Ebike Components

Class 2? Hub or mid drive? Torque sensors? Battery size?

Buying an ebike? Confused by the choices of components and designs? This guide explains the different parts of an ebike and factors to consider to decide which options are right for you.

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Pedal Assist vs Throttle

  • Pedal-assist (or pedelec) means the bike detects when you press on a pedal and quickly provide the motor power to help. Most e-bikes allow you to dial up more assistance to go faster or provide more help for a hill climb or headwind, or dial down less assistance when you want to make the battery last longer or want to get more exercise.

  • Throttle: a twist grip, trigger lever or button that starts the motor without pedaling. An increasing number of bikes offer both - the pedal assist for normal riding and a throttle to help out when you want to accelerate fast from a stop at a busy intersection or with a big load. A throttle is useful if you have an impediment that makes pedaling physically hard for you. Of course using a throttle alone will use more electricity than using both pedals and motor. Using a throttle will also put more wear on the gears and chain.

All e-bikes can be pedaled without the motor when you run out of battery or just don't want or need the assistance. 

 

Class 1, 2 or 3?

In the United States, many states & the ebike industry define e-bikes using a three-class system, defined largely by the type of electric motor control - pedal assist only (class 1) or including a throttle (class 2) and top assisted speed of 20 mph (class 1 & 2) or 28 mph (class 3). Read our Ebike class page to learn more about the class system and how it defines what you can and can't do on your ebike.

 

The Controller: Fuel gauge & assistance levels

The controller on an ebike is a device mounted on the handlebars that controls the level of assistance from the motor. It also serves as the bike’s “dashboard,” communicating important information including the speed, amount of battery remaining, and miles ridden.

Make sure that it provides an estimate of the miles until the battery runs out of power - the electric version of a fuel gauge. 

Typically there are at least three or four assistance levels. Some models offer many more. The assistance level may be indicated by numbers with higher numbers indicating more assistance or the levels may have names like “Eco” and “Sport.” Using different modes allows you to increase range by using a lower power assistance level, or help you overcome big hills or headwinds (and make the bike feel more sporty and powerful) by using a higher power assistance level.

Check out the different levels on a test ride. Some users (particularly with cadence sensors, see below) have complained that their ebike doesn't have low enough assistance to allow them to pedal comfortably (or efficiently) at slower speeds with assistance.

 

Pedal assist sensors: Cadence vs Torque

  • Cadence Sensor - This type of sensor detects when the crank is rotating from your pedaling and turns the motor on. There will be a short delay between when you start pedaling and when the motor kicks in - typically two to three pushes on the pedal - then a surge of power. This takes a little getting used to and can feel counterintuitive at times. Starting on a hill or when heavily loaded will still take a hard push on the pedals for a stroke or two. Because of this, many ebike with cadence sensors also include a throttle so you can call on a short burst of power until the pedaling is easier.  A cadence sensor is the simplest and cheapest option for manufacturers and is typically used on lower priced models.  

  • Torque Sensor - This type of sensor measures how hard you are pressing on the pedal and provides a proportional amount of power to what you are producing. A torque sensor starts the motor virtually instantaneously and more smoothly than a cadence sensor. There is less of a surge or jolt. The harder you pedal, the harder the motor pushes. This makes the bike’s motor power feel like a natural extension of your muscle power. It also saves battery power allowing you to go farther on a charge. Torque sensors are more expensive and so typically are not used on lower cost bikes.

In many cadence sensor bikes, the assistance level that you set on your handlebar controller directly controls the speed. The higher the assistance level, the faster the speed. In most torque sensor bikes, the assistance level determines how much power the motor will add to your pedaling effort regardless of speed (e.g., adding 25% more power to your push at the lowest assistance level and 300% at the highest level). Some e-bikes use a combination of torque and cadence sensors to adjust power based both on your pedal pressure and speed and rate of pedaling.

If your riding is mostly flat and lightly loaded, cadence sensors with a throttle will probably be fine. If you ride in hills or with heavier loads, a torque sensor may make for a more satisfying ride. It is best to try out an e-bike on typical terrain before you buy.

 

Front or back hub motor, or Mid drive?

  • Hub motor- The motor is integrated into either the front or rear wheel hub. Most rear hub systems include pedal assist, but some front hub systems are limited to throttle only. Manufacturers are developing more pedal assist systems for front hub motors.

    • Pros - Hub drives are generally cheaper than mid drive and usually require less maintenance. Since the motor works directly on the wheel, it does not put any additional strain on the chain and gears of the bike, reducing wear. 

