Yamaha has unveiled a new drive unit for electric bicycles, the PW S2. The motor can assist e-bikes at up to 25 kph (~16 mph) and deliver up to 75 Nm of torque. Plus, the compact device is 16% lighter than its predecessor, the PS ST, weighing 2.85 kg (~6.28 lbs), giving it a high torque-to-weight ratio.