What electric motor for a fatbike? A practical example.

For the winter of 2023/2024, we decided to build an electric fatbike. We chose the CYC Motor Photon electric motor. Here’s how our winter e-bike for special tasks was built.

Objective: Enjoying riding in winter conditions

Why all this fuss about a fatbike and electric conversion? In this chapter, instead of explanations, we provide a gallery showing at least a glimpse of what cycling in winter is about—especially in mountainous conditions.

So, the question “why” shouldn’t arise 🙂

Plan: Building a winter fatbike with an electric motor

The first step in the entire project was choosing the right base bike, a non-electric bicycle we planned to convert to electric. In previous winter seasons, we rode a Marin B-17 with CYC Motor X1 Pro and X1 Stealth drives. The B-17 is a so-called “plus bike,” which means it has 27.5-inch wheels and a specially designed frame with a suspension that allows the installation of fairly wide tires thanks to appropriate clearances. By “wide” tires, we typically mean those starting from 2.6 inches upwards. However, the possibilities are limited. The B-17 accommodates tires up to 3 inches wide and essentially nothing wider (we used precisely these). Still, for winter, that was far from enough. The bike performed fairly well, but in tougher conditions—like deep snow—it left much to be desired: it bogged down, sank, became impossible to ride, and even the strong motor didn’t help, as it wasn’t about power but traction and grip conditions. And since, as you can see from the gallery, we got hooked on winter riding on an electric bike, for the 2023/24 season, we decided to test how a true fatbike would perform.

Advantages of a fatbike nowadays

Fatbikes had their moment of glory some time ago. It’s rather a thing of the past, unlikely to make a big comeback—especially in its original, non-electric form. Once upon a time, bike marketing imagined that such fat bikes could become a niche worth exploring, and indeed created demand for them. Although not entirely rational, even full-suspension fatbikes began to appear. The fad exploded, and people bought and rode them around the city—more for showing off and individuality than to utilize the actual advantages of such bikes. Back then, in 2018, we had the opportunity to try out an electric fatbike (in mountain terrain, of course) thanks to a bike rental shop from Nowy Targ (E-Bike Podhale). We even appeared with it on the cover of Rowertour magazine in September 2018. By the way, that particular issue generated quite a bit of negative commentary—it was the first cover featuring an e-bike and one of the first articles about e-bikes in Rowertour, stirring dissatisfaction among conservative bikers. But we were simply blazing new trails 😉

Nevertheless, the fatbike category declined in popularity almost as quickly as it rose. Today, it has a small group of supporters, primarily among enthusiasts of distant, exotic expeditions with panniers. But the development of electric technology seems to be giving fatbikes a new lease of life—a second chance. Why? Due to their design, fatbikes require a significant amount of energy to ride, not because of their weight (fatbikes are actually lighter than enduro mountain bikes), but because of the tires and the very low pressure used while riding. The tires are supposed to stick to the surface and roll over obstacles, which creates significant rolling resistance. And here, a relatively young trend—electric bike conversion kits, particularly mid-drive kits—comes to the rescue. An electric fatbike removes its primary disadvantage: the heaviness of riding. An electric fatbike once again becomes a bike that can easily take you almost anywhere—especially through mountainous terrain, sand, or deep snow, areas unfriendly to other bikes. This, in our opinion, is the new niche. Electric mid-drive kits like the CYC Motor X1 (Pro and Stealth) or Photon series offer unprecedented possibilities because they can be easily swapped between bikes. It’s easy to imagine a scenario where in summer the same motor powers our enduro bike or assists us on a gravel bike, and in winter we use it in a fatbike. Swapping between bikes takes no more than 2-3 hours. Moreover, the CYC Motor kits are so cleverly designed that changing just a few components allows the same motor to fit a completely different frame, and sometimes no component changes are even necessary.

Searching for the base – an almost perfect fatbike

A new fatbike isn’t cheap, mainly due to low popularity and limited demand. Anything rarely bought tends to be pricier than it could be with mass production. An electric fatbike, in particular, would be extremely expensive. However, on the second-hand market, the situation appears completely different. Due to low interest, non-electric fatbikes sell for surprisingly reasonable prices. The best part is that they’re usually in very good condition, typically being a second or third bike used sporadically. Thus, they tend to have low mileage and excellent condition. We chose this option—not buying a new fatbike, but looking for a used one. Our goal was a high-end model (no cheap supermarket or Chinese bike-like products), without suspension and necessarily with a single front chainring (1x drivetrain). Why? Because electrification with a mid-drive kit involves installing only one front chainring (we eliminate the front derailleur, if the original bike has one). Consequently, it’s recommended that the bike has a wide gear range in the back. Only a 1x drivetrain offers this. Equally important to us was the width of the tires that could be installed, ideally already having the widest possible tires fitted, as replacing fatbike tires can be very expensive. This is one of the drawbacks of fatbikes: good, wide tires cost more than car tires. Eventually, we found a bike equipped with 4.8-inch tires—a Felt DD 30 in excellent condition, almost like new, for 1,000 EUR.

