Tinkering with e-bikes

In terms of balancing convenience with healthy lifestyles and environmentally conscious modes of mobility, e-bikes are at the top of many lists. Here is a good account of the benefits of e-bikes in Slate.  The main problem for consumers is that most quality e-bikes are $2000 or more and often in the $3500-4000 price range. The alternative is to use an e-bike kit consisting of a motor unit and a battery and modify a bike into an e-bike. Extremely cheap e-bikes in the $800-1100 range should be avoided. This post outlines the process I went through in building an e-bike. It is a series of reflections on the key moments in the process of deciding on the elements of the project and then an evaluation of its success.

There was a specific goal for the build, but this existed in a much broader range of reasons for the project. The specific goal was to encourage my non-cycling wife to commute by bike. The other major reason, but which is more contextual and formless in scope, was that I also wanted to her to experience Canberra from the saddle. Canberra is a great cycling city and even through commuting on cycle paths alongside major arterial roads it is possible to see a side of the city that is otherwise hidden. Suburban and urban Canberra is framed by bush land and waterways that give a texture to cycle commuting that can be repeated in different ways in most other major cities.

e-Bike Design

There are a series of decisions about the design of e-bike as there are different ways of adding an electric motor to the cycling system. There are basically two major designs for electric motor location, either hub-based (‘in’ the wheel) or mid-mount (replaces the crank). Similarly there two major locations for the battery, either integrated into or alongside one of the major structural elements of the frame (normally the downtube, the part of the frame from the head tube — what the fork and handlerbars are attached to — to the bottom bracket — what the crank is mounted) or sitting on a rear rack. The cheapest systems replace a wheel with a hub-mounted motor and locate the batter in a rear rack. All high-quality factory e-bikes replace the bottom bracket with a mid-mount design and locate the battery in or mounted to the downtube. The other major design decision is whether you want a pedelec system, which is torque-activated by pushing down on the pedal, or cadence or speed operated, which is activated by motion by the cranks or the wheels.

After a process of researching many different combinations I chose the Tongsheng TDSZ2 mid-mount motor and a downtube-mounted battery. Endless Sphere is a very useful resource for researching previous builds and other people’s experience with different combinations. This is a good thread on the TDSZ2. It is currently the only mid-mount motor that has torque activated assist. A year ago there was only a 250-350w version, but now there are 500w and 750w versions. This was purchased via Ali Express. The major alternative to the Tongsheng TDSZ2 is the Bafang mid-mount series. The Bafang kits have a very strong following amongst those who want extremely high powered applications (1kw+). Bafang make a torque-activated system but it is designed for special frames. The TDSZ2 can be fitted to and replaces the crank in pretty much any modern bike. In Australia, e-bikes need to be 250w max to be legal.

The battery decision was slightly easier as the commute was 25-28km in total (12.5 to 14km each way depending on the exact route), there was not any need for a very large battery. I chose a smallish battery of 10ah that came with a charger, purchased from eBay. At the highest assist level with my riding and my daughter’s trailer attached, this provides about 45km of range.

Lastly, I took advantage of a “20% off” e-Bay code to buy a new Reid Urban X3. The Reid Urban range is basically a hardtail and rigid (ie no-suspension) mountain bike setup as a flatbar road bike. It is far from the lightest bike, but it is designed to be more robust than lightweight road bikes. They seem to be out of stock of this model. I ordered ‘large’ size to suit Anne’s height. The basic requirements for a base bike for this build were:

1. At least a 10 speed gear system. The Urban X3 comes with a Shimano Deore rear derailleur and cassette.
2. Hydraulic disc brakes for improved braking. it could handle the power of the electric system.
3. Robust design. Basically a heavy duty frame, probably based on a mountain bike or a commuter bike. A current alternative for those doing cycle path or road-based commuting could be a ‘gravel’ bike.

Assembly

 

As well as the parts that came with the motor kit, battery and bike, I needed a suitable plug to connect the motor kit to the battery and I purchased some black heatshrink to cover-up the cabling from the battery to the motor. During the build I discovered the 11 speed quick links I already owned would not work, so I also bought some 10 speed quick links. I built and tuned the bike with an old 11 speed chain on it.

The mechanical work was relatively straightforward. Removing the factory crank was straightforward (there are youtube videos to assist this step if need be, like this) and the TDSZ2 comes with instructions for installation (here is a good youtube video). The battery mount bolts to the downtube. The two most time consuming aspects of the build involved, first, cutting down the wiring and fitting the plug between battery and motor, and, second, cutting down the left-hand grip (with a hacksaw) to fit the XH18 display (seen below, the ‘grip’ part adjusts the level of assist or in the menu mode can select different options).

I already have a pretty comprehensive set of home bike mechanic tools from building my other bike. A bike stand is extremely handy as is a set of specialist bike tools. Aldi had both as ‘special buys’ in late 2016 and they have been invaluable ever since.

Budget

• $600 for bike with 20% off code (normally $749)
• $400 for motor kit with Ali Express vouchers (normally $420, now it seems it is $450)
• $349 for battery.
• $15 total for plug, quick link for a 10 speed, and heatshrink.
• Additional but not necessary: Toolkit was around $50 and stand was I think $60, but I already owned these.

Total around $1365.

Use and Further Design Changes

The e-bike project was extremely successful in its primary goal of providing the basis through which my wife could explore or not cycling as a commuting mode. Anne has since changed employment and I instead use the e-bike with further modifications to tow our daughter in a bike trailer.

These further modifications include:

1. The Urban X3 seat was actually terrible and has since been replaced with a Specialised Body Comfort Gel.
2. I broke a spoke in the rear wheel after two weeks riding it 3 or 4 times per week and did not trust the wheelset to handle my bulk. The wheelset has been replaced with a set of 40 spoke 29er wheels.
3. Shimano e6000 175mm cranks. I have longer legs and the motor kit’s cranks are only 170mm.
4. 46T mainring. Kit comes with a 42T. I can sit on much higher speeds when on the flat.
5. I fitted a longer stem (110mm over 100mm) that I had laying around and have also ordered wider riser handle bars. These would likely not have been necessary if it was an extra large size frame origainally.