Tag Archives: Bafang

Pedal-Assist for my Surly Disc Trucker

Tongsheng TSDZ2 Mid-Drive
Tongsheng TSDZ2 Mid-Drive

Start of a New Year and another year older!

Last year’s (2020) “Covid-style adventures” where I limited myself to short bicycle tours to the local Southern Gulf Islands of British Columbia made me realise that I am getting older and those “bloody hills” on the islands are getting tougher year by year, especially when fully equipped with a touring/camping load on the bike! I also noticed that year by year, more stops on the longer hills were required to catch my breath and to bring my heart rate down from the stratosphere! So with a little research I discovered that I’m not the only septuagenarian cycle-tourist that may need a little boost up those “bloody hills!”

With a limited budget and without the will to add yet another bike to my stable (which I have worked diligently to reduce already), a full on e-bike was not in the cards. Besides, for a touring e-bike there is little choice in North America. Most of the available e-bikes are more designed on the “comfort” bike style of design for the casual rider or commuter. The other factor was that I wanted a pedal-assist e-bike that actually required me to pedal and use mostly my “horsepower” and not just sit there and let the battery and motor do all the work. At least I could feel that I was cycling, even though I would be transgressing somewhat to the “dark side!” Many a younger cyclist may scoff and call anyone riding an e-bike a “cheater,” but in fact the pedal assist e-bikes still involve a fair workout especially when used at the “eco” or low power assist setting.
Moreover, if and when some longer bike touring would be safe to achieve, or some credit card touring possibilities without my camping gear load, I may want to remove the pedal assist motor parts returning the bike to it’s “normal” mode and ride without the worry of battery life creating “range anxiety.” In addition, I wanted a kit that would require as little change to the bike’s components as possible.
After installing the TSDZ2 I knew that I could confidently return the bike back to normal in a couple of hours, so not a big hardship.

TSDZ2 Kit Components
TSDZ2 Kit Components

I researched – ad nauseum – a few do-it-yourself kits to add to my Surly Disc Trucker touring bike and ended up choosing a Tongsheng TSDZ2 mid-drive kit. I did research front and rear hub drive kits but they basically only have a pedal assist system that is mostly determined by cadence sensors and often let the motor do most of the work, so not the standard that I desired. A mid-drive kit seemed like the best proposition and much liked by many riders/reviewers on the internet. That left me with a choice of the Bafang BBS series mid-drives or the Tong Sheng TSDZ2 mid-drive that I eventually chose. After serious mulling, the absolute main reason for my choice was that the TSDZ2 utilises a torque-sensor for the pedal assist. Essentially that means that the drive responds to how much pressure it senses on the cranks. So no pedal pressure from me, results in no help from the motor! With the TSDZ2, one has to pedal to activate the pedal assist. There are four levels of assist, Eco, Tour, Speed and Turbo; the range of the battery is directly linked to which level of assist one chooses to ride with; hence judicious selection of assist levels will determine the distance possible on one charge of the battery. Other factors that may limit battery range are the rider’s weight, load carried, gearing and terrain etc.
E-bike batteries come in different voltages, shapes and sizes, so once again, the larger the battery, or wattage, the greater the distance that can be ridden. Notwithstanding the above, the TSDZ2 kit does ship with a spring-return throttle. I wasn’t really interested in this function, but after a little more research, I learned that the throttle could be very useful for a hill-start. If any of you readers has experienced trying to get momentum for a steep hill-start with a loaded touring bike, you will appreciate that sometimes it is not an easy task that can result in a bit of wobbling etc., not fun with traffic speeding by!
The drive weighs about 6 pounds and the 12 amp/hr battery about 7 pounds, so obviously, adding an e-drive to a bike will add to the overall weight, but it is a trade-off to achieve some pedal assistance!

The TSDZ2 kit fits 95% of standard bike frames with 68-73mm bottom bracket and can be purchased in a few “flavours,” namely various motor voltages and wattages and even with varied displays. The most common kit that I found usually offered a VLCD5 display, which is one of the larger displays available. The kit that I ordered is a 48 volt, 500 watt kit with a 48 volt, 12 Amp/hr battery. There are larger and smaller batteries available, but for more range I would probably rather have a second spare battery than one larger one. For now though, just the one battery to install.

Onto the install…

11-42 8 Speed Cassette

I mentioned battery range above being tied to various variables including gearing, low gears will place a lower demand on the battery just as low gearing requires less effort when cycling without pedal assist. My present cassette gearing was for a triple chainring setup which would have to be removed thereby losing my 20T granny ring.

DR Hanger Extension

As a close alternative, a larger low gear cog on the rear cassette would be in order. I managed to scope out an 8 speed 11-42 cassette, but even my long cage derailleur would not shift into the 42T cog, so this required the installation of a derailleur hanger extension.
That easy fix worked out well with no other changes to the rear derailleur setup and it shifted fine with my present thumb shifter.

Next step was to remove my crank and bottom bracket then install the mid-drive unit into the bottom bracket shell. I tried to insert it but it stopped halfway through. Removing it showed the problem; the screw holding my derailleur cable guide was too long and poking through into the space. I shortened a screw to fit and looking through saw no obstruction then installed the drive with no further issues. I wanted to keep my front derailleur cable in place, as I figured that I would add one more chainring to the single ring that the drive came with to enhance the gearing range. So I was glad that there was just enough space for my cables and that I didn’t have to reroute them.


The challenge at this point was routing my front shifter cable from the bottom bracket guide up to the derailleur! The drive installation comes with a mounting bracket that basically acts as an anti-torque arm to prevent the drive from moving radially. The issue was the the top plate of the mount interfered with the route of my cable. To address this issue, I drilled a small hole in the top plate to run the cable through. This worked somewhat fine but I was still not 100% satisfied with the result.

