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It helps to know what all the funny-sounding words 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 we want everyone to enjoy them, 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. To that end, we’ve compiled the following list of commonly used e-bike and bicycle terms that we frequently use in our reviews, along with their explanations, to make it easier to understand.
Amps or Amperes
An ampere is the base unit of electrical current. An ampere is equivalent to a charge of one coulomb per second.
The power of the circuit is given by the following formula:
P (Watt) = V (Volt) × I (Ampere)
Rearranging the above equation, we can calculate the value of electric current as follows:
I (Ampere) = P (Watt) / V (Volt)
A common example is a 36-volt motor system driving a 500-watt motor, which would mean 500 watts divided by 36 volts would use up to 13.88 amps of current.
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, or how many amps a battery can put out in one hour.
The battery is made up of individual cells whose chemical reactions create a flow of electrons in a circuit. Commonly found in e-bikes, these are lithium-ion cells that are put together in both series and parallel to create enough power to drive the motor at a given power output and to do so for a long enough period of time to offer good range. The battery can be attached on the outside of the frame, often either on top of the downtube or behind the saddle on a rack or integrated into the downtube.
Although the majority of e-bikes use a traditional chain drive (that connects the front chainring to the rear gears) system, there are quite a few bikes that use drive systems with a rubber belt replacing the chain. Unlike a chain that is joined by a series of links (and a master link to connect it), belt drives are made from a single loop of rubber that are favored for their quiet drive and very low maintenance.
Cargo bikes are designed, well, to carry cargo, whether it be your briefcase for work, your groceries, your camping gear or even your kids. They often have sturdy racks on the front or the rear where you can attach bags, kid seats, packages, etc. Some cargo bikes come with a large bucket in front and are made for carrying massive amounts of groceries, supplies or multiple kids.
Batteries are generally made up of multiple cells. For electric bicycles, this generally means lithium-ion batteries, and usually the size is 18650, called that because the cells are 18mm x 65mm. Some newer bikes are now using larger 21700 batteries (21mm x 70mm). Those batteries have a higher capacity, therefore offer higher potential range.
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.
Class 1 e-bike
The American e-bike classification was developed in part by PeopleForBikes to help states have a standardized way to classify e-bikes to make it easy to legalize e-bikes for various types of roads, paths and trails. Class 1 is pedal-assist only and can go up to 20 mph. Most electric mountain bikes are Class 1. As a side note, the same type of bike in Europe is limited to 25 km/h (15.5 mph).
Class 2 e-bike
Class 2 follows the same rules as Class 1, but it also has a throttle, so it can go up to 20 mph regardless of whether the rider pedals or not.
Class 3 e-bike
A Class 3 e-bike can have pedal assist at speeds up to 28 mph and can only be legally used on the street or designated bike paths. It can also be equipped with a throttle, but with throttle only, it can only go up to 20 mph.
These are electrical connections between motor, battery and controller. They often have quick-disconnect plugs to make it easy to diagnose problems with various parts of the system.
Some motor systems have apps that let you connect a smartphone app and/or control the system using your smartphone. For example, Shimano has the e-Tube app that lets you change the mode settings to add or subtract power levels in each of the different modes. Bosch also has a display designed by Cobi that allows the rider’s smartphone to customize controls and offer a bigger screen with more information than most other displays. Connectivity can not only talk to the bike, but it can help add GPS maps and other information.
This is essentially the “brain” of the bike. It connects the electronic parts of the drivetrain, including motor, battery, throttle, torque sensor and cadence sensor. It takes their inputs, plus the mode/power level you’ve selected, and pulls current from the battery to offer the right amount of pedal (or throttle) assistance to the motor.
Since the motor is running off of a battery that is DC, or direct current, the motor will also be a simple direct-current design. Alternating current, or AC, is more well-suited to power devices in the home, like lamps or televisions.
The shape of the majority of bicycle frames. It has a front triangle that is comprised of a head tube, top tube, downtube and seat tube, and attached to the rear triangle comprised of the seatstays and chainstays. The two triangles connected form a diamond shape.
