All wheel drive electric Fat Bike Makes Snow Riding Easier

Using the new Grin Technologies All Axle Hub, this electric fat bike riding in the winter way more fun

 

I just picked up my electrified fat bike from the shop on Xmas eve… and wow, what a difference from the old non-electrified version of this bike.

A lot of people who wonder: “Why an electric bike? Why don’t you just use legpower?”

When it comes to regular bikes, I’ll leave the debate on that subject for another day….

However, with a winter fat bike that’s meant to cover distance, there are very good reasons.

I first got a fat bike a year ago. I bought a not-too-pricey Motobecane Night Train Bullet. I wasn’t sure that I’d enjoy fatbiking, so I didn’t want to invest a lot of money. This was a good bike to get going with – pretty decent components to start, and not such a huge chunk of change as some of the higher-end fat bikes.

I had fun with it, but in the often deep snow here in the mountains of Idaho, I noticed something: it was often a damn lot of work to cover any reasonable distance. Far more work than a mountain bike on a trail.

That’s because even for a groomed trail, the bike with it’s > 4.5” tires, tends to have a lot of friction. And the friction increases a lot more when breaking a shallow trail in the snow. For a few miles of winter riding the bike is good exercise and fun, but going a longer distance (over 5 miles) is a committed affair.

I like to go to the coffee shop in town as my “office away from the office.” It’s “just” a 5 mile ride, but in the snow on a fat bike, it is quite a journey. With the fat tires and all that snow, this bike moves REALLY slowly. I end up spending several hours of my day for the round trip, and that often means I just take the car instead. That’s not what a bike geek like me prefers to do. I want to be on the bike more, not less!

The trouble is that in the snow, I am moving the bike at under 5mph on average. For comparison, on my road bike with all-around tires (gravel and pavement), I typically average 18mph. I talked to a local guy who rides almost every day of the year, and in a recent snowstorm he said he was averaging around 4mph (on pavement!).

This makes activities like commuting into town impractical. While it can still be fun to bike around my local neighborhood, or to occasionally hit the groomed trails, the bike found limited use apart from those things.

Here’s an example: I just biked the 5 miles to the coffee shop in 4″ of fresh (still falling) snow. I was using about 600 watts of motor power on average to maintain 10 miles per hour. That enabled me to make the journey in 30 minutes. Without the electric assist, I was moving at under 5mph. It would have taken me an hour just to get into town, which is too much, since I’m planning on skiing later. The assist allowed me to use the bike, get some exercise, and have a pleasant ride into town, whereas otherwise it would have been the car.

Because of these considerations, I decided last Fall that I needed an electrified fat bike. Electric assist really shines for applications like this, where leg power isn’t enough to overcome weight or friction or distance in practical times for everyday use.

I first shopped around for a pre-built e-fat-bike, as there are quite a few now on the market. However, I couldn’t find one that had the right combination of features and price – plus, I already had a great “donor” bike for a conversion project.

My timing for this was perfect, as the folks at Grin Technologies in Canada had just come out with a brand new “All-Axle” hub motor that would fit the through-axle on this fat bike, without having to swap out major components like the fork. Since I’d worked with them before, I decided to sign up as one of their early beta testers of the new motor, trying it out in the rigors of the deep Idaho snow.

However, one problem I encountered when planning the problem is that all the electric motors and kits on the market have been designed for the old-fashioned bike axles. However, on mountain bikes there’s a new, more durable (and safer) standard for axles that’s emerged, called the “through axle.” While I could have replaced my front fork designed for a through axle with an older-fashioned dropout fork, I didn’t want to go that route unless absolutely necessary. It would have ruined the nice purple color scheme of my bike!

Fortunately, Grin had perfect timing: they’d just developed a lightweight, “all-axle” direct drive hub motor, and they were looking for beta testers. I was one of the first in line!

I sent them an 80-mm Mulefut rim, along with the fork from my bike, and they built up a wheel with a custom adapter plate for the bike. It took a few weeks of waiting for them to take care of the custom work, but it was well worth it!

