Donkey

20" fat bike from Mongoose (Walmart) I think the Massif is the same bike as the Kong.

Bottom bracket is 110mm English thread

Rear Drop outs are 190mm

Front Drop outs are 135mm

Threaded head tube of unknown size, hair smaller than BMX and other kids bikes I have.

28.6 Seat post shimmed to use 27.2

Cranks are 135mm. Very low bottom bracket and can't go any longer.

Mechanical disc brakes Ok at 150lbs, not safe at 175lbs (a strong person can break them!). I used levers with motor cut. Rear disconnected so one can start on hills. 160mm front 140mm rear rotors.

7 speed with no clutch but works in the rough. Twist grip shift which can be hit accidentally, so gear interrupter installed. 190mm hub with mega range freewheel (34 to 14). 36 tooth chain ring. (42 without fabrication)

Tires on this 100mm rim with 36 holes measure 4.5 inches, not the 4 it says. Usually tires measure smaller. Poor compound, but at really low pressures they work. And yes, we have a paddle tire ready for snow.

The major mod is cutting the bottom bracket and moving that piece to the other side. This is only to get a chain line for a internally geared hub or using a chain ring smaller than 42. Adjusting chain line from the bottom bracket is a god send. A BBSHD on any other bike is always close to the chain stay. Even if you can get the motor on, the chain line can be so bad it will never last. Mongoose has so much room one can cut the BB and get the chain ring closer to center line.

No mod needed when using a 42 tooth chain ring.

Motor:

100mm Bafang BBSHD with stock controller.

Drivetrain;

36 chainring to 7 speed. Gear inches: 23.3 / 28.2 / 33.0 / 37.7 / 43.9 / 56.5 (don't use the smallest cog)

If one doesn't cut the bottom bracket one must use a 42 chainring minimum to preserve the chain line. However with a 42 to 34 the lowest gear inches is 27.1. This will be fine for most people, but under 25 is my goal for extreme hill climbing. And one needs a 120 mm BBSHD, not the 100 mm I used.

Battery:

14s2p of Samsung 30Q

or 52volt 6 amp hours (312 watt hours) 30 amp max draw

can run 2 in parallel with the 2nd battery on water bottle cage

Frank, you built me a mountain goat in just my size: