Friction differences between 1X and 2X drivetrains

Single-chainring (1X) drivetrains are de rigueur for mountain and cyclocross bikes, and it’s easy to see why. These drivetrains require fewer overall parts, which decreases cost, weight, and even aerodynamic drag. The single shift lever also simplifies gear shifts.

But do these innovative drivetrains produce more or less friction than traditional ones? We set out to discover the answer. One might assume that a 1x system is more efficient due to the fewer number of parts. There are other dynamics at play, however, in this equation. The more a chain moves laterally, the more friction it produces, potentially giving the upper hand to a traditional 2X system.

For our test we used the labs at CeramicSpeed USA in Boulder, Colorado. CeramicSpeed’s chief technology officer Jason Smith conducted the tests; Smith founded FrictionFacts, a friction-testing laboratory acquired by CeramicSpeed in 2014. Smith has developed precision equipment for testing drivetrain efficiency, and uses it to measure how many watts of a rider’s power are lost within a bicycle’s moving parts.

Let’s take a closer look at our test methods and the final results.

Test protocol

The 1X setup comprised a SRAM Force 1 rear derailleur, 48-tooth X-Sync narrow-wide-tooth (NW) chainring, PC-1170 chain, and 10-42-tooth cassette. The 2X drivetrain included a Shimano Ultegra rear derailleur, 39-/53-tooth chainrings, CN-HG701 chain, and 11-34-tooth cassette. We simulated a rider output of 250 watts pedaling at a cadence of 95RPM with both setups, and used the same total gear range.

We ran both chains on the test machine for the same time, then stripped away the factory lubricant, and re-lubed them with additive-free mineral oil. We selected cogs to create the approximate same gear ranges for both setups.
We measured the chain-line on each setup as well as the amount of lateral offset in every non-aligned gear combination. The 1X chainring was aligned with the fifth from smallest cog. The 53-tooth chainring of the 2X drivetrain was also aligned with the fifth from smallest cog, while the 39-tooth chainring of the 2X was aligned with the eighth from smallest cog.

Results

The 2X drivetrain had lower frictional losses in every gear than the 1X system—with the caveat that the chainrings matched up with the ideal cogs in the rear. The average friction within the 1X drivetrain was 12.24 watts. This was computed as the sum of the drivetrain power losses in each of the 11 gears divided by 11. The average friction of the 2X drivetrain was 9.45 watts, computed as the sum of the power losses in each of the 15 optimal gears divided by 15. This is just under a three-watt average difference between the two drivetrains.

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