Installation by a local shop

While I’ve usually done hub motor installs on my own in the past, I opted to have the friendly folks at Gravity Sports in McCall do it this time. I am busy with other things – and one of their mechanics has done several hub motor installs in the past (including his own bike).

He did a clean job of hiding the wiring and getting everything ready to go. For better and worse, Grin produces their e-bike parts with plenty of cable length. This is wonderful when you need it (such as for my electric Big Dummy that I converted last summer), but it does require some creativity in “hiding” the excess when setting up a bike where it’s not needed.

Installing a hub motor like this one is not particularly difficult. However, it does require knowledge of how the wiring goes together, how to install the required (and included) torque arm, and how to mount the other bits.

I picked up the bike just in time for some heavy winter storms. At first, I wasn’t able to ride it because there was a weird stuttering in the motor. After some debugging, I found that one of the phase-wire connections to the motor wasn’t making contact. After fixing it, it was good to go!

Here are a few initial impressions:

All Wheel Drive Makes Winter Biking Way More Practical

One of the big problems with a traditional bike on winter/slippery surfaces is that all the power goes to the rear wheels. The dynamics of how a bike steers makes sending leg power to the front wheel impractical.

Yet most modern cars have front wheel drive for a reason: the pulling action of front wheel drive makes skid-outs and fishtails in the slick stuff less likely.

On a bike, the physics is similar. With solely rear wheel drive, I found in the deeper stuff the rear tire would often auger in, forcing me to get off the bike and walk it forward. On a deeper trail, that would happen often.

In addition, due to the “pushing” action of the rear wheel, if the front starts into a skid, it can be very sketchy to recover and regain control. Once the front tire is in a skid, it acts a bit like a ski with no edge. All steering is lost, unless you quickly “pull up” the front wheel to release from the skid and get it back on track. It can result in going down onto the snow or ice very quickly. I’ve had that happen a few times over the years – it is fast, surprising, and painful.

By installing the electric motor to the front wheel, the bike now has “front wheel drive” – i.e. it pulls forward in whatever direction the tire is being steered. So, while I have still experienced a few moments of slide at the front, it recovers much more quickly as long as I am giving it power to pull its way out of the skid. That alone is worth a lot.

In addition, on the trail, due to the pulling of the front wheel as I get going, the rear has not once “augered in” as it had in the past. It can ride through the deeper stuff far better than with just leg power and rear wheel drive alone.

In early use, I’ve found that about 70%/30% ratio of power front(motor)-rear(legs) seems quite stable compared to either front alone or rear alone. The other day I broke the derailleur hangar by having a misadjusted limit screw that allowed the derailed to shift into the spokes… So, I had to ride about 4 miles back home on icy/snowpacked roads with the front motor alone. While it was still relatively stable with front wheel drive only, there were a few moments where it got a bit sketchy. It definitely works best with a balance of both.

Oddly, I have seen several new fat-electric-bikes on the market, but most are rear wheel drive. They just add to the leg power already going to the rear wheel. After having used this all-wheel-drive version, the idea of a rear wheel drive winter bike seems a bit crazy to me. I suppose for someone who is using the bike where the snow is not so deep or frequent as the mountains of Idaho, it might work out. But for these conditions, all wheel drive is the ticket.

Why the new all-axle Grin motor is so awesome for fat bikes (and probably many other uses)

The other application I use an electric motor for is my cargo bike – an older Surly Big Dummy that I’ve written about elsewhere. For that bike I used an “internally geared” eZee hub motor, which has tons of torque, but due to the gearing, is not entirely silent. A downside of that motor is that it is not possible to use regenerative braking due to the one-way internal clutch.

The new All-Axle Grin motor is a “direct drive” motor – it can use regenerative braking (to charge when you’re going downhill). It is not as torquey as the eZee motor, which for this application is a good thing.

Think about it this way: sometimes when you’re stuck in a car in the snow, the best way to get going is to put it in second gear and start out with less torque. This prevents “spin out” in which case you trade off the higher value for static friction against the lower grip of “dynamic friction” (when the wheel is spinning).

I didn’t want too much torque, but I did still want enough to give me umph as I plow through the deep stuff. I have found that with this set up (running at ~48V), it’s a perfect balance. If I max out the motor, it can still spin a bit on looser surfaces, but if I take it easy, it never spins.

