Every FatBike we carry has at least one thing in common (besides really wide tires): a wider than ‘normal’ bottom bracket.
The wider tires require greater chain clearance so the crankset has to be pushed further out from the centre of the bike to help with this. The standard mountain bike 73mm wide bottom bracket simply isn’t wide enough.
Most new cranksets today have two sides (the driveside that includes the right crankarm, spider, and chainrings, and the non-drive side that includes just the left crankkarm) that are connected directly through the bike frame’s bottom bracket shell by a spindle that’s anchored to the drive side crank. If this is the kind of crankset you’re looking for you obviously require a FatBike specific width crankset so that the spindle can fit through the full length of the wide bottom bracket shell. There are a few options out there; our favourites at the moment are probably made by e.13 and RaceFace, but there are other great options too.
There are however a couple of other options to consider. You can also buy a 100mm ISIS bottom bracket which accommodates the older standard crankset type where both sides of the crankset are bolted directly to the bottom bracket. This allows you to choose virtually any ISIS compatible crankset to mate with your standard threaded FatBike, assuming 100mm is the width required.
You can also look at installing something like the Surly MWOD. Its unique design moves the inner chainring to the middle position, and moves the middle chainring to the outer position (this is not usually possible because on conventional cranksets the inner chainring uses a different bolt ring diameter than the middle and outer). Obviously then you lose the outer (largest) chainring but it means that you have an ever greater amount of chain clearance when in your smallest chainring compared with a regular 100mm set up. This is especially helpful when running tires wider than 3.8″ or so.
Of course you can also create more clearance by using a conventional (i.e. non-MWOD crank) FatBike crankset and removing the inner chainring. The difference between this and the MWOD idea is simply which chainring you’re willing to give up, the inner or the outer.
Or, just to create more confusion, er, we mean to give you more options, you can forget all your chain rub worries by moving to a single chainring set up. With wider and wider rear cassette ranges it’s becoming increasingly attractive to simply run one chainring up front and all but guarantee no chain rub and a decent chain line in all gears while still getting a decent gear range. In most instances we suggest running a chainguide in place of a front derailleur with these set ups to make sure your chain doesn’t jump off of the single chainring.
OR, you can use a Sram 11 speed drivetrain set up made specifically for FatBikes with single chainring crankset that doesn’t require any sort of chain guide to keep the chain from jumping off, or you can do your own single chainring 10 speed conversion that doesn’t require a chainguide (more about that in another post).
So there you go…lots to think about as you build up your next FatBike. Or if you’d rather not think about just let us know what kind of riding you want to do, and a budget, and we’ll offer you some suggestions.