After making 4 different electric fatbike prototypes out of Bikes Direct aluminum fatbikes I’ve decided to try a different route entirely. The new Storm fatbike is selling their entire fatbike with battery, charger and motor for a measly $499 (till this Friday 2/6/2015). Considering that I usually drop more than that on a motor or battery alone this is a screaming deal that just can’t be ignored. The last time I went shopping for decent 4.9 inch tires they ran about $130 each shipped, and for rims that wide the cheapest I can find is $50 each and those are for heavy double wall rims without holes. The biggest pain when building an AWD fatbike is lacing the front wheel to a motor. The Storm comes with a motor already laced and mounted with it’s own battery, the problem is that it’s on the wrong wheel.
Since the frame is steel that means we can bend the front forks with relative impunity. So in a few easy steps we have a super cheap singletrack/deep snow machine.
1) Pull off the back wheel and remove the freewheel.
2) Mount it on the front by stretching the front forks so the dropouts fit with the bigger axle.
3) Buy a cheap rear hub/freewheel on ebay with similar hub spacing and re-lace the front wheel on the new hub (or have your bike shop do it for about $40). Instructions on lacing wheels can be found here.
4) Mount a single speed freewheel on the axle, get the biggest one you can find, I recommend a 22T at the very smallest. Mount the old front tire now relaced to a new axle to the rear dropouts.
5) Grind off the bottom bracket to mount a stock BBS02 750 mid0drive unit on the crank. I recommend getting a cheap BCD104 adapter and throwing on a 32T chainwheel on the front. If you don’t want to grind the BB you can always use the 100mm axle conversion kit from California E-bike. I can’t get any decent pictures of the BB but it LOOKS like it can be easily ground down to 68mm or so without hitting the chainstays.
6) Put a beefy BMX chain on it and some tirechains if you want to hit the really deep powder.
7) If you don’t have a 48V pack that will put out 25Amps then you will have to build a 12S2P pack. The cheapest way to do this is with Zippy Flightmax packs found here. Lipos are no joke and you can easily hurt yourself or burn down your house, so spend some time asking questions about how to not kill yourself on endless-sphere first. If you are accident proned or tend to hook things up wrong you might be safer with Lifepo4 batteries.
8) Get rid of that stupid looking kickstand.
That’s it, you are done. With the street price of the BBS02 at around $500 (we recommend that you buy from Paul at em3ev.com) that means you have built an awesome singletrack bike that should be able to plow through 6-8″of powder with chains, puts out about 1400 watts and should be good for several hours of riding. I would stack the thumb throttles so they overlap such that when you push the throttle for the BBS02 the front wheel ALWAYS activates, but if you press the Front wheel throttle that it can work on it’s own. The idea is that if you want to go over about 8-9 mph the BBS02 is going to be maxed out because the drivetrain is set so low from the gearing on the crank and freehub. On the road or beach you’ll just want to use the front motor only, it will be much more efficient at higher speeds and should be able to do somewhere close to 20 mph, although I suspect the top speed will be closer to around 17mph.
For weight figure 7 lbs for the Zippies and about 9 lbs extra for the BBS02 which should put the total weight in at around 60 lbs for the bike if the Storm really does weigh in at 45lbs. Figure you can save a pound or two by swapping out the seat and the tubes with lightweight ones. I suspect for my bike I will upgrade the brakes to BB7’s which you can get about $50 for a pair on ebay shipped from Hong Kong. I also plan to upgrade that ridiculous seat and the overweight tubes. I’ve been running the Q-tubes in 4.9 inch tires with 80mm rims with no issues and that will almost certainly save a pound or three.
Update: Paul is now selling a FatMAC motor which will fit in dropouts that are 170-185mm. Since you have to relace the front wheel anyway it might make sense to use a FatMAC 12T motor instead of the BBS02. It won’t have quite as much torque, but it will max out at 15mph instead of 10. It is also a lot cheaper at around $270 for the bare hubmotor (no controller or throttle). By the time you add spokes, a controller and throttle you’re going to be in the $400 range (before shipping). The Upgraded MAC 12T is the only hub motor that I recommend for single track as most other hub motors I’ve tried are too wimpy or way too heavy. To find the right spoke size you’ll have to look on his website here and use the spoke calculator once you measure the ID of the Storm’s rim as accurately as you can. Buy 2-3 extra spokes as they are a pain to find the right size when they break.
You can buy a Storm now through this link.