As mentioned in other articles, our Mid Drive motors mount in place of your bike's bottom bracket and replace your bike's crankset along with the front chainrings and derailleur (if you have front gears).
What does this mean?
When you install one of our Mid Drive motors you will only have 1 front chainring instead of the 1, 2, or 3 front chainrings which your bike had previously without the Mid Drive motor installed.
With 1 chainring now installed in front, you will no longer have the same range of access to the rear gears that you had previously with 2 or 3 front chainrings as shown in figure 2 below.
Figure 1. Accessible chain line gear pairings between the front and rear gears on standard bikes
Chainring Selection Process:
Since our Mid Drive motors mount in place of your bike's bottom bracket and replace your bike's crankset along with the front chainrings and derailleur (if you have front gears), the first step in the chainring selection process is to confirm which Mid Drive motor (BBS02 & BBSHD) you are going to check for fitment on your bike.
Note: BBS02 & BBSHD chainrings are specially designed to operate with the motor that it is intended to be used with (ie. BBS02 chainrings will work with BBS02 motors only and will not work with BBSHD motors and vice versa).
In order to do this, you will need to print out the motor fitment templates and test them as shown in the video below. This is also shown in our Bike Compatibility Quiz and is the final step, Step 4.
In order to determine which Mid Drive motor (BBS02 & BBSHD) along with which size you are going to print the motor templates in order to check for fitment on your bike. However, if you haven't taken our Bike Compatibility Quiz Steps 1 through 3 we recommend that you do this first before proceeding.
BBS02 750W: 68-73 mm
BBSHD 1000W: 101-120 mm
Once you have the correct template printed and have confirmed the motor fitment on your bike I am going to review the main things to consider when selecting a Mid Drive chainring for your bike!
1) Fitment and chainstay clearance - This is most important as the chainring needs to be able to clear your bike frame and chainstays as shown in the video.
2) Alignment with your bike's current chain line - Now that you have checked to confirm which motor will work with your bike frame and also confirmed which chainring sizes will work with your current bike frame (and not hit your frame or chainstays). You will now need to consider your chainring alignment based on the motor that you have selected and along with your bike's current rear gears and chain line.
Since with a Mid Drive motor you will only have 1 chainring installed in front, you will no longer have the same range of access to the rear gears that you had previously with 2 or 3 front chainrings as shown in figure 2 below. However, the good news is that you will no longer need to have this access to the lower (larger) gears once our Mid Drive motor is installed because you will have the equivalent of a 1+ horsepower engine added onto your bike! This being the case the motor is designed to reach all of your higher gears (smaller) in order to achieve the max speed since the motor provides more than enough torque to make up for any lower (larger) gears which you may no longer be able to access on your rear cassette as shown in figure 2 below.
Figure 2. Rear gear access with Mid Drive motor installed based on chain alignment
You will need to select a chainring with an "offset" as shown on the printable motor templates that is will allow you to reach as many gears as possible. A helpful fact, is that bike chains prefer to operate in a straight line however they have the ability to operate slightly out of alignment, how far from the center your chain is able to go in either direction before it falls off your sprocket or is unable to travel any further to one side is known as lateral flexibility. Lateral flexibility is what makes chains a good option for mechanical connections however this lateral flexibility is limited as shown in Figure 2 above (the length of your chain is going to play the largest part in the chain's lateral flexibility).
With this said you will want to make sure that you select a chainring that lines up as close as possible to the center towards your high (small) gears on your rear cassette. If you only have 1 gear in the rear of your bike then you would want to have your chain alignment be as close as possible to this gear and the Chainring which you select based on its designed size/offset will determine this.
3) Chainring size based on the riding that you are looking to do! (Speed vs. torque)
Last but definitely not least you will need to consider the chainring size.
Important Note: Everyone put the most focus on the chainring size however at the end of the day it is really the least important as the two most important aspects before chainring size are:
1) confirming that the chainring will fit on your motor/bike and not hit your frame
2) That the alignment allows you the largest possible range of gears
Knowing that times 1 and & mentioned above are most important, your front chainring size will also determine the operation of your motor. Our Mid Drive motors are designed to operate at certain cadences as described in this article so the motor will have a cadence which it is designed to operate at. It is hard for me to provide you with a tangible explanation as you would need to ride a bike with different size chainrings in order to feel the difference between them however our rules of thumb for selecting a chainring size based on the type of riding you are looking to do as outlined below. So take a look and see which category you fall into:
Overview: The larger the chainring the higher the top speed that you will be able to achieve while a smaller chainring will provide more low-end torque.
Max Speed: If you are simply looking to go as fast as possible then you will want to get the largest chainring that will work with your bike frame. Be aware that this will put more load onto the motor and you will have to make a more mindful and conscious effort to make sure that you are correctly shifting through gears when starting from stops or when climbing small hills. If you do not shift accordingly these larger front gears can overstrain the motors and result in blown controllers and fried motors.
Balanced riding: If you are looking for the best of both worlds then pick a chainring size in the middle based on your bike's fitment and depending on which way you prefer either higher torque or higher top-end speeds.
Steep Off-Road Riding or Heavy loads: This is for all of you serious off-road warriors or pedicab operators. With regards to this, the name of the game is really how low can you go, and what I mean by that is what is the smallest size chainring that will work with your frame and chain line alignment. A smaller chainring will provide you with more low-end torque which is so important when climbing steep hills at a slow speed or when riding with heavier loads.