rusty. How do I clean it off? Do I need new rotors? Subaru puts on s****y rotors." It was described by people with more knowledge than me as 'flash rusting.'

    While obviously not an issue with with car rotors (as stated earlier in this thread), a 2 mm thick rotors is another issue (ASEITT). Which leads me to wonder if carbon steel would actually be superior to stainless from a pure performance point of view (I'm not a metallurgist and did not stay at a Holiday Inn Express either). Many high temperature coatings exist which could cover the areas not swept by the pads.

    If marketed right, with the high temp anti-rust coat, if there was the SLIGHTEST performance advantage, you all know there would be people proud of the fact that their rotors rust. There'd be people who think they needed it too. Probably the same people.

    Tough for me to really care as I don't/can't outride my Ice-Tech's, but it's an interesting topic.

    Steve

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    Quote Originally Posted by syl3 View Post
    Corrosion is a non issue, it's all marketing... you don't need an engineer to figure out that iron can be galvanized or coated with other stuff such as Titanium Nitride.
    This is not posable, galvanisation or any coating would be worn off by the brake pads.

    Stainless is just about the best thing you can use, it doesnt rust nor contaminate brake pads.

    For those of u that dont understand rust, it happens in a matter of hours not days.
    And when it happens it will contaminate the pads.

    Stainless is pretty strong, doesnt crack much, is cheap, and doesnt rust, its the perfect thing to use for rotors
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    Quote Originally Posted by Tone's View Post
    This is not posable, galvanisation or any coating would be worn off by the brake pads.

    Stainless is just about the best thing you can use, it doesnt rust nor contaminate brake pads.

    For those of u that dont understand rust, it happens in a matter of hours not days.
    And when it happens it will contaminate the pads.
    Umm... nope

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    Quote Originally Posted by syl3 View Post
    There is absolutely nothing touching the rotor outside of the braking area, so why exactly would the coating wear off? And on the braking surface there would be no tolerance problem because you don't need any coating, braking friction would keep the surface rust free, in fact it would be quite shiny.



    You may be an armchair metallurgist but i suggest you take your head out of your... ahem... antiquated textbooks and take a look at alligator and ashima Titanium Nitride coated rotos, they already exist and they cost very little extra. The same thing is used for gold colored chains such as KMC X9 SL and Token's tiramic bearings with ceramic balls and coated steel races. You would think that they wear off fast but in fact the coating is pretty hard, sometimes even harder than the steel itself. Some full ceramic bearings are also made of Nitride, but most usually Silicon Nitrade
    Full ceramic bearings are OK for a race bike, and perhaps even a daily use road bike, but an MTB in daily use ... Not a good choice, IMO.

    The rest of it ... As soon as marketing convinces enough people, we'll probably see rotors available in a rainbow of colors.

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    Hi,

    I am an Engineer that works with small electric vehicles (not bikes) but have dealt with brake design before. I realized this post is pretty old but I thought others that might happen upon could benefit from my response.

    You are right to consider the thermal aspects of the brakes as important and sometimes the thermal conductivity is important, however in the case of small rotors (think motorcycle, ATV, UTV, and bikes) the dominating mode of heat transfer is not internal convection. Small rotors will be about the same temperature throughout the disc.

    If you really want to check for your self you can look up how to calculate the biot number. If you do you will find it to be very small and this means that the material conductivity or internal conduction is not important to the problem. Rather the convection from the disc to the air is the dominating factor and is not dependent on the thermal conductivity of the rotor material.

    Also for brakes the Pads are an important consideration. Stainless steels are hard and allow for use of harder sintered pads that contain metals. This lowers the pads thermal resistance and allows more heat to be dissipated to the pads. Also sintered pads last longer and are less prone to fade than organic pads. They are also better in wet and muddy conditions making them ideal for mountain bikes.

    I personally think it is generally not a good idea to add coatings to rotors. It is effectively like putting gum in between the pad and disc until it is completely removed. There maybe applications where coatings make sense but generally they are a bad idea. I have dealt with brake companies that coat rotors that probably shouldn't have.

    Stainless really is a great material for this application not even considering the corrosion resistance it provides. It is not a gimmick.

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    Great first post.

    FYI for clarity you should edit your text "the dominating mode of heat transfer is not internal convection." by changing the word "convection" to "conduction".

    I also suggest using the Nusselt number (Nu) instead of the Biot number (Bi) for the analysis. Nu links h to the fluid properties via the Reynolds number (fluid flow characteristics) and the Prandtl number (heat transport characteristics within the fluid). Bi is for analyzing internal gradients within a solid.