The other things I like about this motor are that it is lighter weight than any other direct-drive motors I’ve encountered (except perhaps BionX, which I believe is similar), and it is silent.

I was concerned about silence, because if I do choose to use it on trails, I don’t want to be making a bunch of noise that might alert people and get the anti-electric crowd up in arms. Besides, I want a clean, quiet experience.

In Grin’s initial blurbs about the new All-Axle Motor, they mentioned that it could be noisy with the standard style controller. That’s because standard motor controllers often use a “trapezoid” shaped pulse to each motor coil. The flat top of the trapezoid can produce harmonics in a motor, and apparently this motor is built with a thin side-shell that can amplify the harmonics. I didn’t want to be “buzzing and humming” down the trails.

Grin recommended a “sine wave” controller to avoid this problem, and just as I was putting this project together, they came out with a new controller that had exactly that. Perfect timing again!

After the motor was initially installed, there was a loud buzzing and stuttering. I became worried that maybe even with the sine wave controller it would be noisy. However, after a little debugging I found the cause: one of the three primary phase-wires that send pulses of power to the motor wasn’t fully connected. Once I got that reconnected, it was perfectly silent.

Silence is Golden – and with my aging ears, I cannot hear anything from this motor whatsoever. Perhaps it has the high-pitched whine that some electrics have, but I cannot detect it.

Why 48 volts?

I got the bike set up at 48 volts, rather than the more typical 36 volts that many e-bikes use. I did this for a few reasons, primary of which is that I already had a 48V, 10 Amp Hour flat eZee pack that uses relatively safe Lithium Manganese batteries. This pack is designed to mount on a rack using Grin’s battery anchor. Not only does it mount quickly to the rack, it can be locked there with a key. It’s a very slick way to have a battery mounted to the rack securely.

 

The other reason I like 48V is having a bit more power than with 36V. I am able to send > 1100W when needed to the motor, equivalent to just over 1 horsepower. This keeps the current at just over 20 Amps. Higher current systems are more expensive, and require larger battery packs.

I have definitely used the extra power going uphill in the snow. Even at the full 1000W, I ascend the local hill in my neighborhood at just 8-10 mph when it’s snowy.

However, for someone who doesn’t have such big hills or deep snow, 36V would certainly suffice.

Pedal assist sensor – the way to go

There are two ways to control power to an e-bike: either using a throttle that’s a bit like a motorcycle, or by having it detect your pedaling and to send power based on that.

With the newer build of my cargo-e-bike I opted for a fancy torque sensing pedal assist system. It works brilliantly, but is not for the budget conscious. I was doing this project on an initial budget, so I opted for a simple pedal sensor that detects rotation, but not torque. These rely on a ring of small magnets mounted to the chainring and/or spindle with an accompanying sensor that detects them as they go by.

Unfortunately, nobody that I’m aware of makes a magnet ring that will fit on an oversized-spindle bike like mine. So the guys at the local bike shop (Gravity Sports in Idaho) are going to modify a ring designed for smaller spindles to fit.

Meanwhile I’m running the bike with throttle only. While it works, I find that long times holding the throttle down make my wrist sore. Maybe I have pansy-ass wrists, but I am looking forward to getting the proper magnet ring installed, so the motor will automatically go in conjunction with pedaling.

What about weight?

The motor itself is 3.95kg (8.7 lbs), and the battery is 3.89kg (8.57 lbs). The rack, controller, and wiring add up to a few more pounds. The bike itself, with tubeless tires, comes in just under 30lbs. The added weight is less than 20 lbs, putting the bike at a total of around 50 lbs. While it is not a super lightweight thing, on a fat bike with an electric assist, the weight is not very noticeable, unless you’re pedaling uphill with no assist.

How fast does it go?

The fastest I’ve had it on the snow-covered roads is about 23 mph. While for a road bike that’s nothing impressive, to cruise along at that speed on a fat bike on the snow is quite a rush. It’s a bit like a snowmobile, but without any of the noise or stinky exhaust. Plus, unlike a snowmobile, you still get exercise as long as you’re pedaling.

