The metal matrix of most interest to bike folks starts with aluminum alloy. What is added to it is very stiff, vary hard ceramic particles like silicon carbide, boron carbide or aluminum oxide. These additions create very interesting materials.
Steel, titanium and ordinary aluminum are all about the same in terms of "specific modulus," or stiffness as a function of weight. Metal matrix is different -- it can have a significantly higher specific modulus than any of these materials. Because the ceramics included in metal matrix are so hard and abrasive (the stuff mixed into MMC is what sandpapaer and CNC cutting tools are made of), metal matrix is also much more abrasion resistant than aluminum alone. In fact, it can actually be more abrasion-resistant than steel.
Metal matrix is not an all-purpose wonder material. But parts like gears and brake discs take advantage of the one area in which MMCs shine brightest: abrasion resistance. The steel in your chain eats 10-tooth 6061 aluminum gears for lunch -- even the plastic gears that came with your derailleur will probably last longer, because they deform rather than wear away. We think it is a bad idea to make a cheap, disposable part (the chain) chew up expensive, long-term parts (the pulleys). Studies have shown that in the relevant range of forces, MMCs are up to 100 times more abrasion resistant than plain aluminum, and even better than steel in some cases. So Disk Jockeys should outlast your chain, your derailleur -- maybe even your frame.
The biggest problem with MMCs is that they are incredibly tough to machine. Cutting metal matrix with ordinary tools is literally like trying to cut a diamond with a hack saw. Bring a chunk to your corner machine shop and you’re likely to end up with a carbide-tipped stake through your heart. So we had to find a better way to make our cogs. And we did. We don’t want to give away all of our secrets, but we expect to be able to apply what we’ve learned to a few other products soon.
So what happened to the Disk Jockeys and MMC seatposts and stuff?
The Disk Jockeys were a great product, even though they were a royal pain to make. We still think it was the perfect application for MMC. But after trying out our pulleys, Shimano apparently decided they didn't want us playing in their sandbox, and (a) switched to 11-tooth pulley derailleurs, and (b) put a very elegant new bearing design in their top of the line pulleys. It would have cost us quite a bit to retool to go to the 11-tooth design, and since Shimano's product improved quite a bit, it no longer made sense to fight that particular fight.
The seatposts are a different story. We did some instrumented fatigue tests on prototype MMC seatposts. We were not satisfied with what we learned. We didn't want to be responsible for the kinds of injuries that would result from snapped seatpost masts, so we put that item back on the shelf.
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