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 stock 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!

11 thoughts on “Pedal-Assist for my Surly Disc Trucker

  1. Raymond Verlage

    Hello, Adam:
    I was contemplating disposing of my large frame 90’s Brodie Torque for an e-bike. Your post and others inspired me to keep and convert it to electric with a more upright seating position. It has Deore XT derailleurs, with 44T as largest front. The bike would be used mostly for pleasure trails around the Okanagan. It currently has V brakes. I’m 6’2″, 190 lbs.
    – Do you still recommend the TSDZ2 unit?
    – Does yours have the OS upgrade to 48 or 52 V? I was planning to go that route.
    – What battery would you recommend now?


    1. AdamK's Cycling & Travel Post author

      Hi Raymond:
      If you are happy with your bike then an e-kit would be a good way to go. Disc brakes are recommended for full-on e-bikes but the TSDZ2 is torque sensing so when you stop pedalling there is no assist, your v-brakes would probably be ok.
      I bought a standard 48V 500w unit without the OS upgrade and it works fine for my needs as you can read from my blog posts, and yes I do still recommend it after riding with it for the several months.
      I do recommend a smart charger for battery life as I’ve mentioned also.
      The best (long life, and lasting charge) batteries have either Samsung or Panasonic cells. Sometimes you will see a 13ah battery cheaper than a 12ah, but the 12ah probably has Samsung cells! I bought 12ah batteries, which are fine for my needs and I can get all the range that I need for now without a heavier battery such as a 17ah or even higher ah.
      You won’t need the front derailleur (unless you are touring with a load), but a low geared rear cassette would be good as, just as your legs, the drive works easier when you shift to lower gears.
      The TSDZ2 comes with a 42T chainwheel, but others are available. I wouldn’t recommend a higher tooth count, but lower is good if loads are anticipated. As you can read from my conversion, it is possible to finagle a dual chainring on the front, but it does require a little cobbling!


  2. Dan

    I’ve followed your site for several years. I appreciate the thoroughness of this write up and hope that you will update after you’ve spent more time on the Esurly.


    1. AdamK's Cycling & Travel Post author

      Hi Dan, yes I will be adding a post regarding my test runs of the “Surl-e” with the pedal assist. I’ve already ridden a couple of runs including one loaded or overloaded actually! I’m recording some basic stats and when the weather improves I’ve got the bike ready for another loaded run.


  3. John InParkHill

    Really interesting read, Adam! Thanks for the detailed step-by-step. I’m just getting into touring at a (somewhat) younger age (mid-50s) but may be interested in adding something like this if my body doesn’t want to keep touring as I age. I planned a 1500 mile tour last summer and cancelled it due to Covid. I have something similar planned this summer assuming things are improved. All will be unassisted, but I do wonder what a conversion would cost if I decided to go that route.

    May I ask what the final price-tag for your upgrade was? Doesn’t have to be exact – ballpark is fine.




    1. AdamK's Cycling & Travel Post author

      Hi John, cost for the whole basic kit including the 12 A/H battery was about CAN$900 + CAN$100 for shipping. Shipping costs are high due mostly due to the restrictions and requirements involving the shipping of large Lithium batteries. This was from Amazon, but the supplier that they use is a Chinese company (I think?) called Greenenergia – they are great to deal with and answer any queries or changes very promptly in plain and very fluent English. They also provide accurate tracking info too. I changed from the manual brake levers shut-offs to the small switches for my hydraulic brakes with no problems – as it was I didn’t install them anyway! Later, extra costs involved were for the smaller VLCD6 display and the chainrings, but that was just my preference. I got those from Aliexpress.


  4. Ron Richings

    Excellent write up Adam. May be looking at something similar for my RANS V2 recumbent. Not sure if mid drive is possible with the unusual bottom bracket/frame tube configuration of that bike.


  5. Mark Boyd

    My bikes – upright and recumbent – both use the 36 V 250 -350 watt motor setup and the lighter 36v 10.4AH battery mounted as low as possible. I found the extra mass changed the moment of inertia enough that I really had to readjust my approach to fast riding on twisty road on my unloaded upright bike a a lot. I can no longer simply toss it and catch it like I could without that extra mass hung on the frame. This, of course, was never an issue while doing loaded touring, but now, because of the pandemic, I’m only doing unloaded riding.

    I initially mounted the throttle on my upright bike, but found that I didn’t use it. there is a boost fact built in to the torque sensing when you start pedaling which really helps getting started on steep hills. I do have the throttle mounted om my recumbent and, have needed it for getting started when I have stopped on a steep hill in too high a gear.

    I have 34/46 110 mm BCD front rings with 12/36 9 speed cogs on my upright bike and 104mm BCD 32/44 rings with 11/34 cogs on my recumbent. I bought a 104 mm BCD adapter so I could put slightly smaller rings on my recumbent because of chainline issues.With the stock 42 front ring I was able to climb sustained 20% grades on my unloaded upright but having a 34 ring is better for my normal, quite hilly, riding.

    Unloaded, on either bike, I can do about 60 miles with a mile of vertical on one battery charge riding in ECO mode most of the time.

    Liked by 1 person

    1. AdamK's Cycling & Travel Post author

      I opted for the 48V setup in order to try and accomplish a little more range, perhaps? Battery weights between mine and yours amount to about 1 to 1 1/2 pound difference, so not really a deal breaker for me. If I had gone for the larger Amp/Hour batteries, then yes the poundage adds up. Regardless the end result is good. I rode 54kms on a trial run, unloaded and as this is my touring bike, which normally I never ride unloaded, I still didn’t see an issue with the battery mounted on top of the rear rack as far as handling and the battery still had lots of life left in it. On another short run (8km) with all my touring/camping loaded, the bike felt heavy at first, but once I started off it was really nice having the drive just on Eco mode to help the legs. I rode a couple of short steep hills too and even in Eco mode with my low gearing, it felt as if I was getting a decent amount of help. So yes, having the 34 ring is an definite advantage, and especially so with that large 42 cog at the rear. Mostly though I can stay in the 42 chainring; I’m going to try a 44 ring when it arrives. I’m waiting for some better weather then I’ll load the bike up again and see what kind of range I can accomplish – I’d just like to have a better idea of range before I set off on a trip proper. I’ll add another post with some more information when I have ridden the bike more.

      Liked by 1 person


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