If you live where it snows in the winter, or where its rainy almost all the time, or…you live where there is a lot of sand…you may want to know how to get the maximum traction in these less-than-ideal conditions. This article is how to achieve that, by using a 2WD fat bike.
We have written about 2WD electric bikes before, and we have also written about E-bikes with very fat tires. We are just now starting to see a few retailers make a 2WD fat bike available to the public, and even if it almost impossible right now to find one for a test drive, it just makes sense that this is simply the best way to get the maximum amount of traction in poor road conditions.
Two Wheel Drive (not necessarily a fatbike)
The first 2WD E-bike that we wrote about was from our friend Zlatko in Croatia. He was fond of the board-tracker race motorcycles of the 1910’s, and he decided to make an E-bike with that style. Although the battery pack is not stealthy, he wanted to use two small hub motors because they looked similar to the drum brakes of those classic early motorcycles.
In spite of how small the hubmotors were, the system proved to be quite powerful because there were two of them, which provides twice the copper mass for absorbing amps. Also, it is obvious now that it also doubles the traction of the bike because two tires are pulling instead of just one. This is no small feature. If you have one large hubmotor using a lot of watts…the E-bike is often able to do a burnout. That can be a lot of fun for a few seconds, but…if the tire is spinning out, the bike is not accelerating.
The next 2WD E-bike we wrote about was also from the electric bike chat forum “endless-sphere”. It was built by our friend Alan, and his use-name is Teklektik, and he is an electrical engineer who built a longtail cargobike that could replace his car (when the weather is nice). He used a Yuba Mundo as the base frame, and thoroughly researched every component. His decision to use two medium-sized geared hubmotors had more to do with redundancy than being able to use two smaller motors like Zlatko (which would add up to the power of one larger motor). If there was ever a problem with one of the controllers or motors, Alan could still get home on the other set.
The most recent 2WD E-bike that we have featured is from our friend Ben. He wanted a full-sized folding E-bike to be able to take it on a train for day-trips into the beautiful local mountains of Taiwan.
Although Ben appreciated the aspect of having two separate systems for redundancy, the steep roads where he lived convinced him that he needed maximum traction, after his single motor E-bikes occasionally had the tires spin out. He also decided (just like the other two) that there was a significant benefit to having a geared hubmotor in the front, because they freewheel (as opposed to the slight drag that a direct-drive hubmotor experiences from cogging)
He also decided that it would greatly simplify many things if he used two identical systems, so he chose dual MAC geared hub motors from em3ev.com. Alan’s Yuba used two BMC geared hubmotors, and those two models (the MAC and the BMC) are almost identical. They are the largest geared hubmotors that I know of. Each has a 22mm wide stator, so two of them have 44mm width of copper mass in the electro-magnets…which is almost as much as the monster Cromotor.
Here’s a late edit. I had forgotten about our friend kingfish. He wanted to take an epic 1,000-mile ride, and decided he could use the redundancy of 2WD. Here are the details of that build.
If you read these four articles, we can learn from their experience. All four used:
A) Two identical systems.
B) Geared hubmotors, which freewheel with no cogging when unpowered.
C) One throttle, two controllers, and two motors.
D) Two torque-arms on the front hub motor, and at least one on the back.
Now, bear in mind, the fact that two medium motors can provide the same power as one large motor also means…that they can draw as many amps as a large motor. This means you have to use a high-current battery to get the full benefit of 2WD. Here is an article on high current batteries. Its true that this battery article is a year old, but the information is still accurate, and em3ev.com is still our number one recommendation for a battery pack that can provide 40A of continuous current (20A to each motor).
If you want to buy a 2WD E-bike instead of build up a custom project, you can get one that puts out 5500W (using two direct-drive hubmotors that are ventilated) from Hi-Power Cycles / HPC for $6,995
Fat bikes have been the hot trend for 2014. They were just an oddity in 2013, but this last year they have really established themselves. Their looks are deceiving, because even though they appear to be heavy, they are often used in applications where the plush ride provided by the plump tires means that a smooth ride can be had without the weight and cost of front and rear suspension. Keep in mind that even though they do have more rubber in each tire (and a wider aluminum rim)…the bulk of their size is just extra air.
The most common size of tire seems to be 4-inches wide, but the industry also seems to allow any tire to carry the “fat bike” title if they have tires from as narrow as 3-inches. But the fat tire label doesn’t stop at 4-inches, they can be found all the way up to a massive 4.8-inches wide. I do agree with several bicycle industry insiders that there is some temporary interest in fat bikes because it is the “trend of the year”, but…after the initial hoopla has died down, I think they will prove to be resilient in those applications where they simply perform better than bikes with common-sized tires.
