Running a single chainring setup is getting more and more popular, especially with the release of SRAM‘s XX1 and XO1 groups. Having just acquired a new Santa Cruz Bronson with an XT triple—not my first choice of gearing, it got me curious about all the hype for single chainring (1x) set ups.
I wanted to make my decisions based on science, not marketing hype, so I dug in to the mechanical advantages and disadvantages between running a single ring (1x); vs a double (2x); vs a triple (3x) setup. To figure out exactly what gear ratios were available to me, based on different chainring sizes/combinations, I used Sheldon Brown’s Gear Calculator.
Here are the constants for my ‘experiment’:
Wheel Size: 27.5”/650B
Crank Length: 175mm
10 Speed Cassette: 11/13/15/17/19/21/24/28/32/36
11 Speed Cassette: 10/12/14/16/18/21/24/28/32/36/42
The output of my results are proportionally the same for 26″ & 29″ wheels. A general rule of thumb is to add two teeth to the front chainring for a 26″ wheel and subtract two teeth for a 29″ wheeled bike to get the same gearing listed below.
It is fairly obvious what the change to a double would feel like; a bit wider range than my current first two chainrings (double set ups usually come with a 22/36 or 24/38) while keeping the “weight penalty” of a shifter and derailleur. However, uncovering the gearing of a 1×10 set up is really what I am after.
I am mostly concerned about the low gears because the trails here in San Luis Obispo are steep and I prefer to spin up the hill rather than hammer. Looking at the new 30 tooth Narrow Wide Chainring from Race Face, I determined the lowest gear I could access using the same cassette with a 1×10 set up was only +0.3 difference in Gain ratio from what I can currently access using the lowest gear on my triple set up. Gain Ratio can be explained simply; for every 1 unit of rotation of the crank, the bike will travel X distance.
What does 0.3 Gain Ratio difference feel like though? Using the table below, I was able to determine the lowest gear with the 30 tooth set up would be the same as pedaling my 1st gear in front and #3 in back; see cells highlighted in green. The cells highlighted in red are gear combinations not recommended by Shimano because of bad chain alignment.
For the high end of my cassette with the 30t chainring, the gain ratio difference would be close to riding in middle chainring (2nd) up front and the 9th cog (13t) in back. With this top end limitation I might find myself under geared more often than I would like when I ride my bike to the trailhead.
While the 30 tooth offers the lowest gearing, it also offers the smallest range of gears for single ring set ups. As you increase the size of the chainring, you also increase the range of gears available using the same cassette. See graph & table below.
Where it really gets interesting is the range of gears available with the XX1 group. Looking at the excel tables the 1×11 gearing can give you a wider range of gears than running a double and almost match the range of a triple.
To go to the 1×10 set up, I could keep running the same cranks I have now, and pick up a Race Face Narrow Wide Chainring and some steel chainring bolts, along with a short cage Shimano Zee Derailleur. Then I would get to take off my front shifter and front derailleur. This weight savings comes to about 1 pound. I wouldn’t be running a chain guide because the Race Face Narrow Wide rings are very secure, and I like to live dangerously. This would come out to a total of $164.97. That is a great value to shave a full pound off a bike.
If I wanted to go with a true double to get some added range, I would just need some 2×10 chainrings for about $90, but I would still have the shifter and derailleur weighing down my bike. If I wanted to go all out, I could go with the 1×11 set up. Excluding the 28t chainring, the 1×11 gets a wider gear ratio than the first two chainrings on my triple. To go XX1 I would need a new XX1 drivetrain including:
XX1 Crankset (32t chainring standard)
XX1 Rear Derailleur
XX1 Driver Body For DT Swiss Hubs (because of the wide range of gears on the cassette, a standard freehub body will not accommodate a XX1 cassette)
This all totals up to $1381.94. If I waited till September I could save a few hundred dollars by going with the new XO1.
All in all I think I’ll be going with the 1×10 set up with the 30t ring because of the 1 pound weight savings without sacrificing too much gearing. Most of the gears that I would lose are coming from the 3rd ring which I rarely find myself using anyways.