WHAT DOES IT ALL MEAN?
There are a lot of terms used in the electric bike world that can be confusing, especially if you are unfamiliar with them. Some of the terms might even confuse an electrical engineer. We love e-bikes and want everyone to enjoy them, too, and knowing more about them makes your rides more enjoyable and can also help you understand our reviews and help with your next bike purchase.
Here’s a breakdown of some of the most commonly used e-bike terms with explanations to hopefully make diving into the e-bike market easier to understand and enjoy.
Ampere hours, generally shortened to amp hours or Ah, are a measure of battery capacity. The larger the number of amp hours listed, the more energy is stored in the battery. It’s a measurement of how many hours a battery can put out 1 amp.
Any time you fully discharge then fully recharge a battery, it’s considered a charge cycle. Any time you partially discharge a battery, say by 33 percent (i.e., there’s 77 percent of the charge still left), it’s a partial cycle. In this case, it is 1/3 of a cycle. Batteries are rated usually for between 500 to 2000 charge cycles before they will no longer have enough capacity to be useful. It’s worth considering this when you buy a bike; ask if replacements may be available in a few years. Companies like Bosch and Yamaha have made the same form-factor batteries for many years, so even an older bike with one of those systems can get new life through a new battery.
There are so many places that any bike can house its powerplant. A majority of mountain bikes rely on mid-mount motors (see below), whereas some bikes rely on motors found in the hub of the wheel. While there are a few fringe designs that locate the motor in the front hub, the majority are found in the rear hub. Hub motors are generally rated at 350–750 watts. There are more powerful motors, up to many thousands of watts, but 750 watts is the federal legal limit.
They can be direct drive, which can offer regenerative braking. Regenerative braking slows down the motor, and at the same time puts some energy back in the battery. Don’t expect to recharge your battery to any significant degree with regeneration, but it is nice on long downhill rides to help maintain a reasonable speed.
The other type of hub motor uses internal planetary gears to turn the hub and make the wheel turn, and the bike move forward. These are often smaller than an equivalent-wattage direct-drive hub and can be quieter, but offer no regenerative braking.
Most modern e-bikes, at least the ones sold in North America and Europe, use lithium-ion batteries. This type is lightweight for its size and energy density, and they’re reliable and safe. The risk of them catching fire, especially while charging, is infinitesimally small these days. The ones that we read about catching fire are almost always off-brands who use cheap, poorly made batteries.
Mid-drive motors are mounted at or near the bottom bracket (over the pedals). These have an advantage with a multi-gear drivetrain, because riders can control the torque by shifting gears. These are often 250–350 watts instead of higher wattages.
They are levels of assist on most e-bikes most often referred to as Eco, Standard, High or Turbo, or could be numbered (e.g., level 1 is the lowest level of assist, 5 or 9 may be the highest).
A Newton-meter, often abbreviated as N/m, is a measure of torque. It’s the force of one Newton (the measurement of the force needed to accelerate 1 kilogram of mass at the rate of 1 meter per second squared in the direction of the applied force) applied perpendicularly to the end of a moment arm that is one meter long.
Pedal assist means that an electric motor helps you pedal when you pedal. Without moving the pedals, you will get no help from the motor. In the U.S., there are three classes of bikes, both are pedal assist. Class 1 offers pedal assist up to 20 mph and Class 3 offers pedal assist at up to 28 mph.
A motor’s output power is measured in watts. The number of watts is stated in the nominal amount, not the peak output. A 750-watt motor may put out 1200-watt peak, but that doesn’t make it more than the legal limit. The legal limit is based on the nominal output of the motor.
The Q-factor is the distance between the pedals measured parallel to the bottom bracket. Up until the last few years, many mid-drive motors had a much wider Q-factor because of the motors, but modern motors have been shrunk down to have a Q-factor similar to a regular bicycle.
Range is the distance you can travel with your bike before you’ve used up all the stored energy in your battery. There are a myriad of factors at play in figuring out your range. First, you have to factor in the size of the battery, wattage of the motor and what mode you’ll be riding in. You also have to add in your weight and the weight of the bike. Finally, you have to see what surfaces (e.g., street, dirt, gravel) and grades of hills you’ll climb, and if there’s any wind. It’s really complicated. Manufacturers want to assuage your range anxiety by telling you the ideal range for the bike. Call us cynical, but it seems that to come up with their advertised range figures, most manufacturers rely on a lightweight test rider pedaling in Eco mode in an area with no hills and with a slight tailwind everywhere they ride. In essence, that’s why the advertised range numbers always look so good—and rarely match up with real-world riding.
The older type of battery technology is sealed lead-acid (also called SLA) batteries. These are usually 12 volts, very heavy and don’t have a very high capacity. We’ve seen some systems with lead-acid batteries connected in a series to make a 24-volt battery to allow for a faster motor. Electric bikes that use SLA batteries are sold by the millions every year in China, but are more rare here.
This is the percentage of the rider’s pedal input compared to the output of the motor. Eco may be as low as 50–75-percent support, whereas Turbo can offer up to 350-percent support.
Torque is measured in Newton-meters (N/m). It is rotational force, where power is linear force. Think of torque as how much work a motor can do versus power that is the rate of work that can be done. A motor with a lot of torque (e.g., Yamaha’s PW-X2 motor that produces 80 N/m of torque) can get you moving quickly and make climbing hills easier, where the power (250 watts) sustains that speed and helps move you along at whatever speed you want to go.
This is the potential force of power flow from the battery to the motor. It’s like water flowing through a hose—the higher the voltage, the more electrons can flow to the motor so that the motor can do its work. Typical e-bikes use a 36- or 48-volt system.
Walk mode is a really handy feature that is designed to make it easier to hike a bike up a section that may be too steep or difficult to ride through. It can power the bicycle at a walking pace, but usually doesn’t offer enough power to make a relatively heavy bike able to carry some of its own weight.
Power is a measure of the rate at which energy flows, and in electricity, it is measured in watts, abbreviated as W. Watts are sort of like the miles-per-hour measurement of the electrical world, they tell you how fast the electrons are speeding down the highway. The higher the wattage, the faster you’ll use the energy stored in the battery.
Watt hours, or Wh, are a measurement of overall battery capacity by multiplying the amp hours by the voltage (usually rounded off). For example, a battery with a rated voltage of 36 volts and 14 Ah has a capacity of 500 Wh (rounded down from 504).