Picking the right chainring for your mid-drive motor whether you have a BBSHD, BBS02, TSDZ2, or CYC Photon, Stealth, or X1 Pro is important but can be tricky.  There are a lot of factors to consider in getting the one that will be the best all around.  Let's take a look at some of the more important ones.
Close Up of Mid-Drive Motor
Lekkie narrow/wide chainring on BBS02
With a mid-drive motor you may have fewer gears
The front sprocket by the pedals is called a chainring.  With a mid-drive motor you take off your front chainring(s) with the cranks and bottom bracket and slide in the motor with its own chainring.  If you had more than one chainring you now only have one.  Let's say you had 3 chainrings up front and 9 cogs on your rear wheel.  
That is a total of 27 combinations or speeds.  With the mid-drive motor you typically have just one chainring which means your 27 speed is now a 9 speed.  This is not as bad as it sounds in fact in some respects it is desirable.  Riders find that they need fewer gears with electric assist and it is nice having fewer gears to shift through. 

If your bike originally had 3 gears up front and they were 52 tooth, 42 tooth, and 38 tooth, you might want to pick the middle or gear or 42 tooth chainring as the best all around.  If you still want a wide range of gears, especially low gears then you can trade out your rear cassette for a wider range cassette and have the full range you need.  You can read more about that here.

As it turns out most newer mountain bikes and now many city and road bikes have only a single chainring up front and a wide range cassette in the back.  This is known as a 1x drive-train.  So adding a mid-drive doesn't require any of the trade offs mentioned above.  In fact if you have an older bike you can look at going to a mid-drive to be a 1x drive-train upgrade as well.

If you really want more than one chainring it is possible.  It is actually common with the TSDZ2 motor by installing a different chainring on either side of the 110 BCD spider.  It is less common with Bafang but is still possible.  The problem is many front derailleurs won't go out far enough to reach the outer chainring.  Since the TSDZ2 doesn't stick out quite as far as the Bafang motors more front derailleurs will work with the TSDZ2.  If you just want to have it on one or the other based on city or mountain riding then you can move it by hand before you start out. In fact racers would shift by hand in the middle of a race before the invention of the front derailleur.
The TSDZ2 comes with a 110 BCD spider.  You simply mount a different chainring on either side of the spider. After-market spiders are available for the BBS02 and BBSHD as well and dual chainrings can be used with them as well.  However, this is rarely done because of the cross-chain problems that arise from not using a single offset chainring.
TSDZ2 42T narrow/wide offset chainring
TSDZ2 42T narrow/wide offset chainring
TSDZ2 30T narrow/wide chainring
TSDZ2 30T narrow/wide chainring
TSDZ2 110 BCD dual chainring selection
TSDZ2 110 BCD dual chainring selection
Why are some mid-drive motor chainrings offset?  Each mid-drive motor comes with a chainring, usually steel and between 42 to 46 teeth.  This is usually a good size for all around riding and also 42 teeth is the typically the smallest you can go and have the chainring offset to return your chainline as close as possible to your original chainring(s).  This simply means that the motor pushes your chainring mount point to the outside and by dishing or offsetting the chainring they can move it back inboard closer to where your original chainrings were.  Chainrings smaller than 42T can't be dished because they would hit the motor housing so they are further outboard and the chainline will be off.  This is not a problem on many bikes but you want to try to keep the chain as straight as possible.  42T is simply too big for many mountain bikers so they get a smaller chainring for overall lower gearing and the chainline is still fine through much of the range but is more cross chained in the lowest (large) gears on the rear wheel.  Recently Lekkie introduced a 40T chainring  for both the BBSHD and BBS02 with great offsets achieved by replacing the gear reduction cover on the motor.  These are very nice but are more expensive and harder to install.

What size chainring is ideal?  The ideal chainring size can be illusive because you are making tradeoffs. The Bafang motors want to run fast and perform at their best with smaller chainrings while the TSDZ2 motors tend to top out at a cadence of 90 to 100 so a somewhat larger chainring for riders that like a fast cadence can be better.  If you just want overall lower gearing for mountain biking a 30-38T chainring is ideal.  However, if you have a Bafang with chainline issues then you may want to go with a 42T and make sure you have ultra-low gears in the back in the 40-50T range.  If you are a speed demon and want to feel like you are contributing and getting a good workout at higher speeds you may want a 46-52T chainring.  I say "want to feel like you are contributing" because even if you are pedaling very hard the wind resistance at high speeds is so significant that the motor will be doing the lions share of the work but you will still get a good workout.
Lekkie 40T chainring with included motor gear reduction cover
Lekkie 40T chainring with included motor gear reduction cover
Lekkie family of narrow/wide chainring upgrades for Bafang mid-drive motors
Lekkie family of narrow/wide chainring upgrades for Bafang mid-drive motors
The size of the chainring you should use for your mid-drive motor ebike conversion depends on various factors, including your desired riding style, terrain, and motor specifications. Here are some considerations to help you choose the appropriate chainring size:

Motor Power and Torque: Different mid-drive motors have varying power outputs and torque capabilities. Higher-powered motors, like the Bafang BBSHD or CYC X1 Pro or Stealth, can handle larger chainrings, providing more speed and torque. Smaller motors, such as the CYC Photon, Bafang BBS02, or TSDZ2 may work better with smaller chainrings but can still use larger chainrings when not under heavy loads caused by hills, headwinds, and weight.

