Yamaha Pedal-Assist Bicycle Mid-Motor Description And Specs

We take a look at Yamaha eBike mid-motors to see how they work.

Yamaha PW Series SE Mid-Motor

Yamaha PW Series SE Mid-Motor

Yamaha PW Series SE Mid-Motor pedal assist with four modes.Yamaha

Yamaha began to develop electric bicycles in 1989, and since 1993 has sold more than 2 million in Japan, and more than 4 million electric-assist bicycle drive units worldwide for use in the bicycles of other manufacturers. Yamaha is best known for its 66 years of experience in the production of motorcycles, and for its pianos and other musical instruments. The logo—three crossed tuning forks—reflects this heritage.

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.

Q-factor, the width measured across the outer faces of the pedal crank arms, is 168mm. This means your feet on the pedals will be no farther apart as you pedal than on a conventional mountain bike. The motor unit itself is 80mm wide.

Yamaha offers four units—the PW Series SE, PW Series TE, PW-X, and the PW Series 45, each of which delivers its pedal assist in four modes. Maximum assist cadence is the pedal rpm at which assist from the motor ceases. If the power unit continued to accelerate the bicycle beyond 20 mph, it would legally be regarded as a motorcycle.

Yamaha’s 500 watt-hour (Wh) 36-volt lithium-ion battery weighs 6.6 pounds, fully charges in four hours, and carries a three-year warranty. The commodity nature of lithium-ion batteries makes the weights, charging times, and other specifications quite similar from one make to another.

PW Series SE Urban/Paved Roads
Mode Eco+ | Eco | Standard | High
Assist % 50% |100% | 190% | 280%
Max Torque 70 Nm
Max Assist Cadence 110 RPM
Motor Weight 7.7 lb. (3.4kg)

PW Series TE is Yamaha’s third-generation drive unit, featuring four instead of the previous three sensors. Its fourth sensor detects inclines, switching automatically among the above support modes as riding conditions vary between level, uphill, and downhill, also providing special assistance for uphill starts.

Max Torque 60 Nm
Max Assist Cadence 100 RPM
Motor Weight 7.5 lb. (3.5kg)

PW Series 45 is a variant of Series SE for use where a maximum support speed of 45 kph (28 mph) is legal. The Series SE operating modes apply.

Max Torque 100 Nm
Max Assist Cadence 100 RPM
Motor Weight 7.7 lb. (3.5kg)
PW-X Unpaved/Mountain Trails
Mode Eco+ | Eco | Standard | High
Assist % 50% |100% | 190% | 280% | 320%
Max Torque 70 Nm, except EXPW 80 Nm
Max Assist Cadence 120 rpm (EXPW)
Motor Weight 6.8 lb. (3.1kg)