BigDirt, I have looked into this extensively. Most FatBikes with 197mm rear axles need a 74-75 mm chain line. SRAM cranksets usually have 206 mm of Q-Factor. FAT4 cranks have 67-68mm chainline. FAT5 cranks have 75mm of Chainline. SRAM achieves this by using a Boost +3mm (FAT4) chainring or -4mm chainring (FAT5). The -4mm and +3mm nomenclature is counterintuitive … it should really be +4mm and -3mm. Non boost chainrings are -8mm using a more intuitive +or- (or 8mm inboard)
1- Installing a Power2Max Boost PM will give you about 67-68 mm of chain line. To improve your chain line you have a few things to do. This is a bit of hack and you must have a threaded BB for that to work AND an XD cassette driver = you can shift your BB by placing the 2mm spacers between the frame and the BB cup all on the Drive Side. Then you can place a 1mm spacer before you install the SRAM XD cassette. This way you will have gained 3mm bringing that chain line to 70mm. You can also dish the wheel to the non drive side to gain a few mm. THIS IS NOT ideal but it works.
2-Wait for the SRM X-Power dual pedals or get the single one that are currently available. You get to keep the current Q-Factor and cranks BUT you only get 30 hrs of charge. In the cold, it is not uncommon to see 20% of battery life. Not minus 20% ! But 20% total battery life, so that would be -80% battery life. For comparaison, my Stages battery will last about 25-30 hours before I get the Battery Low prompt on my Garmin when it is around -20C or 0F.
3-Get the Assioma PM pedals and do the SPD hack. You will most likely have to chew some of your Winter bike Boots sole… I know this is not a super prospect, chewing off from the $500 Wolfgar Boots is daunting. The UpSide vs the SRM pedals is the 50 hrs battery life that may end up giving you 10 hrs in the coldest of temps.
4-This option is more expensive. You need to purchase a Race Face Crank. Either spindles will work. 30mm or the 24mm. If you go with the 30mm Next or Turbine Cranks you will need the RF189 spindle. If you go with the 24mm Aeffect Cinch Crank, you will need the XCF190 spindle. You then have to purchase a Power2Max Race Face PM. If you choose the Boost PM you will end up with 78mm of chainline. If you choose the non-Boost PM the chainline will be approximately 73mm. The downsides of this change of crankset are the price and the new Q-Factor, you will end up with a Q-Factor of 223 mm (30 mm spindle) or 230mm (24 mm spindle).
5-I know Stages Power have suspended their Factory install program. Maybe 4iiii could do this : I know most fatbike will have some increase crank-frame clearance on the Drive Side. I have not explored is a AAA will clear the chain when using the -4mm offset chainring AND the frame, but that may be worth looking into.
6-One option that you could look into, I know this is not great, but running a 4 in tire in the back will improve chain clearance and prevent chain-tire rub.
I have been running a Stages PM on my fatbike since 2016. I was lucky that it was fitting on my last 2 bikes frames. I made this research for my new Beargrease build coming up next fall. Hope this helps,
