HOW TO UPGRADE THE CHAIN RING ON YOUR SUPER 73
As your electric bike approaches its top speed, your pedaling may feel like it is delivering less torque to the rear. At top speed, power stops being sent to the motor. Your pedaling will then be spinning in motion. A quick and inexpensive fix for this is to increase the size of your chain ring.
Most bike shops can install a larger chain ring very easily for a small fee, or you can do it at home.
Step 1: Remove the chain guard. With pliers, bend the tab that holds the chain ring out of the way.
Step 2. Remove the old chain ring and chain and replace it with a larger chain ring. The type of chain ring used on the S-2, R, and Rx is 108 BCD with teeth. We recommend upgrading this to 46 teeth.
Step 3. Increase the length of the chain to fit the larger ring. For example, for the S-2 to upgrade to a 46 tooth ring, we created a 21-link chain from two chains. A chain link removal tool is needed or a bike shop can do this for you while you wait.
Step 4. Install the new chain.
You will now feel more torque as you pedal in the higher speeds. You will be able to keep the bike moving forward without motor assist after you reach the maximum allowed motor speed. For a lot of people, this feels more natural, enjoyable, and safer than having the pedals spin in place. On the flip side, a larger chain ring also means it takes more leg muscle to start the bike forward from a stop - but most people use the throttle for this.
We sell 46-tooth chain rings here.
The following info on crankset length and chainring tooth count for stock Super73 Bikes (taken directly from their website):
You can read more information about chain rings and other parts in this article by Super73Nomad.