You should be able to figure out just by using your brain. If you have a rotor in open air, it cools one way. If you surround it with something that is highly insulating that is also almost touching it... then duh of course the air will not cool it as evenly.
I really have to question if one square inch -- or less -- of ceramic impregnated resin is "highly insulating" given they seem to get just as hot. To the point I was able to smoke them on a hill. Admittedly steel's s*it heat absorption and dissipation is why it's so prone to heat expansion/contraction issues, again the surface area to mass ratio should reduce that problem.
This is standard training for high performance (i.e. race track) driving and the problem is worse, not better, on a bicycle because the rotors are soooo thin the heat sink that is a brake rotor has far less material to work with.
In a material that has absolute garbage heat absorbing, storage, and dissipation. Irregardless of the material though, the thinner the rotor the more surface area per mass, thus the faster they can cool. Bigger thicker rotors cool
slower because of their reduced surface to mass ratio. Just as thicker rotors should be more prone to warping as they cool akin to a bad temper, such as the difference between a nail and a shoe. I was a farrier's apprentice for a bit, so I know a wee bit about metalworking, forging, etc.
Again why I put thermal compound on my front rotor where the aluminum hub meets the steel disc. That contact point should be sucking the heat out of the rotor.
oh hell yes. I've got a front rotor right now I can't fix because of it.
Have you tried torching it to relax the metal?
Thats because you are all worked up and not reading carefully. I said such a technique was used when bedding the rotors. Anyone with any brains is bedding their brakes on a sleepy neighborhood road thats not an alpine descent.
Some of my sleepy neighborhoods ARE "apine descents". Though what you were quoting wasn't referring to "bedding them in" I was referring to during a normal everyday ride.
If you have to stop on a steep downgrade (like at a stoplight), you reach your 'stop' point a few cars back.
You utterly, totally, and completely misunderstood what I was saying. Which seems to go hand in hand with your not seeming to understand much of anything I'm trying to say.
I was not referring to a normal stop, I'm referring to where you're halfway down a hill and HAVE to stop because your brakes are losing grip and/or blowing smoke. How the bloody hell are you supposed to continue going down "gently" to let things cool off when you're halfway down a hill and they're overheating? That's not just directed at you either. This "oh just slow down to let them cool" s*it
doesn't mean anything in places where you're choices are stop completely or go 40+.
Aka almost every "normal sleepy neighborhood" to the east of where I live.
I was
NOT referring to a normal stop like an intersection.
Brake rotors are heat sinks. More material in the rotors means more heat can be sunk into them.
Which with steel is a dumb idea, as it will retain the heat too long... with the larger thermal mass again having a lower surface to mass ration, basically CREATING warping when/if you bring them up to temperature. Same fallacy as liquid cooling on PC where once you hit the thermal limit of your coolant, you're prolonging heat when the load stops. Depending on the performance regime it can do more harm than good in the long term.
Reality not stopping hundreds of so-called "experts" from extolling the virtues whilst sweeping the problems under the rug. Card stacking at its finest and a way to sucker people into wasting money on a bad, high maintenance, situation dependent solution.
I thought that's why a lot of rotors I was looking at had aluminum hubs, lots of holes in them, etc. Increase the surface area and use a secondary metal with better thermal properties.
I'm a little surprised nobody has made a rotor with heat pipes on it.
Thats because you are all worked up and not reading carefully. I said such a technique was used when bedding the rotors.
The statement you quoted wasn't directed at you specifically, and again you didn't understand what was being said. Read the blood thread, nearly everyone is saying to slowly swap between front and rear when going downhill, to alternate betwixt the two.
I don't understand how you do that without going over the bars when applying enough pressure for the fronts to do... anything of value on a real hill.
My saying that had / has not one single Joe-blasted thing to do with bedding in brakes.
This is why sports cars and race cars have huge brake rotors.
And why they are often two thin disks with large amounts of porting between them to force more air through and REDUCE the mass / increasing the surface area for better cooling.
Because the material used is a garbage heat sink.
Its also why things like alloy hats on 2-piece rotors decrease the severe-duty effectiveness of a brake rotor because they reduce the mass that can absorb heat (their benefit is reducing rotating mass).
Utter poppycock depending on the material, given that aluminum by mass and surface area outperforms steel anywhere from 8 to 20 : 1 depending on the alloy. Simple thermodynamics.
There's a reason copper and aluminum are preferred for heat sinks in nearly every industry.
Again steel's crappy 16..40 wm/k to aluminum's 160..240 wm/k. Aluminum, copper, and silver are your friend if you want to get rid of heat and/or prevent something from overheating. As is surface area, not mass.
It's akin to radioactivity, where a large radioactive mass emits less radiation than a smaller one due to again "surface to mass". Aka "density". Thus why radioactive dust with a larger surface area to mass ratio makes places like the Pripyat exclusion zone more dangerous on windy days. Or why walking on the surface is far less dangerous than doing something dumbass like digging trenches there.
My heart bleeds for the Russian soldiers who weren't even told where they were and are now dying of radiation poisoning. Not bad enough the war crimes against an enemy without committing them against your own troops.
Bicycle rotors will rust. I keep some bikes at the coast and the progression is slow but its there.
ALL ferric metals rust, it depends on the environment. In fact stainless rusts faster in highly corrosive environments than even normal iron. Stainless just rusts slower in low corrosive conditions. Like a rope mill I worked at where the beeswax boilers for the lariat were these giant 80 year old iron tubs that needed to be replaced. The new ones were custom made out of stainless by so-called "experts" and they rusted clear through in six months. Under really nasty conditions iron > high carbon > stainless. Under mild conditions it's the other way around.
I think I mentioned it before in this thread, there's a reason seafaring ships use sacrificial anodes.