The specifications of this nearly perfect fatbike are as follows: rigid frame, rigid fork, thru-axles, 26″ wheels, 4.8″ tires, plenty of clearance for mud and snow, tubeless-ready rims, a 1×11 drivetrain (rear cassette range 11-46T), hydraulic brakes, and an interesting bonus: a carbon handlebar. Weight: 14 kg and fairly decent, modern geometry (2020 model). So why is it “almost perfect”? It definitely lacks a dropper seatpost!

Tip 1: For an e-fatbike conversion, look for a bike with a 1x drivetrain, offering a wide range cassette.

Tip 2: Choose a bike with wide tires (preferably 4.6″ and above), or at least one that allows for the widest possible tire installation. 26″ wheels are preferable, as tire availability is better.

Tip 3: Look for a bike with a threaded bottom bracket (not press-fit) with a width of 100 mm or 120 mm.

Choosing an electric motor – why CYC Motor Photon?

Choosing the electric motor for this bike was straightforward. Firstly, we wanted a modern, durable drive with a torque sensor, a small front chainring, and low weight. Secondly, we prioritized quiet operation. Thirdly, we didn’t need excessive power but didn’t want to limit ourselves to just 250 W. Finally, the drive had to be weather-resistant and well-sealed. The CYC Motor Photon meets all these criteria. Kits like the X1 Pro or X1 Stealth are unnecessarily powerful, loud, heavier, and more expensive. Moreover, their design is essential for full-suspension bikes, where the shape of the down tube often requires the motor to be offset from the bottom bracket axis to maintain ground clearance. In a hardtail bike with an upward-sloping down tube, this isn’t a concern, even with the Photon. Additionally, the Photon has a power of 750 W, peaking even higher. It’s quiet, lightweight, easy to install, and, importantly, comes standard with a smaller chainring (34T) providing good chainline alignment. It supports various battery voltages (from 36V to 52V), includes a torque sensor, and has an app for programming assistance parameters. All these advantages made the Photon an obvious choice. Competitors like Bafang or TSDZ2 Tongsheng motors don’t offer all these features simultaneously.

Tip 4: For converting a rigid fatbike to electric, choose the CYC Motor Photon. Use a suitable bottom bracket for your frame and select the smallest possible chainring—in this case, 34T.

Installing an electric motor in a fatbike

As mentioned earlier, installation is generally straightforward. However, in our case, we encountered two minor issues—though it might be more accurate to call them “aspects” rather than problems, as they required thoughtful consideration rather than complex solutions.

The first was the fact that even if we wanted to install a chainring larger than 34T, it wouldn’t be possible without negatively affecting the chainline—meaning shifting the motor to the right. Moreover, such shifting might not have been feasible due to axle length limitations. Simply put, the shape of the rear triangle of our frame wouldn’t accommodate a chainring larger than 34T.

The second aspect was an interesting puzzle—the bike had a 100 mm bottom bracket shell width, yet the axle length was appropriate for a 120 mm bottom bracket. It turns out the bike indeed supports a 120 mm bottom bracket, using spacers to fill the extra space. When installing our drive, we chose the 120 mm version and utilized the original Felt spacers. The 100 mm Photon version would have been too narrow, with too short an axle. The 120 mm kit doesn’t include such spacers because the assumption is that you don’t need to compensate for an extra 20 mm. The worst-case scenario would have required manufacturing (turning or purchasing) suitable spacers, but fortunately, we could use Felt’s original ones. In our case, the resulting Q-factor was 240 mm (just 10 mm wider than the original Felt), and the chainline was ideal—the front chainring aligned perfectly with the center of the rear cassette.

Another potential issue is the speed sensor. The magnet placed on the spoke needs to be close enough to the sensor mounted on the rear frame stay. In a fatbike, these distances can be significant. However, the CYC Motor sensor is extendable and quite long, with good sensitivity, so in practice, it’s possible to mount it so that the sensor reliably detects the magnet, giving the controller accurate information about rear-wheel rotation.

