For at least a couple of important reasons drivetrain and gearing selection is even more important with FatBikes than it is with other types of rides.
First of all you probably want a wider than normal range of gears because you want to be able to choose an ‘easy’ gear to ride through terrain that only a FatBike can traverse while at the same time you’ll inevitably find yourself doing some fast single track, pavement, or even some buff snow that will allow you to slip into as hard a gear as possible and hammer. Unless you’re all about the single speed (more about that further down) at the very least you’ll want a wide-ranging mountain bike cassette with either 10 or 11 speeds. You may also want two or three chainrings up front, but that leads us to the second major considerations for FatBikes: Chainline clearance.
As we’ve mentioned elsewhere chainline clearance is an inherent issue with FatBikes, so some set ups sacrifice at least the inner most (granny) chainring so that the chain doesn’t move too far inboard. Unfortunately this eliminates some of your easiest gear rations. You can overcome this issue somewhat by making sure your middle and/or outer chainrings are smaller than normal, though of course that in turn sacrifices your top end speed. It’s a compromise many people make because you’ll probably do more low speed plodding on your FatBike than you will high speed sprinting.
Newer 1×10 or 1×11 set ups can help mitigate all of these issues. 1×11 set ups from Sram, now available at 3 different price points (but in some cases only as OEM spec) give you a rear cog as small as 10 teeth and as big as 42! Simply select your favourite front chainring and you’re good to go with likely no chainline clearance issues and a wide gear range all contained in the rear cassette, thus simplifying your ride and lightening everything up too.
If you already have a 10 mid level to high end 10 speed drivetrain you can get close to the same range mentioned above by purchasing an aftermarket 40 or 42 tooth rear cog that ‘replaces’ one of your middle cogs, often the 15. This only works with some cassettes though so please ask us what you need if you aren’t certain.
If you have a clutch drive rear derailleur with extra spring tension you may not even need a chain guide up front to help keep your chain from falling off the single front chainring (because you won’t have a front derailleur keeping it on) but for extra security you can in most cases also buy a wide/narrow chainring that does an excellent job of keeping your chain in place in conjunction with the high tension rear derailleur. The 1×11 Sram set ups have high tension RD’s and wide/narrow chainrings as standard equipment, along with the super-wide ranging cassette, so by buying a 40-42 tooth rear cog, clutch derailleur, and wide/narrow chainring you’re essentially building the same set up with one less gear choice overall. The shifting isn’t quite as crisp with this 1×10 set up compared to the stock 1×11, but it’s close and it works well.
Two other considerations: Going single speed or using an internally geared hub. Both options have diehard fans. Both can be set up with frames that are specifically built to accommodate their unique attributes and both have workarounds that make them usable with a lot of ‘non specific-built’ frames. Feel free to ask us about the pro’s and con’s of these additional options.