Desired Speed and Cadence: If you prefer faster speeds and higher cadence pedaling, a larger chainring may be suitable. A larger chainring allows for higher top speeds, but it will require more effort to pedal and may lug the motor at lower speeds. Conversely, a smaller chainring provides more torque and ease of pedaling at lower speeds but limits the top speed. Keep in mind that most mid-drive motors can go much faster with a throttle than it is possible for you to peddle.  A large chainring will allow you to pedal and still get exercise at faster speeds.

Terrain and Riding Style: Consider the type of terrain you'll be riding on. For hilly or mountainous areas, a smaller chainring can provide better climbing ability and low-end torque. On flat terrain or for more speed-oriented riding, a larger chainring may be preferable.

Gear Range: The choice of chainring size also affects your overall gear range. A larger chainring paired with a wider range cassette at the rear can provide a broader gear range, suitable for various riding conditions.

Frame Compatibility: Ensure that the chosen chainring size is compatible with your frame's clearance. Some frames may have limitations on the maximum chainring size due to chainstay or tire clearance.

It's worth noting that the mid-drive motor kits typically come with a default chainring size. However, these can often be replaced or swapped for different sizes to suit your preferences and riding needs.

Ultimately, there is no one-size-fits-all answer, and the ideal chainring size for your mid-drive motor ebike conversion depends on your personal preferences, riding style, and the specific characteristics of your motor and terrain. It can be helpful to consult with experienced ebike enthusiasts, local bike shops, or the manufacturer's recommendations for guidance on selecting the appropriate chainring size for your setup.

Should I upgrade my chainring?  This question may be answered for you if you choose a different size chainring than the one that comes with your motor.  If you want higher or lower overall gearing you need an upgrade.  Even if you decide you actually want the size that came with your motor, you may still want to get an upgrade.  The upgrade chainrings made by Lekkie and others are typically CNC 7075 T6 hardened aluminum and are lighter, better looking. They also have a significant advantage by using a narrow/wide tooth profile.  This means that every other tooth is wider or narrower to fill the entire space in the outer and inner chain links.  This has the advantage of holding the chain onto the chainring so that it doesn't come off.  If your bike had a front derailleur then you probably never had this happen because the front derailleur holds the chain on.  Without the front derailleur you may find your chain frequently or infrequently coming off of the chainring.  This is no fun.  Some bikes never have that problem.  We sometimes advise that want the size of chainring that comes with the motor to just run with the stock chainring to start out and then if they have their chain coming off they can upgrade to a narrow/wide tooth profile chainring to help solve the problem.  Chainguides can also be used and if your rear derailleur has a clutch that will also help to keep the chain from popping off.

What about IGH hubs?  All of the above applies to your chainring consideration except if your chain is properly tightened it won't ever pop off.  You may still want a chainring upgrade to get higher or lower overall gearing or to trim weight and have a better looking bike.


  • steven

    I recently installed a Bafang BBSO2 motor kit. As you know I now have only one chain ring in front instead of my 3 as before. I am worried if I ever lose the motor system for any reason I will not be able to get my trike home as there are many hills which I can not climb with the standard Bafang chainring. At one time I had a 22T gear on front I called Grandma. I would like to have it installed on the outside of the Bafang ring so if I ever have a failure I can manually slip the chain over to it and climb the hills as in the old days. Have any idea how this might be done?
    Electrify Bike replied:
    You can replace the right Bafang crank with a regular crank, spider, and chainring. A BCD104 spider can take a 30T chainring. An even better solution would be to upgrade your drivetrain to a Box Two, Three, or Four (we sell them). They have a huge 50T grandma gear in the back that let’s you climb anything.

  • Rob O'Driscoll

    I have a motobecane e mtn bike with shimano drive it has a 34 tooth front drive sproket. 4 bolt bcd is as close as I can measure 104.75 I would like to go to a 38 tooth. Does anyone make one that size?
    Electrify Bike replied:
    Yes, BCD104 goes down to 30T.

Leave a comment

Please note, comments must be approved before they are published

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.