VeloNews' 1x vs 2x drivetrain efficiency test and how to do it better

1. "Lennard Zinn theoretically admits and practically neglects chains’ significant impact on drivetrain efficiency. Such an attitude results in the bizzare interpretation of the drivetrain efficiency test: 48/24 chainring/sprocket combo with the straight chainline is less efficient than 39/19 chainring/sprocket combo with 3 cogs off the straight chainline. The best solution is to perform a new test in which 1x and 2x drivetrains with the same chain and the same smallest cog are compared to each other. One of the drivetrain pairs most suitable for the 1x vs 2x testing is Shimano GRX RX810 1x11 vs Shimano GRX RX810 2x11. Or, Shimano could publish its own 1x vs 2x testing which probably has already been done. Why should we common immortals live in the dark?"

That's a good point. Some things to consider:

- This is only one test, I don't know what data other similar (and better) tests would produce/have produced;

- It's not just about speed. Higher drivetrain friction also means higher wear and higher drivetrain parts' replacement costs;

- There are also unprofessional/recreational racers and, more generally speaking, other cyclists to whom marginal gains are important for one reason or another. This group might be considerably bigger than 1% of all cyclists.

Of course, for one who had a bad experience with one's 1x drivetrain and will never put it on one's bike again, 1x vs 2x drivetrain (friction) tests have no practical meaning/value.

The difference is in the chain angles. 1X drivetrains, especially with 11/12-sp cassettes, will always have more extreme chain angles than a 2X setup. Add that crank chainlines have been moved outboard for tire/crank clearance, ignoring drivetrain efficiency, just makes it worse.
I CAN feel a difference in the efficiency, from the size of the ring/cog combos (on singlespeeds and geared) to the same ratios with different chain angles.

I have just one bike with a single chainring, with 5 cogs in back.

gravelest wrote:

Of course, for one who had a bad experience with one's 1x drive train and will never put it on one's bike again, 1x vs 2x drive train (friction) tests have no practical meaning/value.

Zurichman wrote:

. In racing lots of the 2x racers can spin out a 1x rider on the top end.

Zman

I hope you made this comment as a joke.  It’s about the most ridiculous thing I’ve read in a while,  I guess 3x riders would really spin out those those 2x riders on the top end and crush them on steep hills.  I guess no one has ever won a race on a 1x since they are at such a disadvantage.

gravelest

Yes, but the chain angle/chainline is only one part of the equasion. The other one is the cog size – the bigger the more efficient. If you look at the Shimano Ultegra small ring test results (the green dots, see https://www.velonews.com/wp-content/uploads/sites/5/2019/05/Screen-Shot-2019-05-14-at-10.08.29-AM-1.png?resize=1495%2C871) you'll notice that the drivetrain friction keeps dropping after the chain has passed beyond its straight line (39/25). The most efficient combo for this setup is 39/34, which is as much as 3 cogs off the straight chainline. Similarly, the results of the Sram 1x setup show roughly similar efficiency rates (the red dots) as we move from the straight chainline combo (48/18) towards the biggest cog. I have no reason to belive these are only mistakes in the test. In my opinion these show that big cogs do mitigate or, in some cases, even outweight the negative effects of the unstraight chainline.

Titj wrote:Very interesting discussion. 

I just bought a gravel bike, I'll receive it this week. 

I went with Sram Force 1x. Not worried about marginal losses of efficiency because I don't race and when I did some amateur mtb racing 8 years ago, I wasn't taking anyone's place at the top places.

But I think that there are factors that are not being taken into account, even if they are very marginal.

For Instance, can the loss of efficiency caused by a cross chain be compensated by the weight savings on running a 1x system? It's one less lever, cable, derailleur and chainring. 

Also, is there any aerodinamic advantage on a 1x crankset? 

What about Q-factor? Is the chainring on the 1x system located where the inner ring would be on a 2x? It's possible, with dropped chainstays.

Weight has very little affect on power needed. Which dropbar 1x you still have the lever, just without the shifter guts, which should weigh less than a whole flatbar shifter.
Aero, maybe.
Q factor, 1X generally uses a larger ring than the inner ring of 2x and needs to be further outboard. Plus crank chainlines are screwed because of the push for short stays and big tire clearances, even with the dropped stay. Still have to have crank arm clearance.