[Take note that fat rims and tires are also now available in 24-inch and 20-inch sizes. A 24-inch wheel with a 3-inch tire will have the same outer diameter as a 26-inch wheel with a common 2-inch tire]
This means that fatbikes should remain popular on sandy beaches and deserts where skinny tires will get you nowhere. And even if that is quite a small niche market, they are also the absolute best solution for a bike in snow. Now…you may be thinking that only a crazy person would ride a bike in snow, when they could be relaxing next to a fireplace indoors. Maybe that’s true, but there are a lot of people living in Canada, Northern Europe, and Russia. In those places, if you don’t go out when there’s snow…you will end up stuck indoors for about six months!
The last thing I want to say about fat bikes is…forget about all the logical reasons I just listed, the bottom line is that these things are just so much damn FUN! People who test ride them…they like them.
Before you start wondering if there are enough choices to have a decent selection of fat bikes, the web-magazine fat-bike.com lists 66 manufacturers! (and these manufacturers often have several fatbike models each). Speaking of fat-bike.com, here is their Facebook page.
Our friend Karl has a new blog that is specifically about electric fatbikes, check it out for all the latest new info that comes out about these.
We knew this was a great idea, but we also knew that we weren’t the only ones who thought of that. Way back in October of 2012, endless-sphere forum member “sgds23″ in San Francisco had already built a 2WD fatbike.
– 9:zero:7 titanium frame (170mm rear dropout width)
– Carver carbon fiber fork (130mm)
– BMC V2T in front, Crystalyte X5403 in back. Two 40A infineon controllers.
– Shimano XTR hydraulic brakes (180mm Avid rotors)
– Surley cranks
– Weinmann 65mm wide rims,
– Surly Black Floyd 3.8-inch tires. Two tubes in each wheel for failover protection.
– Platform-1 pedals, controltech crossbow carbon handlebar, ergon seat, thudbuster, etc…
“…First, I replaced the X5304 motor in the back – it was just too damn heavy – with an HS3540.
Ah– I’m back in love with my bike, thanks to LiPo. I had been using a 50V / 10-Ah LiMnCo battery from batteryspace which seemed solid, but only put out 30-amps continuous/40-amps burst.
I didn’t realize how much that was holding me back until I bought two 7s 11,000 mAh LiPos from MaxAmps, supposedly rated at 40c. I’m not sure if these batteries are actually capable of putting out 200+ amps, but my bike’s performance says it’s close. The bike now pulls faster than I can hang on, I’ve had to modify my controller code to moderate the acceleration right off the line. At 14S X 4.10V per cell when fully charged, the pack is 57.4V, and this bike can do 40-MPH…”
By having a direct drive (DD) hub motor in the rear wheel, this bike is able to use the rear motor as a “regen brake” on the steep downhills of San Francisco. The mounted dual disc brakes work quite well, but using the controllers regen function (where the motor temporarily functions as a generator) keeps the disc brakes cooler than they would run otherwise.
Dunesday HPC Bigfoot, 2WD Fatbike
When HPC first started out, they were known for making some outrageous claims in their ads. I wasn’t sure if they would survive even a year. Its been several years since then and they are still around, and…I can’t help but to notice that their ads are slightly less wild, compared to before.
I mention them because they just recently began producing a 2WD Fatbike for sale to the public, which they are calling the “Dunesday”. They are claiming 10,000W total, so the battery is almost certain to be LiPo. We know that LiPo batteries perform well, but they must be handled and charged with caution.
Human Electric Hybrid / HEH, 2WD Fatbike
Just found this, so I’m adding it right away. HEH in Michigan (lots of snow there!) will make a 2WD fatbike using the Motobecane FB4 Fantom frame as a base, and combining two Crystalyte H35 hubs. The 48V system provides 42-MPH. That would be a sketchy claim with one motor, but two of them can use a ton of amps, so the numbers do add up.
The real standout feature for this 2WD Fatbike is the price and the size of the battery. It uses TWIN 20-AH battery packs for high-performance and long range…and they’ll build you one of these for $6299 (tax and shipping extra).
Here’s a hot edit: HEH will now make their 2WD fatbike bits available in kit-form, but contact them to make sure their bits will fit the frame you want to use.
Building your own E-Fatbike
I don’t know of any fatbike kits yet (new info, see below), and I especially don’t know of any 2WD fatbike kits. If you don’t want to pay the retail price of a Dunesday, you will have to buy the components and have a bicycle shop lace the wheels. The most immediate problem is that most fatbike rims have 32-holes for the spokes, but most E-bike hubmotors have 36-holes.
