The inherent width of fat bikes’ rear tires requires the use of a wider bottom bracket shell, thus a wider crankset and spindle. There are a few options on the market, but brands spec’ing new bikes and those building them up from scratch have a new option from SRAM, the first of the “major” brands to introduce fat-specific equipment.
The SRAM X9 and X5 cranks have been re-engineered to perform on the fat bike. With a 100mm wide spindle and having dedicated SRAM 2X10 chainrings, SRAM has eliminated most tire-to-chain rub often found on fat bikes. The X9 and X5 cranks are lighter than most current fat bike crank offerings and the 36/22 gearing gives riders fast access to the right gear range.
The X5 set will set you back $169 and the X9 set is $314.