At the top end of professional cycling, performance improvements will always be welcomed if they give riders an edge over the competition. But even the general population will appreciate technologies that reduce the workload as they’re pedalling along.
In a bicycle the main source of inefficiency at present – other than the rider – is the drivetrain. Current chain-drive system efficiency is limited by cross-chaining and the eight points of sliding friction generated from the articulation of the chain, as each chain link engages and disengages when the chain zigzags through the drivetrain and the rotating pulley wheels.
After partnering with the mechanical engineering department at the University of Colorado, bike technology firm CeramicSpeed created the Driven concept, which it says creates 49% less friction than a traditional set-up.
“CeramicSpeed set out to increase optimal drivetrain efficiency to 99%,” says Jason Smith, the firm’s chief technology officer.
Conventional systems such as Shimano’s Dura-Ace drivetrain manage 97.8% efficiency at 380 watt loading and are 97.21% efficient at 250 watt loading. That increases to 98.37% and 98.08% respectively when the system is upgraded with CeramicSpeed’s bottom bracket, oversized pulley wheel system and a specially coated racing chain.
But achieving near perfection in terms of efficiency meant taking a new approach to the drivetrain, not just swapping components.
“The team designed a 21-bearing roller pinion driveshaft system where two bearing pinions provide power transfer from rear to front cog. The pinion driveshaft system eliminates the eight points of chain sliding friction and replaces it with just two points of higher-efficiency bearing rolling friction,” says Smith.
The move to ball bearings is key to Driven’s performance because it removes the sliding friction and replaces it with the rolling friction, making the system more efficient.
The aesthetics of the Driven drivetrain look almost alien compared to what we have come to know as the norm in cycling. There’s no front or rear derailleur or chain. Instead the technology consists of a carbon-fibre driveshaft, a thin, 13-speed, single plane rear cog, a single ring front cog, carbon-fibre pinions and 25 integrated CeramicSpeed bearings.
“The bearings interface with the cog, rolling through the teeth, resulting in zero sliding friction. There is a slight amount of rolling friction; however, two points of rolling friction is considerably less than eight points of sliding friction on a traditional drivetrain,” says Smith.
Smoother shift sought
Engineers at CeramicSpeed with the assistance of the University of Colorado have managed to make a system that is incredibly efficient. But work still needs to be done, most notably on the ability to shift between the 13 gears on the rear cog as smoothly and efficiently as the system turns pedalling force into forward motion. But, given the development team’s achievement with the drivetrain system, you would imagine that’s a relatively simple hurdle to overcome.
The biggest challenge for the Driven system if it’s going to be carried over to real-world bikes is one of integration.
“With the right development, the drivetrain can be carried over to a vast array of applications, from city to triathlon bikes. The challenge is that Driven would need a new type of frame, as it can’t be transferred onto a traditional frame,” says Smith.
Whether or not CeramicSpeed’s Driven technology makes it to the mass market, it proves that there are significant gains to be made if you look beyond conventional wisdom.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.