Yamaha PW-X Electric Bike Motor Overview


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Hi guys, I'm doing a series on electric bike motors. These short guides will provide an overview and link to reviews with video and more details, related to specific ebike models. I welcome your qualitative and quantitative input to round them out because I mostly ride brand new models on relatively tame terrain and thus, do not have as much insight around different environments including steep climbs, cold or hot weather, and long term wear and noise. Thanks for your input!

Following are a few relevant video interviews with companies who are using the PW-X and Yamaha themselves:
The Yamaha PW-X mid-drive electric bike motor builds on the original PWseries that was quiet, lightweight, and efficient. Many of the shops I visit while filming reviews tell me that the PWseries has been one of their most reliable drive systems to date. It stood apart from Bosch, Brose, and Shimano because the standard 1 to 1 chainring could be upgraded to two or even three chainrings as seen on the Easy Motion Rebel Gravel. This option significantly expands the gear ratio, allowing riders to climb more easily but also reach and maintain higher speeds. The trade-off is increased weight and drivetrain complexity with potential for mashing and wear because the motor system does not offer shift detection. Shifting works fine if you reduce pedal force for a moment just before and during a gear change because the motor listens closely for pressure change and will ease off almost instantly. The PW-X motor has a lot in common with the PWseries but offers more torque power, up to 80 Newton meters verses 70 Nm on the standard PW, as well as higher pedal cadence support. While the PWseries would cut out at roughly 100 crank rotations per minute, the PW-X can reach roughly 120 RPM before fading. In my experience, it's not quite as confident at higher RPM as the Bosch Performance Line CX or Brose S, but it's a big step up nonetheless. Higher cadence support allows you to downshift in anticipation of a steep hill without losing motor support and ultimately slowing down. For someone like me, with sensitive knees, this is a big deal. I like to spin fast even when not climbing and was frequently disappointed and frustrated by the PWseries motors because of their limited support... especially because the motor was fitted to bikes like the Rebel Gravel which are designed for high performance fast-pedaling use. The power curve has been smoothed out and a new drive mode EXPW "Extra Power" is well suited to steep climbs and technical environments. Another big upgrade with the PW-X is the number of pawls and ratchet teeth inside that reduce stroke distance and engagement time for the motor to kick in. The pawls are in pais and offset, so one pair is in contact (shown in red in the "Quick Response" image below). The PW-X offers four pawls with 1.5x the number of teeth, reducing backlash by roughly 30% according to the company. Yamaha has marketed their motors as offering "zero cadence starts" that provide critical assistance on varied terrain. This comes back to the motor controller responsiveness and heavy reliance on pedal torque as a rider input signal, and now it's even faster because of the increase in pawls. In addition to power and internal hardware upgrades, the PW-X is also 13% smaller (being narrower and shorter), about 0.84 lbs (380 grams) lighter, and has moved from the square tapered spindle used on the PWseries to splined ISIS standard. The motor weighs roughly 6.76 lbs (compared to 7.6 lbs for the PWseries). It's rated similarly to the PWseries at 250 to 500 watt output depending on level of assist and rider input. It also has an impressively narrow Q-Factor of 168 mm, the narrowest of the big manufactures for the 2018-2019 season. Wider cranks can be added for fat bikes and plus sized frames but it's nice to also go narrow in the case of a cross country or road model.
  • Power range: 250 to 500 watts
  • Maximum assist: 320%
  • Torque output peak: 85 Newton meters vs. 70 Nm
  • Maximum cadence support: 120 rotations per minute vs. 100 RPM
  • Spindle design: ISIS standard vs. square tapered
  • Spindle length: 135 mm
  • Q-Factor: 160 mm
  • Number of pawls: 4 vs. 2
  • Number of teeth: 24 vs. 16
  • Weight: 6.83 lbs (3.1 kg) vs. 7.67 lbs (3.48 kg)
  • Size and volume: 220 mm length, 155 mm high, 80 mm width, 13% smaller than PWseries
  • Assist levels: +ECO, ECO, STD, HIGH, EXPW
  • Battery compatibility: 400 or 500 watt hour 36 volt

@Mikey-, of Blue Monkey Bicycles, has created an excellent video covering the PW-X motor and I have embedded it below. He got a sample unit and was able to show the guts, which is pretty cool! The motor image below and this video are being shared with permission <3

I have also created a video guide for the new Yamaha PW-X display panel which is posted just below. The new display is tougher than than the PWseries LCD and positioned behind and slightly below the handlebar to reduce trail damage. It's not removable and the LCD display is smaller, but it does offer some color to communicate the level of assist as well as a remote button pad for easy operation.

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