bikesnobyyc fat bike - OpenSourceEBike/TSDZ2_wiki GitHub Wiki
A fat bike conversion with a TSDZ2 is entirely possible, but there are a few important considerations that need to be addressed. The discussion below relates to a conversion I did in 2020 on my 907 aluminum fat bike (2013 model) with 4.8” tires.
- First, I would recommend a 48V motor and 52V battery for this purpose. A fat bike will spend more time at lower RPM and will require more power and create greater loads when riding winter trails; by using a 48/52V setup, you can maximize power and minimize heat. Consider having a temperature sensor installed if you’re really worried about heat, but I just set mine up for 15A maximum battery draw and it hasn’t posed any problems – besides, I want the throttle (see below). I see short peaks of 700W+ on steep terrain, but for the most part my motor is running at 300-400W.
- You’ll need a fat bike extension and longer crank spindle to fit your bottom bracket (fat bike BBs are typically 100-120mm wide). You can find these online from a number of sellers, but you’ll need to tap threads into the motor’s spindle housing to thread the adapter onto the TSDZ2. Tapping these threads presents a problem without the necessary tools and an alignment jig. If you’re buying a new motor, I would highly recommend buying it from EcoCycles with their extension kit (https://www.eco-ebike.com/collections/tsdz2-accessories-parts/products/tsdz2-upgrade-bottom-bracket-axle-extension-in-92mm-100mm-120mm) – they will tap the threads for you and install the extension, saving you a lot of time and hassle. Their kit works perfectly and comes with all the hardware for fitting the TSDZ2 onto a fat bike.
- When installing the motor, have a few of BB spacers available to optimize the chainline. Metal ones are better than plastic as the plastic ones can deform if they’re right up against the BB shell on the frame.
- I highly recommend a 30T offset chainring for a fat bike (see picture). The gearing is much better suited and the chainring is offset slightly inward to improve the chainline. You can find these online.
- I highly recommend the metal gear to replace the blue plastic gear. Your fat bike will see more load than a normal street bike if you ride it in the conditions it’s meant for.
- I also highly recommend a straight right crank arm to reduce the Q-factor of the cranks (the width between the pedals). The standard TSDZ2 crank arms result in the pedals being much too far apart. On my build, I invested in some custom crank arms from Lekkie (https://lekkie.bike/product/buzz-bars-left-offset-170mm-v2-1/), although you can also just use a Bafang straight right crank arm for much less money.
- This point is really important. You need to custom fabricate a plate to hold the motor in place and keep it from rotating forward around the BB spindle axis. The stock plate the TSDZ2 comes with is simply too small to fit a fat bike. I used some stock aluminum material from a hardware store and doubled it up for strength, which has worked really well (see pictures). I wanted to avoid steel to avoid rust. There was a bit of trial and error to get this working properly – when I used only a single aluminum plate, the motor had enough torque to bend the plate and suck it through the chainstays. Before that I just tried to bolt the factory plate to the right chainstay and it was also pulled through (and dented my frame where the motor slammed against the downtube). To get everything to hold, you’ll also need longer bolts and spacers to center the bracket in the middle of the chainstays and compensate for the extra thickness – I used metric bolts and oversized nuts as spacers that I found from a hardware store (see close-up pictures).
- I installed a left thumb throttle in place of the left shifter that was removed. The throttle is invaluable on a fat bike in snow as it makes it much easier to get going again when you’ve stopped. For this reason I skipped the temperature sensor.
- Finally, I changed my cassette on this build to a 10-speed 11-42T (SunRace). The bike started out as a 2x10 setup with an 11-36T cassette and 36/22T chainrings, but I lost some low-end gearing when I switched to the 30T single chainring. If you have a newer bike, this might not be an issue at all, but this bike is a 2013 model with Shimano XT parts from that year. I would say the gearing is now perfect and the bike can climb even the steepest snow-covered trails. Converting an older 10-speed to such a wide cassette can cause problems with reaching the large cog, and I used a longer B-screw for the derailleur to make it work. Another option is to buy a new rear derailleur to handle the extra teeth, or use a GoatLink (https://www.wolftoothcomponents.com/products/goatlink) to improve your existing derailleur capacity. This can be a bit hit and miss, but it should work. Make sure to keep enough chain in contact with the smaller cogs to avoid slippage under load.
There you have it – a custom TSDZ2 fat bike that can handle anything you throw at it. I regularly ride this bike on winter trails in the mountains west of Calgary and it has performed extremely well. There were some minor teething problems at the start just keeping the motor from coming loose and moving around, but the custom bracket now keeps it all in place and I’ve had no further issues. The bike can handle the steepest terrain one would think of riding, and the top speed is still around 34kmh with the 30T chainring and 11T rear cog. I hope you find my experiences useful for your own fat bike conversion.
