Most standard bikes do not need extension cables unless you install your setup in a unique way (e.g. choose to mount your battery somewhere other than your bike's downtube).
Trikes and recumbents typically need extension cables, most likely they require Speed Sensor Extension Cables and Battey Extension Cables (depending on where you mount the battery) and may also need Display, Brake/Throttle, and/or Main Wiring Harness Extension Cables.
The exact extension cables that you will need depend on your specific setup, so we are not able to tell you what extension cables you will need as it depends on your unique setup.
Below we provide you the stock cable lengths that come with the Bafang BBS02/BBSHD motor kits.
This information will allow you to determine whether you need extension cables for your specific bike setup:
There are 4 leads that come straight out of the motor assembly: Speed Sensor Lead, Main Wiring Harness Lead and Battery Leads. All of these cables are approximately 18 inches.
The Main Wiring Harness Cable is a separate cable that connects to the Main Wiring Harness Lead coming from the motor (18 inches as described above) to the handlebar components (display, brake levers, and throttle). This Main Wiring Harness Cable is a total length of approximately 41 inches. This Main Wiring Harness Cable (41 inches) connects to one of the of the motor leads (18 inches). Therefore the stock cables that come with the motor kit provide you with a total distance of 59 inches from the motor to the display cable, throttle cable and brake lever cables.
The cables that come from the Bafang Mechanical Ebrakes are approximately 6.5 inches. These cables connect to the Main Wiring Harness.
The cable that comes from the Throttle is approximately 6.5 inches. This cable connects to the Main Wiring Harness.
The cable that comes from the LCD Display is approximately 8 inches. This cable connects to the Main Wiring Harness.
The leads that come from our batteries are approximately 11 inches. The battery leads connect to leads coming from straight from the motor (18-inch leads). Thus the stock cables that come with the kit provide you with a total distance of 29 inches from the battery to the motor.
You can always order extensions if you realize you need them after you begin the install process!