Update: Bafang is selling a new 68-120mm BB BBS02 1000W drive unit which should be available soon. Check out this link for more info.
In many ways the BBS02 is the king of mid drive units. Being the most affordable and easily installed on a wide variety of bike frames the BBS02 fails on many fronts when it comes to being installed on fatbikes.
Most fatbikes have a much wider Bottom Bracket than the industry standard 68mm. Fat bike manufacturers have mostly standardized on the 100mm BB so the chainline can still not hit the tire in the lower gears. There is no easy way to get a stock BBS02 to install on a 100mm BB. That being said where there is a will, there is always a way. Here are some options for installing a BBS02 on a fat-bike.
1) The easiest and simplest option is to buy an already converted BBS02 from Doug at California Ebikes for $1299 + $35 S/H. Doug’s unit was the first to market, and he is the only one who sells a toolkit and modification package so people can do the axle swap themselves (see step 5).
2) Chris at Lectric Cycles just released a 100mm BBS02 drive unit under the e-Rad name and the 750 watt unit sells here for $1200, about $99 less than Doug’s unit. The e-Rad system also comes with a lot of extra stuff for free like a BCD chain ring adapter ($50 value), a RaceFace Narrow Wide Chainrings ($50 value), and your choice of universal brake sensors ($50 value) or mechanical brake sensor levers and your choice of gear sensor ($100 value). The gear sensor is hooked to a proprietary e-Rad only extra Higo plug that uses custom firmware for perfectly timed motor cutoff when you shift. No other BBS02 drive system on the market as of yet has this feature.
3) Roshan at Biktrix in Canada has also released a 100mm BBS02 kit both as a completed drive unit for $1350 USD (750W) and as an add on axle kit to an existing BBS02 unit for $350 USD. I have tested this unit for several weeks and the entire review can be found here.
4) You can buy a fatbike with a 100mm BB and grid it down to <70mm wide with an angle grinder. Some fatbikes have a BB that has enough clearance around it to mount the BBS02 if the sides are ground down. This can be problematic as sometimes the pictures of the bike they post online have a different configuration than the pictures they post online. This picture was for a Bullseye Monster from Bikes Direct, but when I purchased the bike and it arrived the BB looked totally different and could not be ground down without cutting into the chainstay.
5) Purchase a singlespeed Deadeye Monster fatbike from Bikes Direct or an 7 speed Dolomite from Walmart which both have the industry standard 68mm BB. It is likely that you will need to find offset crankarms to clear the chainstays. To create multiple speeds on the Deadeye you can install an internal geared hub or CVT like the Rohloff or Nuvinci. Be aware that some geared hubs cannot take the power output of the BBS02. The N330 is only rated for 60Nm of force but the BBS02 can deliver 120Nm of force, a N171 is a much better option if you can find one as it is designed to withstand 120Nm of force.
6) Purchase a modification package from Doug at California E-bike and modify your own BBS02 to 100mm. This modification package does not require any special milling tools and can be done in any decent bike shop. The modification package is $499 plus $35 S/H available here and the tool package for doing the conversion is $345 plus $35 S/H found here. If you only want to do one conversion you can return the tool package for a $300 credit, but you must specify that when ordering the package. The video for how this is done is found here.
Installing a geared or direct drive hub (Mac, BPM or 9C) motor in a fatbike can be a daunting task. Although you can easily mount a rear hub (135mm) into the front wheel of most fatbikes (which tend to be 135mm spacing) having a front wheel drive fatbike is a total wast of time. There is just not enough weight in the front to make it have enough traction to have a good time with. Dealing with Non-standard hub spacing and having to build up the hub yourself with a custom 36H fatbike rim (most fatbike tires are 32 Hole not 36 hole which almost every hub motor is 36 hole) is time consuming and expensive. Unless you end up with something in the 2500+ Watt range most people will end up being disappointed at the performance of hub motors installed on fatbikes. In my opinion due to the massive size of the rear tire on a fatbike (about the size of a 29er tire) you will never have enough torque and power out of most any hub motor you can find on the market today. The only way it would work well with a hub motor is if you were using a much smaller tire (like a 20″ fatbike tire).
With just a little extra effort you can mount the king of middrive units to almost any fatbike and have a grin permanently attached to your face.