Converting your own bike into a powerful electric bike
05/10/2026
Power-e-bike offers for sale different versions of the electric bike motor RH205 from “Nine Continent” and it is not simple to choose the right one, the one that will suit your use.
We will see in this article that power-e-bike gives us some information allowing a basic choice, but in my view a certain amount of information was missing, information I learned as I went along with my use, as well as through my initiation into the field of electric assistance.
A few acronyms to start with, which will simplify reading:
9C: Nine Continent
PAS: Pedal Assist System, pedalling assistance
E-bike: electrically assisted bicycle
Limn: Lithium Manganese, a type of lithium battery
That is done :D!
For information, I bought my electric bike motor kit from power-e-bike in August 2014 and my specifications were as follows:
-Being able to go back and forth between my workplace and my home, 4 km on gravel dirt paths and on the road
-Being able to hold 30km/h uphill, notably on a 10% portion over 1.5km, knowing that morning traffic drives rather fast.
-At the time I chose a 280-380 version, midway between torque and max speed as shown in this table.
The first thing the site shows us is this table, which in my view allows a somewhat too brief approach, because it shows us that the choice boils down to an even split between torque and max speed.
Once fitted and in use, we realise that the electric bike motor is very torquey at the start, that is where it “hauls” because that is when you feel the power through the e-bike’s acceleration. We also realise that this acceleration decreases as speed increases, so that at 20~25km/h the acceleration has flattened out.
We will see that ultimately, the difference between the motors is mostly speed.
This is illustrated very well if you use a free online simulator on the Canadian shop of Grin Technologies:
This is a “at 100% throttle” curve of the 9C RH205 electric bike motor in 280-380 (8 copper turns per pole), where the torque (in blue) is very strong at the beginning, then decreases progressively, while (in black) the air and rolling resistance efforts increase.
We see that at 100% throttle, the mechanical power of the motor (in red) equals the resistance efforts (in black) at 31.5km/h.
We can also see that the torque goes down progressively until about 22km/h where it drops off more rapidly.
We thus see that with this configuration (9C 280-380 motor, 27 amp controller) as well as a LiMn 36v 15Ah battery, the motor alone will propel us up to 31.5km/h and the battery will last 50km.
In this second simulation, we can compare the 280-380 motor (8 turns/pole) and the 350-480 (6 turns/pole, the fastest at POWER-E-BIKE, called 2806 at Grin), we see very interesting things:
-With equal battery, controller and load (26′ MTB and weight of the mountain biker + bike at 100kg), the torque of the “fast” motor is only about 4% lower than the torque of the torquey motor up to about 22km/h then comfortably overtakes the latter, which collapses. (The blue curves)
-The torque of the “speed” motor does not collapse at 22km/h but at about 34km/h.
-Efficiency (that is, the ratio between the energy still consumed from the battery and the mechanical energy returned by the motor), on the other hand, is always in favour of the torquey motor. (The green curves)
-At this speed of 31km/h, the speed motor at 100% is still accelerating and consumes a lot. You can reduce its consumption by reducing the throttle, and at equilibrium at the same speed, the consumptions are comparable and the differences not significant.
Nevertheless, in France you can only ride an e-bike up to 25km/h in assistance mode. With this very handy tool, suppose we want to ride in assistance mode staying at the limit the law imposes on us, namely at 25km/h max. You can play with the “throttle” slider, which more or less means “throttle percentage”.
We thus see that the “torque” motor needs 75% to maintain 25km/h whereas the “speed” motor is at 58%.
We note a more than marginal difference in consumption, namely 5.3A for the slower and 5.5A for the faster.
We can thus see that at this pace, theoretically on the flat and with this battery, one motor as much as the other will manage about 69km without overheating problems.
Note well here that the figures are given here as an example, and that a variation in weight, battery (voltage, chemistry, capacity), or controller (17A, 22A, 35A, …) will change these figures. They will nevertheless not change the conclusions, which are as follows:
What will really make the difference is the power reserve.
We can therefore also say that ultimately, it is a difference in maximum speed that should really decide your choice.
I made this remark to POWER-E-BIKE regarding their table, which gives equal importance to the difference in torque and speed. In reality, it is the power reserve (or the speed) that will mainly change, then come efficiency and starting torque in lesser importance.
Without flooding you with data and simulations, we realise that a slower motor will be all the more efficient (in terms of electrical consumption) if you accompany it by pedalling.
Note, however, that it is not legal to ride such a machine on public roads without limiting the power, whether road or path, because if you do not limit the power of such a vehicle (9C motor, 27A controller, 36V battery), it develops nearly 1 kilowatt, that is, the power of a moped…
