The values on the chart below can help you compare the granny and tall gears of a 2x10 to a 1x11 set-up for a 29er.
Switching from 20 gears to 11, you'll lose some fine-tuning some of the gears on the top or the bottom end of the spectrum. For example, a 2x10 setup could include 22- and 38-tooth chainrings on the front, and cogs on the rear cassette that range from 11 to 36.
On the gear-inch chart, you can see that a granny gear (22x36) provides 17.7 gear inches of travel. This is a low gear for climbing. A big gear for pushing speed on roads (helpful in tailwind and drafting situations) is 38x11, providing 100.2 gear inches of travel.
If you decide to move to a 1x11 gearing, choosing a non-standard 30 front ring and a 10x42 rear cassette, the granny gear becomes 20.7 inches. Comparing this choice to the 2x10 section on the gearing chart, you'll lose two small (easier) gears.
Also with that 1x11 with a 30-tooth front ring, you'll lose two gears on the top end of the spectrum. Your largest gear becomes 30x10, or 87 gear inches. The largest gear on the 2x10 is somewhere between a 38x14 and 38x12 on a 2x10 setup.
Benefits: For cyclists who want more gear choices and a wider range, consider staying with 2x10 gearing. This will help to optimize cadence and power during longer races.
Do you like to make easy mechanical changes or leave your gearing alone?It's relatively easy to change the front chainring on a 1x11 setup. Riders running this system often have a selection of front chainrings so that they can change gearing to suit course profiles. Some may find all of this changing a hassle, while others find that it is no big deal.
Benefits: With minimal fine-tuning you can change the front chainring on a 1x11 with little mechanical knowledge. Changing chainrings on a 2x10 system isn't as straightforward, though it often isn't necessary due to the larger range of gears.