We tried it: BionX v. Stokemonkey

Test riding the stoked EdgeRunner in Seattle. Thanks to Davey Oil for the chance to ride, and Madi Carlson for the great photo!

One of my colleagues recently taught me two great tricks. The first is to never use the word “but” when talking to people because it  always ticks them off. The second was that anything could be summed up in exactly six words. She writes six-word biographies for every graduating student in her program. It is amazing. Given that I am a chronic offender in the Too Long: Didn’t Read sweepstakes, I’ve decided to open all of my reviews with the six word summary. Here’s one now.

BionX: Easy to use

Stokemonkey: Powerful

I’m sure that the respective producers of BionX and Stokemonkey electric assists now wish that they could reach through the screen and punch me in the face. Good thing it’s a virtual world.

There are basically two heavy-hitters in the world of electric assists for cargo bikes. They are BionX, which is a rear-wheel assist (motor on the rear wheel hub), and Stokemonkey, which is a mid-drive assist (motor on the frame running through the chain). The Stokemonkey was out of production for a long time, and now it’s back. I had the chance to try both assists on the same bike, the Xtracycle EdgeRunner, while we were visiting Seattle over spring break, thanks to the lovely G&O Family Cyclery. G&O was the only shop I have ever seen that had both kinds of assists on the same model of bike, which I rode on the same hills on the same day, with both my kids on the back. It made for a near-perfect comparison. The kids ate a few crackers between the Stokemonkey ride and the BionX ride, but still.

I have already written about other brands and types of assists—there are front wheel assists, like on the original Yuba elMundo, and other companies make both rear wheel and mid-drive assists. I’m concentrating on BionX and Stokemonkey because most people shopping for an add-on family bike assist end up choosing between these two, for reasons that center around power and reliability. Both have good odds of hauling a loaded cargo bike around, and they have the reputation of being the least likely to die within a few months of purchase (or immediately after the warranty expires). People who know a lot about electric assists may end up finding or hacking something better. Nevertheless your average rider wants something that does not require the patience and ability to read through and comprehend the forums on Endless-sphere. (Note: when I refer to “pedal assist” here and everywhere else, I am using the EU legal definition, meaning an assisted bike that will only move if you are already pedaling. Although there are other definitions, this is the one that most people I speak with intuit when they hear the term pedal assist.)

BionX

We have a lot of familiarity with the BionX, because it’s the system on our Bullitt. It has served us well, although it is not perfect.

• How much does a BionX cost? $1800 installed by The New Wheel in San Francisco (SF-suitable system with 48v battery)
• How much does a BionX weigh? 14.1 pounds including battery

What I like about the BionX

• The BionX is easy to use. This is a set-it-and-forget-it system combined with a throttle. You can get a boost across intersections by pushing the red button (the throttle), or set a level of assist from 1 to 4 and feel super-powered as you blaze through the city. The pedal assist is the best of any electric assist that I have tried, and I have tried a lot of them now. The BionX was the first assist that I ever tried, and in a way it spoiled me for other assists, because it is truly intuitive to use. There is no learning curve. Anyone who has ever ridden a bike can master it immediately. Many people end up leaving the bike in a relatively high gear and using the different assist levels as gears, and this actually works pretty well.
• It is pretty powerful. BionX systems come in different flavors, and we got the most powerful, with a 48v battery. It works well in San Francisco on our daily rounds, which feature a number of serious hills (Twin Peaks, Alamo Square, Lone Mountain) and various unnamed elevation changes that would qualify as hills in a less topographically challenging city. Families in Seattle, which has less steep hills yet is nonetheless pretty hilly, seem content with the 36v battery system. The cheapest and least powerful systems are probably best for handling stiff winds in areas with mild hills.
• It requires minimal maintenance. There are people who will argue this point. The consensus from the bike shops that we patronize is that they use their assists in a different way than we do. We rarely use the throttle; instead, we use the assist levels to maintain a steady speed and effort level. We do not burn through power trying to race other riders. We have the shop check the wiring every few months. With one major exception, which is that we initially had spokes on the rear wheel that were too thin, which broke by the dozen, the system has not given us grief. We replaced those spokes with much thicker ones and haven’t had issues since.
• It is silent. Lots of assists make a humming noise, or much louder noises. The front wheel assists I have tried definitely sound like motors, and the EcoSpeed mid-drive frankly sounds like a motorcycle. One of the reasons we like riding bicycles is the relative quiet and the opportunity for conversations with our kids, and so the noise of some of these systems was a deal-killer for us. This is not an issue with the BionX. It is the ninja of electric assists.
• It has regenerative braking. This means that you can use the BionX system to slow (or stop) the bike and recharge the battery while going downhill. It is debatable whether regenerative braking adds much to battery capacity—there is loss in any system. In an area like San Francisco, where steep hills abound, careful route planning can actually mean you get some power from the regenerative braking, although this may not apply outside the city. It is inarguable, however, that using the regenerative braking through the motor saves a lot of wear and tear on the bike’s brakes. And it offers me a lot of peace of mind, given that we have had brakes fail in the past. I view the BionX regenerative braking like skydivers view a backup parachute.