Direct-Drive Hub Motor
Direct-drive hub motors are the simplest type of hub motor. The magnets are fixed on the inside surface of the hub, and the windings are permanently attached to the axle. When power is applied, the hub is made to rotate around the axle. The advantages of a direct-drive hub motor include quiet (often silent) operation, few moving parts and the ability to regenerate power into the battery (because the magnets are always moving over the coils). However, because the motor is always mechanically engaged, there is “cogging,” a drag that can be felt while coasting. Direct-drive motors must also be larger (and usually heavier) than comparable geared hub motors to achieve the same performance.
Most e-bikes have either an LCD or LED display that shows battery charge level, speed and current mode. Some offer all kinds of other information, including rider’s torque input, cadence, battery voltage and sometimes even more.
“Do it yourself.” There are kits that include a motor, battery and controller, so you can convert your traditional bicycle to electric. Others like to go the full custom route, ordering the motor, battery and controller separately. Some even build their own batteries, which is not a task for the faint of heart.
A seatpost that can go lower or higher via a remote switch that can be wired or wireless, depending on the rider’s needs. These are most often found on, or installed on, mountain bikes. They make it easy to drop the saddle when descending for better clearance, then raise it for best leg position when climbing.
E-Mountain Bike or e-MTB
An electric bike designed for off-road and trail riding. Generally, these have at least a suspension fork, but often they can also include rear suspension. Today, many are purpose-built for the specific type of riding (e.g., cross-country, downhill, enduro).
Usually, a smaller bike that can fold in half to take up even less space. Folding frames often designed with a hinge in the middle to allow the bike to fold up on itself. Frequently, the handlebars will also fold down.
A front-drive bike has the hub motor in the front wheel. This is rarely used on production e-bikes, but is quite common for conversion kits.
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.
Where early mountain bikes could also be easily identified by the big battery often mounted on the frame’s downtube, thanks to batteries getting smaller in size, many modern bikes, especially e-road bikes looking to maintain the traditional slender profile, are now mounting them internally inside the downtube.
A switch that either detects when you stop pedaling or when you actuate one of the brake levers that cuts all power to the motor, ensuring you can slow or stop as quickly as possible.
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.
Lithium Iron Phosphate
Also known as LiFePO4, this is a step up from a sealed lead-acid (SLA) battery. It offers similar performance to a lithium polymer battery but tends to be heavier.
Lithium Polymer Battery
A type of lithium-ion battery that uses a polymer electrolyte, a semi-solid gel, instead of a liquid electrolyte. These batteries provide higher specific energy than other lithium battery types and are used in applications where weight is a critical feature, like e-bikes and mobile devices. This chemistry is also the most rugged.
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 Nm, 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.
A rear-drive bike has the hub motor in the rear wheel. While there are some bikes that use a front-drive hub motor, the vast majority of production e-bikes with hub motors are rear drive.
Sometimes referred to as “regen,” it refers to direct-drive hub motors that are capable of recovering a small amount of energy back into the battery while the bike is coasting. When regeneration is active, the motor’s power is cut and its drag on the wheel increases markedly.
S-pedelec is a European term for what Americans call a Class 3 e-bike, which gives pedal assistance up to 28 mph (45 km/h).
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.
Unlike the diamond frame, the step-through frame has either no top tube, or the top tube slopes downward and often parallel to the downtube to make mounting the bike easier. You step through the bike instead of the need to swing your leg over the seat.
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.
On bikes with suspension (usually a suspension fork and often with a rear shock), it’s the amount of distance the fork or shock will move up or down to absorb bumps or hard landings. Longer travel isn’t always better, as longer-travel forks (like 150-180mm on enduro bikes) have to be beefier, therefore heavier, to handle the leverage on them, so there’s less bump-induced steering. Many commuter bikes will have a suspension fork that can travel 60–100mm to take up bumps at the front of the bike.
A device, generally on or by the right grip on the handlebar, that controls motor power. It can be incorporated into the grip or be a lever next to the grip. The more you turn the grip or press the lever, the more power you get. These are considered a Class 2 e-bike in the U.S. and are legally limited to 20 mph maximum.
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.
Tubeless tires/wheels have become all the rage for off-road riding, and as the name implies, there is no rubber inner tube to fill with air to keep the tire inflated. Instead, a specially designed rim/tire combo creates its own air chamber that stays inflated with the aid of a liquid sealant as a superior means to ward off flat tires.
The parts you use to control the power and modes of your bike. This can include a display, a touch pad, throttle/pedal assist and sometimes even a smartphone app.
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).