During installation, we omitted the throttle. We don’t use it, making it unnecessary clutter on the handlebar. The connector should be protected against water ingress, or you can buy a cable without the 1-to-2 split for display and throttle (the 1-to-1 control cable harness) to eliminate the unnecessary connector entirely. In the app, you can simply deactivate the throttle. Of course, you could retain the throttle if you prefer, as it can help with starting in difficult terrain or when walking with the bike. Even without the throttle, walk-assist mode is accessible from the display buttons.

Tip 5: When selecting the motor kit for your bike, don’t rely solely on the manufacturer’s specification of bottom bracket shell width. Also, consider actual measurements—particularly how wide apart the crank arms (Q-factor) are.

Bike weight after installation as shown in the photos: 18.20 kg.

Battery

We’re quite consistent regarding battery choice. For years we’ve preferred carrying the battery in a backpack. In this case, the battery also sits on our back. It’s a flat-shaped pack, distributing weight well across a larger surface area. The battery has a 48 V voltage, a 720 Wh capacity (13s3p pack), based on LG M50 LT cells, with a continuous discharge current between 25 A and 30 A. We specifically commissioned this battery configuration because we prioritize capacity over maximum current and power. In this configuration, the maximum continuous theoretical power output ranges between 1,200 and 1,500 W, which is safely more than enough for powering the Photon motor. As a result, the battery operates within optimal current parameters, which should positively affect its lifespan and reduce capacity deterioration over successive cycles. For charging, we use a 3 A charger—it’s not exceptionally fast, but it doesn’t negatively impact the cells during charging.

A battery that’s not permanently attached to the bike has the advantage of being easily portable, meaning you simply take it with whichever bike you plan to ride. There’s no need to have as many batteries as bikes equipped with motors. When switching the motor between bikes, you also don’t need to worry about battery mounting, making the whole process much simpler.

Battery weight with cable: 3.15 kg

This battery provides quite good performance off-road regarding range and total vertical climbing. In winter conditions, it’s beneficial to have extra battery capacity to avoid surprises or rapid discharge while out riding.

Read our article about battery range in summer conditions: click here

Cost of building an electric fatbike

Option 1

If you’re building an electric fatbike from scratch, similar to our setup, the costs are as follows:

• Base bike (used fatbike): ~1,000 EUR
• CYC Motor Photon kit with 34T chainring: 1,400 EUR
• Battery: 500 – 700 EUR

Average total: ~3,000 EUR

Option 2

Assuming you already own a CYC Motor Photon that you’re using on your “summer” bike, to convert it to a 120 mm fatbike version, you only need a longer axle, a longer left-side bottom bracket component, and mounting hardware with spacers.

Total cost is just over: 120 EUR.

Below, on a white background, is the standard flat A-frame with spacers for bottom brackets ranging from 68 mm to 100 mm—this is the support element on the left side of the Photon motor body. In the installation photo, you can see the offset A-frame used for the 120 mm version.

Summary

The CYC Motor Photon is an electric motor (mid-drive kit) that is ideal for building an electric fatbike. It’s compatible with the wide bottom brackets used in fatbikes. The Photon drive is durable, weather-resistant (snow, moisture), quiet, and allows for the installation of a relatively small chainring, maintaining a good chainline (the smallest possible chainring is 34T). This is beneficial for off-road and mountain riding conditions, typical for fatbike use. A fatbike isn’t about speed but about tackling challenging terrain and soft surfaces.

You can easily use a CYC Motor drive that you already own from another bike. For the winter, you can quickly adapt it to a fatbike and transfer it between bikes.

Personally, the biggest advantage I find in an electrified bike for winter riding is that it makes riding in such conditions significantly safer in terms of health. I refer to something I call “body temperature equilibrium.” Riding a traditional bike in winter causes significant fluctuations in body temperature—during uphill climbs or when struggling through tough terrain (e.g., deep snow), you can become overheated and sweaty. Meanwhile, during descents, you risk getting extremely cold. With an electric bike, I dress warmly, avoid intense exertion and overheating on climbs, and don’t get cold on descents. Thus, the risk of catching a cold is reduced, and the comfort of the entire ride increases significantly. Additionally, instead of battling exhausting terrain and snow, I focus primarily on balance technique and simply having fun in the snow. This makes winter rides much more appealing, and familiar summer trails become something entirely new and fantastic. I genuinely recommend winter biking!

Below is an instructional video showing the Photon installation process on a standard bike with a threaded bottom bracket width between 68 mm and 83 mm.