    I agree with your description of the benefits of stainless steel.

    Kind regards.
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    Why do manufacturers insist on using a material that has worked perfectly well for decades? It's a conundrum right enough...

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    Quote Originally Posted by Scott In MD View Post
    You don't have to be an engineer .... Too figure out that this is a pretty stupid* comment. Coating? A brake rotor disc? C'mon... Think about that for a moment. Its difficult to hold close tolerances when you hot dip galvanize steel or iron, and electroplated galvanize is expensive and leaves a very thin coat. Both methods are a few mils thick and would wear off rapidly.

    * Note- Stupid, but only in my opinion, but l do have a degree in metallurgy and materials engineering. CRSS is a fantastic material for a mountain bike brake disc rotor. It's the material I would select if I was spec'ing a rotor. (Titanium Nitride? Hmmmmmm wonder what that would cost?). Stop reading this thread and go do something productive. Like riding. Just saying.

    I agree... ISR Brakes use CRSS as it disiaptes heat faster than cast iron and does not crack or shatter. Yamaha were using cast iron discs back in the 1980's before Carbon was used (Yamaha were the first 500cc GP team to use carbon) the discs used to crack every race. But they put up with it as Iron gave the best properties for friction and the strongest brakes. ISR spoke to Yamaha about CRSS discs and Yamaha just dismissed it say all discs crack and it was just one of those things and were happy with the supplier (sponsorship means they were getting them for free... ISR would be selling them to Yamaha so why pay when Brembo were giving them free discs??) So ISR took a rotor and folded it in half and stuck a business card in between the fold with a simple "Our discs do not crack!" written on it.... After that ISR supplied discs until the advent of Carbon brakes.

    Titanium Nitride is a tough coating but the down side is that is it also a low friction coating. So the brake performance will suffer.

    Now wave or saw shaped discs with a lot of cutaway areas are one of my pet peeves. Used to see them used in motorcycles too... But this is another area that can have a big effect on brake performance. The waves and jagged shapes can give you great brake power when new as they are lazer cut and very sharp edges which bite into the pads. The softer the pad the better their performance initially. As the edges dull the performance goes down. Brakes work by clamping on the disc not clamping on fresh air. The more air there is the more it relies on the sharp cutting effect of the edges on the pads and you have increased pad wear. A good fully round disc of a CRSS will work better long term.

    (CRSS is a Cold Rolled Stainless Steel, Not all stainless steel discs are cold rolled and many are just lazer cut from plate then ground and do not have the granular structure of CRSS so do not have the same frictional properties)

  37. #37
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    Re: brake rotor material: Why stainless steel?

    Quote Originally Posted by ca_rider View Post
    Great first post.

    FYI for clarity you should edit your text "the dominating mode of heat transfer is not internal convection." by changing the word "convection" to "conduction".

    I also suggest using the Nusselt number (Nu) instead of the Biot number (Bi) for the analysis. Nu links h to the fluid properties via the Reynolds number (fluid flow characteristics) and the Prandtl number (heat transport characteristics within the fluid). Bi is for analyzing internal gradients within a solid.

    I agree with your description of the benefits of stainless steel.

    Kind regards.
    Actually no. The rotor heats locally where it contacts the pad and the rotation carries the heat out from the contact. That's convection. He's saying that this isn't an important heat loss mechanism as the disc temperature is fairly homogeneous. Hence also the Biot number.

  38. #38
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    Quote Originally Posted by henkm View Post
    Actually no. The rotor heats locally where it contacts the pad and the rotation carries the heat out from the contact. That's convection. He's saying that this isn't an important heat loss mechanism as the disc temperature is fairly homogeneous. Hence also the Biot number.
    Sorry, in my fields (ChE and ME) we use differing terminology. In brief, given conductivity is not important as stated, then diffusion is negligible and the transport within the rotor is advective, not convective. I'll refrain from further digression.
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  39. #39
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    Quote Originally Posted by ca_rider View Post

    FYI for clarity you should edit your text "the dominating mode of heat transfer is not internal convection." by changing the word "convection" to "conduction".

    I also suggest using the Nusselt number (Nu) instead of the Biot number (Bi) for the analysis. Nu links h to the fluid properties via the Reynolds number (fluid flow characteristics) and the Prandtl number (heat transport characteristics within the fluid). Bi is for analyzing internal gradients within a solid.

    I agree with your description of the benefits of stainless steel.

    Kind regards.

    Thanks, I did mean internal conduction. I focused on the biot number for insight to the problem and the nusselt number (a function in this case) would be required for a true analysis.

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