Yamaha PW S2 electric bike drive unit arrives with up to 75 Nm torque

The PW S2 has 250 W power and is rated for 36 V, assisting riders at up to 25 kph (~16 mph), with four assistance modes, including an Eco setting. Plus, it can deliver up to 75 Nm of torque and weighs just 2.85 kg (~6.28 lbs), which Yamaha claims gives it the best torque-to-weight ratio in the field. Not only is the device lightweight, 16% or 0.5 kg (~1.1 lbs) lighter than the PW ST, but it is also more compact than its predecessor, making it closer in size to the flagship PW X3 series.

Innovative features of the device include an automatic support mode for intuitive assistance when riding, and Zero Cadence Technology, meaning there is no delay in power from starting. Another advantage of the new model is a shorter bottom bracket shaft, measuring 22.8 mm (~0.90-in), for enhanced pedalling efficiency; the product also features a new ISIS bottom bracket shaft. Yamaha claims the device is reliable and maintenance-free. It is unclear how the new device compares to its predecessor in terms of noise generated. The Yamaha PW S2 is compatible with a front double chainring, which the company suggests will expand opportunities for e-bike manufacturers.

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