Wren ceramic aluminum disc brake rotors

We first spotted Wren Sports’ ceramic-alloy disc brake rotors at Taipei Cycle Show earlier this year, at which time they were still finalizing the shape. Now, they’ve settled on a “drilled” look with anodized center section and let us throw them on the scale.

They’re also in early production and expect to ship 10,000 pieces per month thanks to OEM deals he’s put into place. Founder Kevin Wren says they’ve passed ISO and CPSC testing and will be available on their website soon. Retail is $99 each whether you choose the 140, 160, 180 or 203 millimeter rotors.

The 160mm rotor above comes in at just 65g. Check out weights for the 140 and 180 below, along with technical info on the composite material’s benefits and testing protocols…

Wren ceramic aluminum disc brake rotors

Wren says the EN test requires rotors to go up to 500°F, but those won’t pass that one because the material won’t handle that high of a temperature. But, he says those tests use standards set for stainless steel rotors, not the ceramic aluminum composite these are made of. And Wren says in the real world, these rotors will never get so hot they fail because the material dissipates the heat too quickly. And should you drag it continuously down a long mountain, it’ll eventually warp slightly rather than blow up, giving you an audible heads up that you should pull off and let it cool down. He added that you’d have to go out and intentionally try to trash them to get them to warp…it’s not likely to happen in normal riding.

The newer CPSC protocol tests stopping distance against the amount of pad force applied to it, and he says they pass that one just fine. The ISO test cycles the braking on and off, so it passes that one, too. Those two seals of approval were enough for them to get OE placement deals.

In addition to rapid heat offloading, they claim 50% better wet weather performance than one of the leading rotors, with equal dry weather power.

The 140mm (above) comes in at 55g, and the 180mm (below) hits the scales at 76g.

Wren ceramic aluminum disc brake rotors

WrenSportsLLC.com

15 COMMENTS

  1. 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.

  2. Sorry guys, but this is bs. Where should all the heat go even if the material is able to conduct heat faster? The rate with which heat can be dissipated to the surrounding air does not depend on the material. And rotors actually get much hotter than just 500°F.
    Rotors made from any sort of aluminum alloy are for gram counters only. They are definitely no (lighter but) equivalent replacement for steel rotors which will always be able to store much more heat before it becomes a problem. From my experience with other aluminum alloy, metal matrix rotors you can wreck those without intentionally wanting to within one quick descent of say 1500 feet vertical on a rather steep road with some nice switchbacks which require you to decelerate hard from 50 to 15 mph.

  3. @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).

  4. Interested to see what OE would spec these – I have to imagine, based on the tech/weights alone, these will be 2-3x the price of ice-techs. I’d love to try them, but not if they’re $150+. If they’re not as expensive, they should have 100% of market share in 5 minutes.

  5. @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?

  6. @STS…but they will dissipate air at different rates into the atmosphere. Take a look at this info on heat in pans.
    http://www.chowhound.com/post/measuring-practical-heat-conductivity-cast-iron-aluminum-738175

    Steel is locally hot over the burner, and far cooler out to the edges. As you move into the better conductors (aluminum, copper), the heat is more even throughout and the temperature of the hot spots drops. With aluminum you have more cooling area because the heat gets spread more evenly through the rotor, so you would have more surface area effectively interacting with the air and greater cooling. As well, you could argue that more heat is getting conducted into your hub and rotor bolts. Not sure if that is a good or bad thing.

    Not sure how the ceramic coating would impact the heat flowing into the rotor though. You’re right that the whole point might be moot if all the heat just heads back into the brake caliper.

  7. @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.

  8. @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.

  9. 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

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