Difference between types of brake pads?

[Johan Bornman]

 

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Ceramic Brakes are made from ceramic fiber which is very good at dissipating heat.

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I find "dissipating" too vague to help me understand what's happening inside the pad or, what's claimed that is happening inside.

 

These ceramic fibres, are they good conductors of heat or good radiators of heat. In other words, by what mechanism does the dissipation work?

[Johan Bornman]

JB: interesting statement there suggesting heat is only generated in one or the other surface. That defies Newton 3 wrt the frictional forces at play. Also the pad is hardly that bad a conductor of heat, as the caliper gets hot enough to have an effect on the brake fluid behind the piston.. brake fade...only source of heat is the whole pad, not just the surface of it. The disc is just more effective at dissipating the heat generated by the friction under braking by windage over the structure of the disc itself, which you've alluded to.

Cassie, you may just be right in guessing that it's probably to better insulate the rest of the caliper from the ill effects of heating (whole pad as heat source). IIRC I think Shimano has gone so far on it's latest XT or XTR brakes to add heatsinks to the pad/caliper. lemme find it..

 

Capricorn, this was an interesting debate until you decided to put words in my mouth. I attempted to explain a general phenomena that covers a range of situations from rubber on aluminium (your road bike) through to hard pads on hard stainless steel discs.

 

The heat is mostly generated by whichever material experiences the most stretching and breaking of molecular bonds and this is whichever of the two surfaces wears first. That doesn't mean the other one experiences zero wear and hence heat generation.

 

Further, the heat is generated at the interface. That is the only source of heat. Not deep inside the material like you allude to. If there is any heat transfer to happen, it will mostly go to the surface that is the most eager to accept it - usually the rim (aluminium) or the disc - stainless steel.

 

Yes of course, if the pad is made of copper, heat will travel into the pad and ultimately into the piston and fluid etc etc. That's clear to most of us.

 

At the same time, if the pad is resin (and if resin is a poor conductor) then most of the heat goes to the disc. This doesn't mean that other parts dont heat up as well. Radiation also happens and the closest parts will absorb it. Yes, some heat will travel through the resin.

 

Now, onto the layered caked of a metal, ceramic metal disc pad. I'm sceptical. This would mean that the pad will display three different characteriscs as it goes through its wear life. I think it is stupid, but that's me. Why not just make the backing plate from something non-conductive and have a full-life pad instead? That would be less complex and cheaper. Maybe this was invented by marketing.

 

Finally, a heatsink on the backing plate will work if the pad is sintered metal with a lot of high-conductive metal inside. However, we don't see this on motorcycles or cars because most of the heat is dissipated via the disc and airflow around it. Their discs are also far, far more conductive than the stainless steel we see on bicycle discs.

[Capricorn]

... Heat is generated in the softer of the two surfaces. ....

 

That's a pretty definitive statement, which prompted my statement which clearly used the words "JB: interesting statement there suggesting heat is only ...". that definitive statement is in total contrast to the more factually accurate follow up in bold below (not the red bit).

 

Capricorn, this was an interesting debate until you decided to put words in my mouth. I attempted to explain a general phenomena that covers a range of situations from rubber on aluminium (your road bike) through to hard pads on hard stainless steel discs.

 

The heat is mostly generated by whichever material experiences .....

 

However, JB dont create issues where there are none by taking what was a rather soft statement meant to prompt clarification, as a personal crucifixion of your self. That's just petulant.

 

As for my statement which suggests heat is generated everywhere in the pad assembly, the intended context was that from the caliper's perspective, the whole pad is the source of heat. As a physical phenomenon, heat can only be generated at the point of friction. Agreed, of course.

Therefore, I also agree that my statement can be misleading.

[Johan Bornman]

Peace Brother, love and light and all that.

 

Due to time constraints, I sometimes apply the mantra of HH Munro (I have no clue who he is or was), that "A little inaccuracy sometimes saves tons of explanation. It occasionally gets me into trouble.

 

Back to the problem at hand.

 

Do you agree with me that the concept of sintered metal on a layer of ceramic, on a layer of whatever, just doesn't make sense?

 

 

I found a photo of the Ice Tech pads and appears that the friction material is on a baseplate of conductive metal. Behind that is another (presumably insolation) layer that makes contact with the pistons.

 

It appears that they want to drain heat from the pad and route it to the atmosphere, but prevent it from reaching the piston. Which makes sense on paper but I think this is a solution to a problem that doesn't exist. Imagine the cost of those pads.

 

Supposedly the problem is boiling fluid. They could fiddle with the boiling point of their oil - it is much, much lower than that of the Dot fluids (140 degrees vs 200 or so, IIRC). I just wonder how many people suffer from this problem and those who do - downhillers for instance, can address the problem in different ways.

 

This is one solution: a disc that's more conductive.

 

Quote from one of the spy sites: "The new Ice Tech brake rotors sandwich an aluminum layer between steel outer layers on the rotor, which helps them cool much, much faster than solid steel rotors."

 

The statement doesn't make sense, even though the concept does. The alu layer won't cool the disc faster but it will get the heat out of the disc into the spider and into the hub - provided the spider contacts the alu and not the stainless steel.

 

Again, imagine the cost of these discs. And soon every techno-yuppie with an imaginary disc overheat problem will be wanting them.

 

Fit cast iron discs, I say.

[dirtrider]

Looks like a lot of people don't know what the brakes ontheir bikes are for !! ?It is there for incase you need to stop . If you want to use your brakes to go slower , stop , get of and push .

[Capricorn]

I think the ceramic aspect is a bit of overkill. Granted, for DHers on super steep tracks, overheating could be a potential problem due to the extended braking.

 

But in general, they tend to stay off the brakes, so windage will long ago have solved the problem that sandwiches of metal was intended to prevent, in other words, a waste of time.

 

If I was forced to choose, I would rather just go with the heatsinks coming off the pad's backplate. I'm surprised they haven't gone the route of redesigning the caliper to faciliate more airflow thru the caliper and over the pads, or as with vehicles, redesign the brake disc to better self-cool as with vented and cross drilled discs found on performance vehicles (ignoring weight penalties of course).

 

But you've posed the operative question: why is all that fancy ceramic stuff necessary?

 

i think it's more marketeering than imagineering.

[Climate]

But Shimano have at least broached the topic of heat dissipation in rotors ... taken from a test of the new XTR M980 brakes: "Cooling fins are integrated into the backing plates on the Trail-edition pads and the three-layer, two-piece spidered rotors include a layer of aluminum sandwiched between two outer sheets of stainless steel – all in the name of dissipating heat".

[Capricorn]

yes they have, but to what purpose, considering it's on trail-edition pads? Granted, trails can stretch for many miles, but i'm not quite sure the braking it to such an extent as to warrant ceramic + fin-cooling. Maybe it's meant for the brake draggers.

 

but i cant shake this feeling this is more a marketing exercise that says loudly, hey look at us! Definitely, the novelty will appeal to many. I just feel the gains, if any, might just so marginal as not to warrant the inevitable new-ness tax.