The message below I copied from internet.

BMC is an established, respected maker of electric motors.  This is their new high power 600W internally geared bicycle hub motor, electrically optimized for high speed performance.

The gearing allows the motor to spin about 5 times faster than the axle.  This has many benefits compared to direct drive hub motors that spin the axle at motor speed.  Electric motors are more efficient and torquey when they spin at higher RPMs.  This motor has the power of a much larger direct drive motor.  It is only 7.5" in diameter, and delivers big power and the torque to help with even steep grades.  The gearing also allows the motor to spin freely when coasting.  Regular direct drive hubs and add drag when you choose to use pedal power only or coast. 

• Standard 6 bolt disc brake rotor mounts
• Front or rear drive hub, please make your selection in our checkout function
• The kit includes 36/48V 30A controller.  It can be switched from 36V to 48V to match your battery pack.  It is great if you have batteries of different voltages or plan to upgrade later
• The controller features IRFB 4110 Mosfets.  In lay terms, it is way over engineered for its rating, which increases reliability.
• Includes half twist grip throttle
• 7 speed freewheel cogset with 11-30T so you can have the high gear you want for pedaling and a wide range, too. 
• One year warranty
• Price is for a 26" wheel build.  Sun Rhyno Lite double wall eyeletted rims and 14g US made stainless steel spoke with brass nipples.