Once I knew that, it narrowed down the choices rapidly. I found several 36H fat rim choices, but only for a 26-inch tire:
Blunt-35 mid fat rim, this will accept only up to a 3-0-inch wide tire
26-inch, double-wall, 36H, no eyelets, disc only $109
26-inch, 36H, 559 X 73mm, 830-g, pinned joint
26-inch, 36H, 559 X 76mm, 850-g, welded joint
26-inch, 36H, 559 X 82mm, 860-g, disc only
These guys have a selection of fat rims using 36H
They also have fat rims in 24-inch, and 20-inch diameters (along with the common 26-inch)
• Plus tires (2.7 – 3.0˝)—Designed for use with rims 35 – 65mm wide
• Black Floyd 26 x 3.8˝—Best used with rims 50 – 65mm wide
• Fat tires (3.7 – 4.3˝) —Best used with rims 50 – 80mm wide
• Fatter tires (4.5 – 4.8˝) —Best used with rims 65 – 100mm wide
The other big problem with making your own 2WD fatbike is the drop-out widths are not standardized. Double check front and rear drop-out width before purchasing a frame. As an example, one of the cheapest Fat frames right now is the Walmart single-speed Beast, and their 7-speed Dolomite. I have been told that a rear hubmotor can be laced to the fork (I haven’t tried this yet, so exercise caution), and the rear drop-outs have a 190mm width…too wide for any stock rear hubmotor axle. I have heard of retailers that will build a hub with a longer axle, but of course it will cost extra and there is a significant wait time.
Also be aware, if the axle is not very strong, the added length can make a bent axle more likely, so run low air pressure to absorb bumps, and don’t hit any curbs on purpose if you can avoid it. I will post more info on a DIY 2WD fatbike as it comes in from builders…
(edit) 2WD fatbike kits!
Just a month after this article was published, I found several sources for 2WD fatbike parts. One of our top-rated vendors, em3ev.com, has already had a lot of their customers place a 135mm drop-out width stock REAR hubmotors from MAC in the front forks of a fatbike. Now…Paul is stocking rear MAC hubs with a drop-out width of 175mm (in the popular 10T and 12T windings) to allow them to be used on the rear of a fatbike (depending on which fatbike model you have). Its not in the web-catalog yet, but they do have them. Make sure to tell them you read about it here!
HEH (shown above) makes and sells complete 2WD E-fatbikes, and NOW…they are making their fatbike bits available as a kit (for fatbike owners who already have the bike, and it is the a model that will accept their type). They have verified (so far) that the Motobecane FB4 Phantom and a Surly Moonlander have the asymmetric rear chain-stays and drop-outs that will fit their kit.
Surface604 makes and sells fatbikes + E-fatbikes, and they NOW also sell the REAR 36V geared hubmotor that they use on their electric models. This is a great development, because as I have stated before, the front fork will accept the stock axle from rear hubmotors (if both have 135mm drop-outs).
Thanks to ES member Ch00paKabrA, who sent me a link showing that now…Bafang is making and selling their smaller 350W geared hubmotor with long axles for 190mm drop-outs (for the rear of a fatbike). These motors are a little small for a single-motor fatbike, but if you use TWO of them for a 2WD, they would likely be adequate, plus their modest size would be fairly stealthy. Again, the stock rear 135mm drop-out hubmotors would “probably” fit the front forks of most fatbike frames with no modifications.
Kinaye Motorsports is now selling the hot rod MXUS 3000W rear hubmotor with an extra-long axle for the rear of a fatbike.
What would I get right now?
I haven’t done this yet, so I don’t know what problems would come up, but…I’d get an affordable Mongoose Dolomite 7-speed, put a long-axle rear MAC from em3ev.com onto the backend. I’d get one of their triangle battery packs that was capable of safely putting out 40A (made from the very safe “non-LiPo” 18650 cells found in cordless tools), and later, I’d put a rear Bafang-BPM onto the front (with torque-arms all around). The cost would be around $1600, and you would have 50V X 40A = 2,000W driving a 2WD fat tire bike.
Later, I’d top it off with a Thudbuster seat-post (or maybe a Suntour NCX?), so…between the fat low-pressure tires and the Thudbuster…it would ride like a dream floating on a cloud…without the weight or expense of full-suspension components. It would be the affordable AWD Jeep of the E-bike world.
Written by Ron/Spinningmagnets, January 2015