Wheel Drive BBSHD Electric Fatbike

When I was a child I was completely obsessed with Lego. I spent most of my free waking hours in my youth sitting on the floor for hours at a time building anything I could imagine. I distinctly remember one of my creations was an AWD motorcycle with a complex drive system that engaged the front and rear wheels together so that they would spin at the same rate while the fork still swung back and forth. This motorcycle even had a little tiny one cylinder engine with a piston that went up and down. I remember distinctly the joy that building that creation brought me even though it was ugly as sin. When I first heard about Steve Christini’s AWD fatbike that was going to be used for Kate Leemings pedal-powered trip to the south pole I was immediately excited about his bike. I knew I wanted to try it, even if I had to truck down to his shop in PA to check it out. If Steve was going to build an AWD fatbike that could trek the 1850km across Antarctica via the South Pole then I suspected that it might even be tough enough to stand up to my level of abuse. This article is about the two weeks I got to thrash on Steve’s AWD BBSHD powered ebike every day and how I discovered that this bike was nothing like I thought it was going to be.

Before I start talking about my actual experiences with the Christini AWD efatbike I should mention what my expectations were before I first got to ride the bike

• A complex system with lots of moving parts that were going to get clogged up with mud and ice
• Expensive to buy, expensive to get parts for when things break
• Everything was going to be fragile and break easily under power
• Noticeable drag on the bike when AWD system was engaged
• The AWD system would not really make a noticeable performance difference when riding in mud, snow and ice

I could not have been more wrong on every one of these preconceptions about this ebike. On my first ride out I really fell in love with this efatbike and knew that I would eventually probably have to get one for myself (as soon as I win the lottery or pay off my existing debt to the US criminalized banking system).

I experimented with AWD efatbikes several years ago when I threw a 12T Mac motor on the front of my Boris X9 BBSHD efatbike. This setup was pretty marginal because the problem with having a front motor spinning at a different speed than the rear wheel is that most of the time the front wheel would just spin out. That would end up making the ebike even more out of control than it would be if there was no motor on the front wheel at all. When you use a Thudbuster LT with a soft shim it pushes the seat position back several inches which makes the fatbike weight distribution totally off and turning it into a wheelie machine. On top of that having an extra 10 lbs on the front wheel just make for an absolutely awful riding experience. At that point, I had basically written off AWD ebikes as being something that was not worth the time and effort. The incredibly lightweight 2.3lb Christini AWD system really changed my mind about what a real AWD system was capable of on an electric bike.

The way the Christini system works is pretty ingenious. The engagement clutch is near the rear hub which engages the pinion with a large gear that attached to the rear disc attachment point. The power is routed through drive shafts up the body and through several universal joints and into a beveled gear inside the headtube. This then goes down and then is spaced out into the fork and the drive shaft goes down the outside of the front fork and engages with a freewheel gear on the non-disc side of the front wheel. This means when the clutch is disengaged none of AWD the drive system moves at all. It also means when the AWD drive system is engaged and you crank on the rear brakes, the back wheel can skid out but the front wheel can still turn as the freewheel in the front fork allows it to spin at a higher rate of speed than the rear wheel. This freewheel also fixes a common problem with AWD systems where if you turn the front wheel sharply the entire vehicle will ‘jump’ because of different rates of turning on the front wheel (faster turning in a steep turn) vs the rear wheel (which turns slower in a steep turn). The beauty of the Christini AWD system is that you don’t have to know any of this stuff, the bike just works the way it should.

Normally when I ride on the snow with an efatbike like the Phat Phuk I run the tire pressures insanely low and just go out and ride in a very low gear with the motor cadence running much faster than I could ever pedal. The 60 amp Lunacycle Ludicrous controller makes the fatbike a wheelie machine and most of the time I feel barely in control at all. I point the front end where I want it to go, but the reality is that the bike does what it wants to. The back tire is constantly skidding out and the front tire drifts through turns and often will kick out and go in a direction that I really don’t want it to. It’s not uncommon for me to hit trees or end up with the bike completely out of control careening completely off the trail. Good times.