Thanks to the folks at Wolf Tooth Components.
These gear charts are for comparing gearing with different front chainrings and rear cassettes for 26″, 27.5″ (650b), and 29″ wheels. Note that a typical 26″ fatbike wheel/tire is very close to 29″ diameter. Numbers are “gear inches” but the actual value does not matter. Rather, it is the relative values than matter. The cassettes shown are 10 spd 11-36 & 11 spd 10-42 (horizontal, gray background). Front chainrings are shown covering a typical 1x or 2x setup (vertical, gray background) These charts are helpful when deciding what size front sprocket to use with a new cassette or when changing from a 2×10 setup to a 1×10 or 1×11.
When selecting a chainring size, we recommend looking first at your lowest gear (smallest gear inches) and comparing that to what you are used to having. Next, look at the top speed available with your largest gear (biggest gear inches) and decide if this is fast enough. For a mountain bike off road, a top pedaling speed in the low 20s is usually more than enough. Max speed shown is assuming a cadence of 100. Also shown is the % change between gears in the cassette.
29 Inch Wheels
26 Inch Wheels
Want to know how fast you will be going in a specific gear and a specific cadence? Find the gear inches value for the front chainring, rear cog, and wheel diameter in the tables above and match it to the closest gearing and cadence combination below.