What I don’t like about the BionX

• Starts can be slow and difficult. The system is set up to kick in once the bike reaches 2mph. If you are trying to start a loaded bike from a dead stop on a steep hill, you may have trouble getting to that speed. This is particularly the case if, like me, you have a bad leg. Outside of G&O, which is on a moderate hill, I could not get started with both kids on board. I had to walk to bike to a level area. This is evidently something that can be modified—you can reset the controller so that the assist kicks in at a much lower speed [update: as low as 0.5 kph]. Now that I know this, it is high on our to-do list. That modification would help a lot, yet it does not change the fact that no matter what, the initial effort on the start is going to be human-powered. This is our biggest issue with the BionX. It was less of a big deal before I was injured.
• It gives up on really steep hills. There are hills in San Francisco that we cannot get up with a fully-loaded bike—the system overheats, which means it’s back to pure pedal-power at the worst possible time. For people outside of San Francisco, this may be no limitation whatsoever, because SF is the second-hilliest city in the world, also very windy, blah blah blah. This actually turned out not to be a huge deal for us. The system is powerful enough that it can handle most of our trips, and we prefer to take alternate routes for 18%+ grades whether we are riding assisted bikes or not. On the extremely rare occasions where there there is no alternative, there’s always transit or car-share.
• The proprietary battery limits the range. Also it’s annoying. The BionX system is completely self-contained. It’s like Apple computers. You can’t get a battery any more powerful than the battery they supply. You can’t set up a backup battery to extend your range, except by carrying another battery and swapping it in, and their batteries are expensive. There is a big logo on it, which is irritating. However the main issue is that you have no way to control the range other than by picking one of their batteries: you get what you get. The range is not unreasonable, and it handles most of our needs, but there are times when we have to be sure to carry the charger and find a place to plug it in, or suck it up and accept that some of the trip home will be exclusively human-powered. Thankfully that is a much less painful prospect now that we no longer live on a steep hill.
• The system can be finicky.  Matt has dropped two controllers and when you drop them, they break. In one case, the controller seemed to be fine but then the bike started jerking when the assist was on max, because it wasn’t really fine. Replacing the controller costs $100. Argh! The bike shop suggested that we super-glue the third controller in place. There is a certain amount of loose connection hassle with some of the controller parts—the wire to the regeneration system sometimes works loose, and so on. We have the wiring checked regularly and so we haven’t had those problems. I classify this in the same category as our constant brake checks. A certain amount of attention is required.

Stokemonkey

And then there is the Stokemonkey. I’ve ridden a stoked bike for exactly one day, so I can’t offer an opinion that is nearly as informed, and for obvious reasons I have no idea about maintenance.

• How much does a Stokemonkey cost? $1250, not including the battery (varies) or installation ($125 at Clever Cycles in Portland)
• How much does a Stokemonkey weigh? 21 pounds, not including the battery