During my browsing for an e-bike kit, I did notice that the anti-torque mount/bracket would not work on some recumbent bikes with no chainstays to hold the top plate, and as an alternative used a boom clamp system. I adapted this method to fabricate a similar clamp to fit around just one of my chainstays. I fabricated my clamp from 16ga (approx. 1/16″) stainless steel and it does the job admirably! And no inference for the front derailleur cable with this method.

Drive Mounted in Bottom Bracket

Once that clamp was in place, I finished tightening all the drive to bottom bracket bolts and the large 33.5mm locknut with the supplied wrench.


Before I could run the cables, I had to decide where I would mount the battery. The most popular location is inside the main triangle of the frame utilising one of the locations of the water bottle mounts. I didn’t want to lose any of my water bottle mounts which led me mount the battery on top of the rear rack. I had to lengthen the two battery wires from the motor to allow this rear location. I didn’t like the standard bullet connectors that the drive’s battery connections shipped with, so after soldering on some longer wires, I added a superior XT60 connector for the main power connection. I added shrink tubing to all the new wiring as added protection from the elements. At the same time for weather protection, I brushed liquid tape over the motor’s wiring where it exited the drive.

While I installing the battery mount and wiring I noticed that there wasn’t a cable clamp where the wire exited the battery mount. I disassembled the mount and added a small cable clamp and shrink tubing to the wires. I also ran the rest of wiring up to the front of the bike for the control display and to the speed sensor at the rear.

My butterfly handlebar had limited space for the display and throttle to be mounted; luckily I had an old handlebar bag bracket that I used on a previous bike that I could mount facing towards the rear of the bike to accommodate the large display. That bracket installs onto the 1 1/8″ steerer tube and fitted the display perfectly.

Even with a 42T cog on the cassette and the stock 42T chainring, I didn’t feel that was low enough gearing for the motor to cope easily with a loaded touring rig. The outer chain guide of the TSDZ2 crank could be removed to add another 110mm 5 bolt chainring, which I ended up buying as a pair due to that option being more economical; the pair were 34T and 42T rings. I mounted the 34T on the inside position and the stock 42T as the outer ring. But my front derailleur would not swing out far enough to reach the outer 42T ring. Fortunately, the 42T ring that I purchased with the 34T had only a slight dish to it (unlike the deeper dish of the stock chainring), so I installed that with the dish pointing inwards. And although the spacing between the rings was minimal, it worked a treat with my derailleur! As I had a triple thumb shifter, I locked out the number one granny position with a longer limit screw to prevent the chain derailing off the inner 34T ring.

While I was messing around with the chainring business, I installed the stock crank arms that came with the kit, they fit ok, but my Q-factor had increased substantially and was offset mostly to the right-hand drive side of the frame. Q-factor is the distance between the outside of one crank arm to the outside of the opposite crank arm, also referred to as “stance width.” I noticed that the stock crank arms had quite a rise/bend to them thereby increasing the Q-factor. After some browsing on the ‘net I found information that would solve this issue somewhat, by installing a straighter Bafang crank arm (which was a lower rise by about 15mm) onto the drive side of the bike and leaving the stock crank arm on the left. The Bafang crank arms are widely available at an inexpensive cost.

The different angles/bends of the crank arms can be clearly seen on the above photos.
My original Q-factor prior to the install of the motor drive was 185mm – with both Tongsheng crank arms it increased to 210mm – the final Q-factor with the Bafang crank on the right is now at an acceptable 192mm. The crank arms are also somewhat more equidistant from the centre of the bike with only a 10mm offset. I could have also installed a Bafang crank arm on the left to reduce the Q-factor even more, but that would have decreased the distance from centre to the left crank arm and perhaps felt strange to ride.

Well, that was about the end of the install process, so after setting up the wheel diameter in the display configuration, I took the bike for a short run around the block. Everything worked very well and I could feel the torque sensor kicking in to assist as I pedalled harder, also both front and rear gear shifting was as it should be. What I didn’t really like was the overly large display, so back on the ‘net! I bought a VLCD6 display which with an adapter cable is a straight swap for the VLCD5. The VLCD6 is a much more compact display with nearly all the features of the much larger VLCD5. In fact, the only difference beyond the size is the lack of being able to install the electric brake system, which basically stops the motor when the brake lever is depressed. With the TSDZ2 this is not really necessary, as once one stops pedalling (braking procedure!), there is no more response from the motor.

I did have to move my original odometer forward a bit and mount a short handlebar extender for the display and throttle, but both are easily in reach now. The large display and custom mount that I installed originally are gone, leaving a much more compact setup.
All in all, I only removed the cranks, bottom bracket and cassette from the bike, everything else is as it was, which was my intention to be able to switch back to “normal mode” easily and not ending up with a “Frankenbike!”

Surly - E-drive Kit Installed

I measured the ground clearance to the bottom of the drive to be an adequate 7″. No log or kerb jumping with a touring bike anyway 😉

During this build, I gained a large amount of knowledge regarding e-bike motors, battery technology etc. from various sources on the Internet, which made this a very interesting and rewarding project.
In conclusion, I still have to really test out the bike with the pedal assist kit during a good ride both unloaded, and then with my touring load (on some “bloody hills”) to determine battery life and any glitches etc. I’ll post another report on this blog after the trial runs – which may be a while as the weather here in BC is very wet right now with one rain squall after another! When a decent day or two appear, I’ll be out there!