Riding the Volts: Converting my MTB to Electric
I have a theory, or rather, let’s call it a theory of minified huge experiences. It’s all about scaling down those grand adventures in life. Take, for example, the exhilaration of driving an F1 car, feeling the raw power of torque and speed. According to my theory, that experience can be scaled down to the thrill one feels while accelerating downhill on a bicycle (with brakes that can barely stop you). But here’s the catch: I don’t own an F1 car, and not every road is downhill (motivational speaker ehhhh ?). That’s where electromagnetism comes in — I decided to electrify my bike.
For this project, I used my 2016 bought Btwin Rockrider 500 . It’s an entry level MTB with full aluminum body weighing just 13 kgs (it has remained same although I have not) and with 24 gears to power through.
Sizing the electric powertrain system for the bike was easy thanks to my job as it requires me to do same for Electric Trucks. With all that experience I started figuring out the motor power I need and how much battery size would be enough for my needs.
When it comes to converting an ordinary bike into an Ebike, there is one significant design choice: what type of motor to choose: A mid-drive motor or a hub motor. While the mid-drive motor offers better performance, it can be quite a hassle to install. So, I opted for the hub motor. It fits snugly into the rear wheel, making the installation process seem simple (or so I thought).
There are the two key factors that define an electric bike’s performance: torque and speed. In its simplest form, higher voltage leads to higher speed, while higher current results in more torque, that exhilarating acceleration. With that in mind, I started exploring vendors on Indiamart and eventually settled with Geekay. They provided me with all components that almost matched my desired specifications (I had my eyes set on a 48V system for that extra speed, but alas, it wasn’t available).
Let’s take a closer look at the components:
· 36 Volt 250 Watt BLDC Hub Motor: Enough to propel me up to a delightful 25 km/h.
· 36 Volt 10Ah Lithium-ion Battery: With an estimated energy consumption of around 12 watt-hours per kilometer, this battery grants me a range of 25–30 km.
· 36 Volt 12 Amps Controller
· 36 Volt and 2 amps Charger
· Throttle: For controlling the e-bike motor, just like twisting the throttle on a regular petrol-powered bike for that extra burst of speed.
· Pedal Assist Sensor: This clever sensor counts the number of pedal rotations and signals the motor to provide assistance, making pedaling a breeze.
After a four-day wait, the components finally arrived, and I dove headfirst into the installation process. However, the real challenge began when I attempted to install the hub motor — an experience that humbled me. I had naively believed I could handle it on my own, but it turned out to be more complex than anticipated. Here’s why:
The bike I own wasn’t designed in India, presenting some unique challenges in conversion:
1. Spokes and Rim Size: I had ordered spokes for a standard 26-inch wheel, but due to the tire wall size on my bike, they didn’t fit properly. Additionally, while most bikes have 32 spokes, mine had 36. Consequently, I had to abandon my old rim and invest in a new one.
2. Freewheel: Unlike a detachable freewheel, my bike had an integrated one with a gear cassette, which required me to purchase a downgraded freewheel. As a result, I now have 21 gears instead of the original 24.
3. Bottom Bracket: The original bottom bracket didn’t provide enough space to install the pedal assist sensor. Thankfully, the vendor agreed to send me a larger bottom bracket, allowing me to fit the sensor successfully.
These were the major obstacles I encountered, which taught me that in the world of e-bikes, there’s no problem that can’t be solved by investing a little more money and seeking the expertise of a good mechanic.
Despite a few minor hiccups along the way, I managed to get my bike up and running within a day. The installation process was backbreaking, but as soon as I twisted the throttle and felt the bike accelerate, all the pain seemed to vanish (well, not all of it — I did hurt my fingers and my ego a bit).
With my newly converted electric MTB, I reached a top speed of 29 km/h just using the motor. When I added my own pedaling effort, a speed of 35 km/h was comfortably achievable. The battery also lasts about 25 kms when using pure motor power. In the assist mode it depends on how much work I am doing and hence am yet to find a number on range but surely it would be higher than 25 kms. The battery takes four and half hours to recharge. Considering 360 Wh of battery lasting 25 kms per charge, my running cost comes to be (360/1000Wh)*(7Rs/kWh)/(25kms)= 10 paise per km (Good price to pay for the fun).
Now, let’s talk money. The entire conversion cost me around Rs 21,000. This includes the electric drivetrain components, labor charges for fitting the hub motor, and the new bike components (rim and freewheel). I know what you might be thinking — why not simply buy a new e-bike for around Rs 30,000–35,000? Well, my answer is simple: “Fun.” There’s a sense of satisfaction in breathing new life into a bike that has been dear to me. Plus, the e-bikes in that price range don’t offer the same all-aluminum body as my trusty MTB.
This project has been fulfilling in more ways than one. I find myself riding more in days than I have in months, which will increase my physical activity. I am also exploring more parts of the city by riding longer.
I would encourage you to give it a try, it will be a good mode to commute or just to enjoy the ride. Another benefit is that electric-assist feature eliminates the need for intense initial effort, making it easier on the knees.
Now, in future, I would possibly try to upgrade the system for more power and use a programmable controller. Or maybe if my urges take over and I feel the need to burn some money for fun can take it up to convert a Gypsy (another dream project).