What I like about the Stokemonkey

• It is incredibly powerful. I would go so far as to say it is virtually unstoppable. The chain or the frame will break before the assist gives out. This is not always obvious when you are riding, because weirdly, it doesn’t feel like it is helping. However I know that the ease I was feeling while hauling 100 pounds of my children up a big hill was not natural, especially with a broken leg. If I hadn’t been sure while I was riding the stoked EdgeRunner,  it became obvious when I rode the BionX EdgeRunner, because it took a lot more effort to get up the same hill. Neither was particularly hard, but the Stokemonkey was definitely easier. I doubt there is any hill that would overpower it. Maybe a vertical wall.
• Starting on a hill is easy. When you push the throttle, the pedals start moving and the bike starts moving. Even with warning, it was hard to be prepared for this. However I had no fear of stopping mid-hill on the Stokemonkey. It cranks right back up to full when you hit the throttle. Starts are my biggest weakness, and so this feature was, for me, the Stokemonkey’s greatest appeal. It destroys all fear of hills. No matter what the incline, it will always start.
• It is compatible with multiple batteries. If BionX is the Apple of electric assist, Stokemonkey is the Windows environment. You can wire any battery into it, or, if you are like me, your bike shop can do it. That is a cost savings, and there is also a learning curve involved—I have no idea how to pick a battery. Any shop installing the Stokemonkey should have a good idea though.
• It is pretty quiet. It is not totally silent like the BionX, and I don’t think that any mid-drive assist could be that quiet, because mid-drive motors run through the chain and there is some noise involved with that movement. I found it unobjectionable. There is one exception to the generally quiet nature of the Stokemonkey. If it is installed on a box bike it will be pretty loud, because the noise of the chain will echo through the box.

What I don’t like about the Stokemonkey

• It is controlled by a throttle only. If you want the assist to kick in, you have to hold the throttle down. It did not take long for my thumb to get sore doing this. I might get used to it over time, but I doubt that I would ever stop finding it annoying.  There is not set-it-and-forget-it option with the Stokemonkey. I’ve ridden enough assisted bikes to know that this is not really workable for us. There are too many hills and too many places where we need to take our hands off the handlebars to signal.
• It is not pedal assist, yet you must pedal. Truly, the Stokemonkey is neither fish nor fowl. When the assist comes on, the chain moves, and so the pedals also move. You have be right there ready to move your legs. Even with warning, I kept whacking my ankles on the pedals on starts because I wasn’t ready for this. On the flip side, when you release the throttle, the pedals keep moving for a little bit on their own, so again, whacked ankles. Personally I found this a small price to pay for instant starts on hills, but still: ouch. Word from people who have stoked bikes is that you get used to this and adjust relatively quickly. In the interim, wear thick socks.
• The learning curve is not insignificant. Using a Stokemonkey was described to me as being a bit like driving a manual transmission car. Amusingly enough this analogy came by way of Davey Oil, who does not drive. Nonetheless it is pretty accurate.  The bike will start to shudder if the Stokemonkey thinks you are in the wrong gear, and then you have to shift down to make it settle. My son, sitting on the back of the bike, noticed this immediately, and he found it both fascinating and disconcerting. “You need to shift, mommy!” In combination with the pedals whacking me in the ankles, it required a lot more attentiveness to the assist while riding than I was expecting. This comes at the price of paying attention to other things, like traffic. With this system I would need to spend time getting comfortable on quiet streets without the kids on board before I would feel confident taking it out on a daily commute.
• The Stokemonkey is only really suitable for certain bikes, mostly longtail bikes. [update: I was wrong, modifications to the original statement follow.] Stokemonkeys are not appropriate for early-model Bakfietsen with roller brakes, or presumably any bike with borderline brakes, because the bike can then get up hills that it can’t safely get down. The mounting of a Stokemonkey is evidently somewhat complicated. This seems to be the case for a lot of mid-drive assists.

The winner: everybody

That was our experience, and to my surprise, it did not feel like a definitive win for either the BionX or the Stokemonkey. I had assumed that when I tried the Stokemonkey I would feel like an idiot for getting the demonstrably less powerful BionX (not that we had a choice at the time) and that I would immediately want to swap out to a Stokemonkey. Although I was really impressed with the Stokemonkey, I didn’t feel like it was a BionX-killer. Moreover, I have no good sense of what I would want when we get a new bike, which for various reasons is on the horizon.

Both systems have strengths and weaknesses, and moreover, both systems can be tweaked/are currently being re-engineered. Grin is working on a pedal-assist, set-it-and-forget-it version of the Stokemonkey, suitable for EdgeRunners only, which [update] has just been released. This resolves my biggest issue with the Stokemonkey (and it means I could probably justify buying an EdgeRunner to myself). On the other hand, resetting the BionX controller to a lower start speed would probably resolve our issues with starts on hills, and San Francisco has a dedicated BionX shop that can handle any maintenance issues. In contrast, getting a Stokemonkey would be a long-distance operation for us. Moreover, BionX is releasing a higher-torque model suitable for super-steep SF hills this year. There isn’t an easy answer. On the other hand, there are no bad decisions to make here either.

In the meantime, I’m incredibly grateful to have had the chance to try both systems on the same bike (which is, incidentally, an awesome bike). Thanks G&O! Thanks Xtracycle!