IB15: Wren’s ultralight ceramic alloy disc brake rotors pass testing, head to market

Will be very interested in real world results. I know one of the reasons stated for the slow uptake of disc on road races is the idea of a pile up full of hot rotors so if they stay at a reasonable temperature and cool quickly, we may see a lot more of them in uci races.

emmm No Centerlock? WTF?

Yes, no sharp edges to micro-warp and make noise on the pads.

@STS
The thermal mass of ceramic is MUCH higher than aluminum or steel, so if you dump a few kilojoules of energy into these rotors the temperature will not go up as high as it would on steel or even ice-tech rotors. This aspect is also why they claim that the 500F test isn’t fair as it likely takes a LOT more energy to get the rotors up to 500F than it would to get a similarly sized steel rotor up to that temperature.

The thermal conductivity of ceramic is typically pretty low, but that’s where these rotors also appear to shine. Not only do they not heat up as quickly thanks to the ceramic, but they can also cool quickly thanks to the aluminum. That means that the rotor will heat remove heat from the pads and sink it into the rotor, which then cools quickly thanks to the conductivity of aluminum.

Plus you end up with a really light rotor.

Win – Doesn’t get as hot
Win – Cools quickly
and
Win – Light weight

Sounds like a whole lot of win, particularly if there’s good friction between the pads and the rotor (as was not the case with carbon rotors like those from Kettle Cycles).

@Matt. Please talk to someone with a degree in physics or any mechanical engineer you know and trust since you won’t believe me when I say that you’re wrong. “Thermal mass” though sounds like an interesting concept ;-).
Mind you, it’s just the coating which is ceramic with those rotors, because otherwise they would not be so light. And if a rotor does not pick up the heat as good as others because of ceramic lower heat conductivity this is actually a bad thing. Because the heat (= converted kinetic energy) has to go somewhere. Better it goes into the rotor than into the caliper, don’t you agree?

@Dirk. Thanks! “but they will dissipate air at different rates into the atmosphere. Take a look at this info on heat in pans.” No, not exactly. The transfer rate of heat from the surface into the air is the same. BUT, the heat conductivity in the material is considerably better (=faster) with aluminum. With a rotor though the whole area which comes into touch with the pads has the same temperature no matter how good the material of the rotor conducts heat because the rotors are turning. Where heat conductivity matters is for the temperature and heat dissipation abilities of the rest of the rotor, the spider. That area will get warmer more quickly with an aluminum rotor. That’s why Shimano’s Freeza rotors have those cooling surfaces made from aluminum extending into an inner layer sandwiched between the braking surface made from stainless steel.
If you ride down a slope with constant radius and you keep your speed the same by dragging the brakes the amount of heat (energy) created per time is constant. The amount of heat being dissipated (=radiated and conducted) into the surrounding air though increases vastly with the temperature difference between the rotor and the surrounding air. Which is a good thing. Real world testing shows though that the point of equlibrum where the amount of created heat equals the amount of dissipated heat lies at temperatures so high that aluminium simply isn’t able to sustain it. That is of course due to the limited space (surface area) any reasonably sized rotor of a bicycle (or motorcycle) disk brake can have.
If you want to have rotors made from aluminum being able to dissipate the heat properly without being damaged they have to be of much bigger diameter than rotors made of steel in order to provide the necessary surface area. Which would negate any weight savings you’re looking for when choosing aluminum for the rotors.

The ceramic coating lowers the heat conductivity considerably. So it might protect the aluminum rotor from getting too hot if you brake only for short times. But as the amount of energy converted into heat doesn’t change, that amount of heat has to go somewhere. Those rotors will certainly rise the temperature at the brake pad. Which is a very bad thing and something that as a brake designer you want to avoid since it increases fading.

@STS, don’t forget that ceramics tend to have higher specific heat capacities than metals. While we don’t know exactly what ceramic is on these rotors, we can say the ceramic coating will allow absorb more energy for a given rise in temperature. Whether that translates to better heat management under heavy braking for these rotors is of course yet to be seen by the public.

We certainly appreciate everyone’s comments, concerns, criticism and defense of our efforts with the new ceramic aluminum disc brake rotors.

First and most important is that these rotors are NOT coated. We select a specific aluminum for our application (thousands of different aluminums available) and blend silicone carbide particulate evenly throughout. It is rolled and flattened before being cut, blasted, anodized and etched.

This is not your father’s metal matrix! For more info visit our website: http://www.wrensports.com
or write me, kevin.wren@wrensportsllc.com