The technology that drives E-bikes arrived so quickly that even those of us who can see at a glance how much a bike should cost, what it should weigh, and how to service its parts may be a bit hesitant when it comes to assessing a new generation of E-parts. Here’s a primer on the language of E-MTB, in alphabetical order.
Amp-hours Amp-hours (Ah) are a measure of battery capacity—so the more Amp-hours on offer, the longer each charge cycle will last. Good quality E-MTB batteries offer between 11 and 14Ah.
Charge cycle An emptying and refilling of the battery. Projected battery life is usually expressed in terms of charge cycles, so a battery with 1,000 charge cycles should last through 1,000 recharges. While there’s some decrease in capacity over this time, 1,000 charge cycles would usually enough for years of use.
Hub motor Describes any kind of E-bike where motor sits inside a hub, often in the rear wheel.
Lithium-ion battery There are many different batteries available for E-MTBs, but Lithium ion (or Li-ion) batteries are typically the best-performing, being light, and with a long lifespan. Lithium-ion batteries are used in a wide range of rechargeable devices, including mobile phones and cameras.
Mid-drive motor Sometimes called a bottom bracket motor, this motor is located centrally in the bottom bracket, as opposed to in the hub. This is becoming a popular choice for E-MTBs as it provides low, centred weight distribution, intuitive ride feel, and easy wheel removal compared with hub motors.
Mode A level of motorised support provided by a pedal-assist E-MTB, selected by the rider using a handlebar-mounted switch and displayed via a unit mounted to handlebars. Shimano STEPS E8000, for example, offers three drive modes: Eco, Trail, and Boost.
Newton metre (Nm) A measure of torque, force that is applied to cause rotation (see Torque).
Pedal-assist Pedal-assist E-bikes sense the torque or cadence of the rider and respond by increasing power output. They differ from throttle-powered E-bikes, which operate more like mopeds, and do not require pedalling. Pedal-assist E-MTBs have a natural ride feel, are legally classified as bicycles in most countries, and are the most common type of E-MTBs produced by major bicycle manufacturers.
Power Measured in Watts (W), this is the amount of work that can be done by the E-bike system. Most pedal-assist E-bikes sold in Australia are limited to between 200 and 250W by law. The more watts, the more powerful the system is. One Horsepower is 750W (see Watt).
Q factor Put simply, the distance between the pedals measured parallel to the bottom bracket. On mid-drive E-bikes and E-MTBs, Q factor has, in the past, been wider to accommodate motors. Now, systems such as Shimano STEPS offer the same Q factor as standard mountain bikes.
Range The distance or time a battery will last under any given circumstances. Range is determined by battery capacity, and affected by the total weight of bike and rider, the terrain (hilly, flat, downhill), and ride mode. Range changes according to these circumstances, and is usually dynamically displayed on a handlebar-mounted computer.
Support ratio In pedal-assist E-MTBs, the percentage of a rider’s pedalling input that is provided by the motor. This changes at different modes. For example, a low mode might support 70% of a rider’s pedalling power, while a high mode might support over 250%. Batteries last longer at lower support ratios.
Torque Measured in Newton metres (Nm), torque is a measure of force applied to cause rotation. Torque specifications for E-MTBs (for example, 70Nm) refer to the maximum force that can be applied to the rear wheel by the motor.
Voltage In simple terms, this refers potential force of power flow from battery to motor, similar to the way water runs through a hose under pressure.
Walk mode A low-power mode to assist with walking the bike on stairs and around tight corners, for example.
Watt An important unit of measurement of power produced by a system and, along with voltage, determines how fast an E-MTB can go.
Watt-hours A measure of overall battery capacity found by multiplying Amp-hours by voltage (then rounded to the nearest 50 or so). So, a battery with a rated voltage of 36V and 14Ah is said to have a capacity of 500Wh (36x14=504).