CeramicSpeed’s concept bike drivetrain, "Driven," grabs attention with its radical looks, and the even more radical claim of better-than-99-percent efficiency. All that attention brings many questions, lots of arm chair engineering, and plenty of pontification (yours truly is no exception).
Here’s the thing: CeramicSpeed doesn’t have a lot of answers yet. Driven is only a concept drivetrain, and one that’s not fully fleshed out. So questions like, "Will it be strong enough to withstand a 1700-watt sprint?" and, "How well will it shift under load?" (and many, many more), don’t have answers yet. And they won’t be answered for a while.
That’s because the main motivation behind Driven was to,"to create a drivetrain that only had one-percent frictional losses," according to Jason Smith, CeramicSpeed’s chief technology officer. The challenge was undertaken by Smith and CeramicSpeed’s USA office, and the University of Colorado Boulder’s Mechanical Engineering Department.
Smith stated that some parameters were put in place at the start: it had to maintain rotating pedals, utilize a somewhat standard bicycle frame, and a standard rear hub. But other than those parameters, the team was free to follow any path.
After multiple attempts, the most promising path was a carbon fiber drive shaft with a roller pinion on each end engaging toothed cogs. The front cog looks like a chaining with its teeth bent 90-degrees, while the 13-speed rear cog looks like the unholy union of a compact disc and the Sarlacc pit from Return of the Jedi. This system showed better-than 99-percent efficiency, meeting the project’s goal, and surpassing the efficiency of the best chain and derailleur drivetrain.
According to CeramicSpeed’s testing, that best-case chain and derailleur drivetrain is Shimano’s Dura Ace enhanced with CeramicSpeed’s Oversized Pulley Wheel System (OSPW), and the company’s UFO chain which returned about 98-percent efficiency (averaged across all gear combinations). A stock Dura Ace drivetrain returned about 97-percent efficiency.
According to the information provided by CeramicSpeed, this means that Driven has 32-percent less friction than the CeramicSpeed enhanced drivetrain, and 49-percent less friction than the stock Dura Ace drivetrain.
The efficiency gain comes from eliminating a chain and derailleur’s eight points of sliding friction. Driven has, "two points of higher-efficiency bearing roller friction," according to the materials provided by CeramicSpeed’s representatives.
A couple percent gain in efficiency may not seem like much to the average enthusiast–especially given Driven’s potential drawbacks and compromises–but racers and performance-obsessed riders would slaughter puppies without a second thought to gain a couple percent.
At this point you probably have many questions; I know I did. The thing is–and Smith willingly admits this–there’s a lot he doesn’t know yet. This project was conceived solely to tease out how to build the most efficient drivetrain. With that seemingly resolved, the hard work of figuring out how to answer all those other big questions begins. But Smith seems very optimistic the the questions can be answered, and all the challenges can be surmounted.
For example: Smith has a mock-up of a shifting system which is comprised of profiled cog teeth, and an electronically-controlled sliding pinion. He pointed out that the flat rear cog would allow better spoke bracing angles, and repositioning the rear disc rotor and caliper, and the hub’s ratcheting driver, from their current locations. There may be weight and aerodynamic advantages as well.
But again, other than the efficiency of the system, everything else is largely unknown. Not only that, the final answers will depend on what steps need to be taken to address all the practical considerations required to turn this into a fully functional system.
There’s reason the chain and derailleur has endured as the dominant multi-speed bicycle drivetrain system: it’s really good. It's light, it’s efficient, it’s pretty simple, it’s durable, and it’s adaptable to a wide range of uses. Many people have tried to improve this particular mousetrap, and most of them have failed. Time will tell if Ceramic Speed has succeeded in finding the answer that has eluded many others for so long.