At 48 Volts, the motor itself can spin up to almost 50 mph when there’s no weight or load on the bike. The top speed depends on voltage, so at 36V the top speed would be in the high 30’s. On a slick-tire bike in ideal conditions, you might be able to get much closer to these top speeds – or with a higher powered controller. However, with these fat, sticky tires in the snow, I don’t expect to go much over 23 mph – that seemed about tops. It was consuming 1100 watts to maintain that, along with 150 watts or so of leg power.

Custom adapters for a super-wide through axle

Modern fat bikes have been moving to a 150mm wide axle standard. This easily allows for fatter wheels and tires.
The Grin all-axle motor itself is only about 50mm wide, made so that it can fit in older-style narrow axle forks, such as 100mm.

While the motor is set up to accommodate 15mm diameter through axles (like what is on this bike), it was not set up by default for this extra wide configuration.

Grin machined a custom adapter for me that makes it fit perfectly. It sounds like if there’s demand, they may consider making this a standard part.

I’m really pleased how clean the install looks even with the custom adapter.

To wrap up

I am having a lot of fun with this new system! It increases the usability of my fat bike by at least 2X. I have already ridden it more in the few days I’ve had it, than I did in the first few weeks of owning the bike without the motor. It is a true, all-around snow, mud, and ice biking transport machine.

And most importantly, it’s FUN. Traveling at 8-10 mph in the snow without maxing my heart rate constantly is way more fun than traveling at 4-5 mph while pushing myself to the max.

While the electric adds substantial cost (typically $1500-2000), it also adds a lot to the usability and fun of the bike. I’d way rather have a more expensive bike that I use regularly than a less expensive bike that I use once in a while.

Resources and cost summary

To set the bike up, I used the following components:

  • The bike is a Motobecane Night Train 22spd ($1,399). I opted for non-suspension in the front since I mostly use this bike in the winter, and didn’t need suspension.
  • I replaced the stock tires with Vee Snowshoe XL 4.8″ studdable tires, set up tubeless. These have fantastic grip in the snow when run at low PSI (6-8 psi). ($90 x 2 = $180)
  • I used a SUNringle Mulefut 26 inch 32H 80mm rim for the motor build (around $100 at local bike shop).
  • Grin Tech did the spokes and motor build ($92.00)
  • Grin All Axle Motor Hub (Regularly $595)
  • Grinfineon 25A Controller – a great mid-power controller that can be run at 36V or 48V, and has quiet sine wave output ($125)
  • Surly Rear Rack ($140 MSRP)
  • Grin Battery Anchor ($50) and Battery Anchor Clamps ($15)
  • eZee 48V 10Ah Flat Keyed Lithium Manganese Battery Pack with charger ($615) (Note: I upgraded to the Grin Tech “Satiator” charger, which I’ll write about elsewhere. It is a worthwhile upgrade for those who want more versatile charging and longer-lived batteries).
  • The Cycle Analyst E-bike Computer and “brains” ($125) – I find this a necessity as it tells me exactly how much power I’ve used, how efficiently I am riding, and gives much more control over how the bike operates. It can also do a “cruise control” mode.
  • Half-grip twist throttle with e-brake (regen) button ($20)
  • PAS Sensor (12-magnet, $24) – allows bike to go based upon pedaling (requires CycleAnalyst to work)
  • Auxilliary control for adjusting cruise control or Pedal Assist power on the fly ($25)
  • Installation (around $100, depending on whom you have do it)
  • Shipping back and forth to Canada (approx $100)
  • Total approximate retail cost: $3,705 – While not “cheap” by any means, compared to a comparable all-wheel drive bike at retail, this is still quite good.

Disclaimer

While I do not receive any affiliate commission for the links to Grin or others, I do get special deals on Grin tech equipment for my testing and blogging. However, I would NEVER recommend something that I don’t try out and love myself, regardless of whether I get a deal on it or not.

4 thoughts

  1. Awesome breakdown Morgan. Thank-you and Happy New Year! I haven’t seen anything from Cycle9 in a while, glad to see you guys are still moving along.

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