Gear Issue: Performance e-bike basics

Published March 30, 2020 10:35AM

E-bikes will inevitably become a higher percentage of the bikes on the roads and trails near you. While the technology is far more refined than a decade ago, e-bikes are still in their infancy. As consumers clarify what they want and manufacturers figure out how to deliver it, development continues apace.

And while aesthetics will constantly change year to year, the most important technological development is largely focused on three characteristics: versatility, power, and weight. E-bikes of interest to longtime road riders tend to be pedal-assist only, either class 1 (motor assist only up to 20 mph) or class 3 (28 mph max). Class 2 e-bikes have a throttle, don’t require the rider to pedal, and top out at 20 mph.

Performance e-bikes for road and gravel riding fall into one of two general categories. Mid-motor class 3 e-bikes offer full-time motor assist. These tend to have a single chainring not fixed to the crank; it rotates at a different rate than the feet. These bikes continue to get lighter thanks to technological improvements that drop 9-pound motors like the Bosch Performance Line down to 6 pounds, while producing more torque.

However, the requirement for both high-torque and high-battery capacity to maintain constant assist up to 28 mph means that 33 pounds is about as light as the bikes get. High-end e-bikes have 36-volt batteries made up of lots of single lithium-ion cells banded together; the weight of the case around those cells may vary, but all batteries with a given capacity will weigh essentially the same. A 500 watt-hour battery weighing 6.5 to 8 pounds is standard for this type of bike.

The other general road/gravel performance e-bike type is lighter (under 31 pounds) and provides assist only up to 20 mph or even 15 mph. These superlight class 1 e-bikes have essentially no greater drivetrain friction than a standard bike when the motor is not running, and are ideal for riders who can keep up with their group on the flats and only desire motorized assistance when climbing or accelerating.

The battery is generally used less over the course of a ride and is often hidden on or in an oversize down tube. It has about half as much capacity (and weight) as high-performance class 3 road/gravel bike batteries. The motor offers less torque, can be either in the bottom bracket or in the wheel, and weighs considerably less than a class 3 bike’s mid motor. The Spanish Ebikemotion X35 36V/250W rear-hub motor and 250 Wh battery system weighs 7.7 pounds including wiring and accessories and is supposedly “totally transparent for the user when [the] motor is switched off.”

Many performance road/gravel e-bikes of this latter type allow easy removal of the battery and motor, converting it to a standard, lightweight carbon bike. With a hub motor, it’s apparent why substituting a standard wheel results in a normal drivetrain. However, since mid-motors generally add frictional drag by turning planetary gears driving the chainring at a different rotational frequency than the crank arms, it’s trickier to offer a mid-motor e-bike that can transform into a free-pedaling lightweight racing bike. One German manufacturer, Fazua, offers such a system.

The entire Fazua Evation mid-drive system weighs 10.1 lbs. It provides 250 watts of power and up to 400 watts for short bursts. Remove the motor packaged with the 36V, 252 Wh lithium-ion battery to drop 7.3 pounds off the bike. A three-lobed key on the bottom bracket gearbox plugs into the motor shaft. The gearbox contributes the remaining 2.9 pounds of system weight, accepts standard cranks (yes, a double with a front derailleur), and spins freely with the motor removed.

Perhaps more importantly, after a year of delays waiting for American regulatory approval, Fazua Evation motor drives are now available on a wide array of bikes in the U.S. That means versatility, power, and weight reduction are all coming to the U.S. market this year.