The Drivetrain That Could Change Everything
You have to see it to believe it.
CConsidering our tiny, lowhorsepower motors, any technical improvement in how much energy gets turned into motion is almost always worth pursuing. So when I saw a concept drivetrain at last year’s Eurobike trade show that claimed to have what would be the world’s highest efficiency, I was intrigued.
Created by CeramicSpeed’s USA office and the University of Colorado Boulder’s Mechanical Engineering Department, the 1x13 drivetrain, called Driven, was the result of a quest by both parties to develop a bicycle drivetrain that could hit a mark of 99 per cent efficiency. In testing, the resulting concept exceeded the goal, according to CeramicSpeed’s chief technology officer, Jason Smith.
The project began with a relatively clean slate. The only requirements were that the system had to use rotating pedals, be adaptable to a somewhat conventional bicycle frame, and employ a standard rear hub. The system that ultimately won out employs a carbon fibre driveshaft with a roller pinion at either end. The pinions engage toothed cogs like a traditional bicycle drivetrain, though Driven’s teeth
are turned 90 degrees from those on a traditional drivetrain.
According to Smith’s testing, a stock Shimano Dura-Ace drivetrain has around 97 per cent efficiency (but can be as high as 98 with some tweaks), and though the almost three-percentage-point difference between Driven and a stock Dura-Ace drivetrain doesn’t seem large, it actually translates to 49 per cent less friction. Smith says Driven’s advantage is that it has two points of roller-bearing friction to a stock drivetrain’s eight points of sliding friction.
But don’t expect to see Driven specced on bikes any time soon. Now that the project’s efficiency goals have been met, Driven’s creators have to figure out the rest of the details before this concept drivetrain can be a legitimate competitor to the traditional chain and derailleur. “The development continues,” said Smith. “We’re working on building a rideable prototype. The goal of this sub-project is to mechanically strengthen the Driven system to withstand rider torque and power.” Meanwhile, the University of Colorado Boulder team is working out how to get the system to shift under load.
While it’s easy to see the chain and derailleur as antiquated and rudimentary, the fact remains: the system has endured many attempts to unseat it. I asked Keith Bontrager – a member of the Mountain Bike Hall of Fame, and one of the brightest engineering minds in the cycling industry – why the chain and derailleur have endured.
“A standard chain and derailleur drivetrain seems wrongheaded, with exposed parts everywhere, clunky mechanisms, and what is on average some obvious compromises in efficiency. But it has evolved with the rest of the bike, and that evolution is complex and subtle. The end result is still fairly durable and reliable – emphasis on fairly – and difficult to beat.”
When asked about Driven, Bontrager said, “I think there will be some significant complications to making the design work reliably in the field. It definitely has promise, and deserves to be finished off.”
Like Bontrager, I want to see Driven finished. I’d find the end of the chain and derailleur era, and the dawn of even more efficient bicycles, thrilling. But it won’t be easy. And it won’t happen quickly.
The chain and derailleur are more efficient than gearboxes and internally geared hubs, the gearing options are almost limitless, they work in many environmental conditions, and they conveniently fit a variety of bike styles, from full-suspension downhill race bikes and tandems to inexpensive road bikes and delivery tricycles. Plus, they’re strong, durable, and light; and easy to clean, repair, and maintain. They’re tolerant of frame and wheel flex and suspension motion.
All of this makes the road ahead that much more difficult for the team behind Driven. But if it does prove to be capable of the same standards of performance as the chain and derailleur, in terms of price, weight, reliability, and adaptability, it could succeed. And if that happens, the magnitude of the achievement cannot be overstated, because the bicycle drivetrain as we know it is already amazing.