    • Cons - Hub motors usually only have a single gear so are not as effective for hill climbing. The weight of the motor placed in a wheel can make the bike feel oddly balanced and make handling harder while riding. Front hub motors, particularly, make the steering more sluggish. The heavier weight on the front or back of the bike may make picking up the bike more difficult when hauling the bike over a curb or up a stair. Removing the wheel is more complicated, making it harder to change tubes and tires.

  • Mid drive - The motor is in the center of the bike, usually integrated into the pedals.

    • Pros - It uses the bike’s gear system so can provide more power for hill climbing and acceleration from a stop. It usually weighs less than a hub motor, and having the extra e-bike weight in the middle makes it better balanced and easier to lift the bike when needed. Mid drive motors often give a smoother, more intuitive and responsive feel to the ride by using torque sensors, rather than cadence sensors.  Mid drive motors increase stability by having a lower and more central center of gravity.

    • Cons -  Mid drive motor bikes often cost more. They put more strain on your chains and gears, wearing them out faster, though companies are now producing e-bike drivetrains that can handle this better. They are more complex and so require more maintenance and have more parts to fail.

 

Motor Power: Amps vs Watts

Watts are a measure of the power that a motor is rated to provide. Most e-bikes sold for commuter or on road recreation in the US have motors rated between 250 watts and the 750 watt limit for Class I & II e-bikes. How much power you need will depend on how much weight you will be carrying and how much steep hill climbing you will be doing. Motors also have a voltage rating. Higher voltage motors generally have more acceleration power. A 24 volt 250 watt motor may be plenty for a solo commuter in flat lands and gentle hills, while a cargo bike expected to carry kids and groceries up steep hills may have a 48 volt motor rated at the maximum allowable 750 watts. 

 

Unfortunately there is lots of variability in how the watt rating is measured by different manufacturers and in other design variables that affect how much power you will experience. Therefore the rated watts are not necessarily very informative. It is a good idea to test ride a couple of bikes with different power levels to find one that’s right for you, particularly if you will be riding in very hilly territory or with heavy loads.

 

Battery Capacity & Range

Battery capacity is generally measured in amp hours or watt hours (amp hours times voltage).

A standard 24 or 36 Volt 10 amp hour battery pack will go anywhere from 20-40 miles on a charge depending on many factors including speed, weight carried, hills, wind, road surface, tire pressure, bike condition, and how hard the rider pedals and how much assistance is used.

Extended range batteries with higher amp hour or watt hour ratings may provide a range of 50-80 miles and beyond on a charge. Some models allow you to double (or even triple!) up your batteries for greatly increased range. If you plan on riding long distances between charging (50 miles or more) consider getting a second battery to bring along on those long rides).

 

Battery location: Down tube vs Back rack

  • Down tube mount: Many e-bikes put the battery on the down tube - the tube that runs diagonally from the handlebars to the pedals. Some even integrate the battery inside an oversized downtube to hide it. A down tube mount puts the weight in the center of the bike and relatively low which generally improves handling. It also simplifies wiring to a mid drive motor. This location may, however, get in the way of brackets to carry water bottles or locks. 

 
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Charging your Battery

Charging batteries generally takes 2-6 hours depending on the battery size and how far it was discharged. Charging is done with a small home charger that plugs into a normal home electric socket and normally costs less than a penny a mile in electric costs. Batteries in many models are easily removed to bring to the charger.

If the battery is integral to the frame and not easily removed by the user, consider how you will get the bike and charger close to an outlet or how you will bring an extension cord to the bike.

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  • Rack Mount: Rear rack battery mounting may work better with step through frames or where the downtube space is needed for other mountings. It does, however, put the battery weight higher on the bike which can affect handling on corners. Furthermore, having the battery on a rack is generally less secure than being built into the frame. Make sure that the battery rack still allows panniers (paired baskets on the bike’s sides) to be clipped to the side of the rack for carrying groceries or other cargo.

Wherever your battery is located, if it is removable, make sure it locks securely to the frame with a key, unless you plan on removing it when you need to lock the bike outdoors for an extended amount of time.

Protecting your bike from theft

E-bike manufacturers are starting to pay more attention to protecting e-bikes from theft. If you will be riding in high theft areas in big cities or around college campuses, their are a number of security measure to look for or to add to your bike to keep if from being stolen or stripped of valuable parts.

Make sure the battery is securely lockable. You won’t want to carry it with you everywhere.

Consider locking skewers (the bolt that holds the wheels and axles to the bike) and seatpost locks.

Some brands are starting to add security features, such as GPS trackers (e.g., Faraday), tamper detection and remote lockdown modes and retrieval services (e.g. VanMoof). GPS trackers are also available as aftermarket add ons.

And of course, do not leave the bike store without the strongest lock they sell.

For more info on locks, GPS trackers and more, see the Security section of the Owners Guide