It is remarkable that a powerful brushless electric motor plus two stages of low-noise reduction gearing with control electronics plus torque sensing can be built into these narrow drive units that anyone can easily lift with one hand. To reliably handle the rider’s weight and pressure on the pedals, the pedal shaft and its bearings must be strongly supported. The drive unit case takes a “clamshell” form of cast-aluminum halves, held together by screws. Within these the bearings for pedal and gear shafts are supported, along with an electronics board to switch direct current (DC) from the battery into the complex pulsed form required to drive the motor. Because pedal-assist bicycle marketing at present emphasizes “lifestyle,” technical details must be gleaned from other sources. One example is the gear reduction from the electric motor’s shaft (which turns at something like 3,500 rpm) to the pedal crank, cited by one source as 45.77:1. This high ratio agrees with comments from independent reviewers, describing the Yamaha units as aimed at placing peak motor performance at the lower end of the cadence range, from 65 to 80 rpm.