Electric bikes are the kings of versatility in the cycling world. Riders can treat them like regular bikes (albeit much heavier versions) and rely on their own physical power to move them, but they don’t have to.
The e-bike’s main claim to fame is its ability to provide variable levels of assistance to the rider. It accomplishes this using two systems: pedal assist and the throttle.
The former augments a cyclist’s own pedaling force, while the latter powers the bike forward on it’s own, no effort required. These functions are the reason for e-bikes’ skyrocketing popularity.
But, how exactly do these systems work? Through the interplay of various constantly evolving technologies, designs that are both efficient and affordable make these functions possible.
The specifics of these designs vary across brands and individual bikes, but the basic concept is the same. To best understand it, it will help to have a brief primer on e-bike mechanics.
The Components of an Electric Bike
E-bikes have all the same parts as a regular bike, with some key additions. A rechargeable battery is what makes the bike electric, and a motor is what provides the much-lauded assistance. Other components manage the power or provide necessary feedback to the rider.
All of an e-bike’s bells and whistles depend upon the power provided by the battery. Often the heaviest single component on a bike, the batteries characteristics directly influence the capabilities of powered assistance.
Battery voltage is the baseline figure that sets the limits of performance. For instance, engage the throttle on a bike with a 24v battery, and your speed will likely max out around 13-15 mph. Boost that battery to 48v, and you can see speeds from 20-25 mph.
Currently, Lithium-ion Polymer, or LiPo, batteries are the most common, found on 90% of all e-bikes. They have an ideal balance of capacity, retention, and weight, and are also easier to fit into different form factors.
This component receives the power from the battery and routes it to other parts requiring power, most importantly the motor. It is aptly named, because it can control many of the motor’s functions, such as its rotation, speed, and even torque.
The controller’s amperage rating is critical in determining an electric bike’s total power. Multiplying the battery voltage times the amps provides the wattage. In the United States, 750 watts is the maximum allowed for an e-bike, which limits max speed to roughly 25 mph.
The actual work of pedal assistance and throttle propulsion is performed by the motor. The current state-of-the-art is the brushless motor design, and it is placed on one of three spots on your bike.
Hub motors are placed either on the front or rear wheel hub and work by turning the wheel directly in response to either the pedelec system or throttle.
Front hub motors are cheaper but offer less power than the other options in general. As the rear wheel is still being influenced by the rider’s pedaling, this type of motor can create an awkward riding experience when using pedal assist.
Rear hub motors rotate the back wheel, which is a more natural method of propulsion for a bike. They provide greater torque and power, making them a better choice for e-bikes with a throttle.
“Mid-drive” motors forgo hub placement and are installed on the drivetrain instead. They provide propulsion by rotating the cranks, the same as you would while pedaling, and are the most natural-feeling option.
How Does Electric Bike Pedal Assist Work?
Of the two electrical assistance options, pedal-assist is the most prevalent, as it can function efficiently using all types of motors. How it works depends primarily upon the sensors used to engage it: speed sensors, and torque sensors.
Also known as “cadence” sensors, these devices measure the motion of your pedals. Turn on your pedal assist, and as soon as you rotate the cranks forward, the sensor will trigger the motor to engage.
Alternately, the sensor can measure the speed of the rotation, only triggering when a certain cadence has been achieved.
Pedal-assist based on this method does not adapt to the rider’s effort. When the petals begin to rotate, the motor will engage and provide a level of assistance based on a pre-set power level.
For instance, if you set the assist level to “high” in order to power up a steep incline, it will still provide that high level of assistance if you engage it on a decline or level path. The rider must remain aware of their settings. This is usually made easier by an LED display.
Torque sensors measure your pedaling force and provide power relative to how much effort you are exerting. They are usually installed in the bike’s bottom bracket, or within the motor itself.
Because this sort of pedal assist is adaptive, provides a more natural riding experience. Where the cadence method will often provide more power than you need, the torque method grants just enough.
This makes it more energy-efficient, allowing a higher range of ratings per charge. It also improves low-charge performance. All these positives don’t come without a cost, however. Torque sensor pedelecs are the costlier option.
You can manually set the power level higher to get maximum assistance at all times. However, the level of exertion required with this system provides a better workout for those still looking to sweat a little.
Pedal Assist Max Speeds
With both methods of pedal assist, there is an upper-speed limit, beyond which the bike will not assist you. On some e-bikes, particularly those rated for use in the UK, this speed is 15 mph. In the US, it’s 20.
Of course, a bike can go faster than this while unpowered, so this is not your max speed. However, once you reach this limit, pedal-assist will switch off and you’ll be traveling under your own power until your speed decreases.
Different levels of Assistance
With most pedal assist bikes you get different level of assistance offering a wider range of speed control. Some bikes go as far as providing 4-6 assistance levels.
But they can be largely classified into three major levels high, medium and low. At lower setting you still do most of the work ( 80% ) doing good workout but for longer distance or time.
From the medium level you will start to feel the effect of the assist. At this level you would feel as there is always a strong tailwind assisting you from back.
This can be a nice balance between pedal assist and your manual effort with 40% assist and 60% manual. Here you will start to gain significantly more speed for the effort.
Then on the highest level your legs are less in control and more as an additional power. You will start to feel like a superman as a little more effort will generate unexpected speed.
These can be great for riding uphill or commuting to work where speed and time is more important than having a workout. On the downside it will exhaust your battery faster so need to use it wisely.
How Does Electric Bike Throttle Work?
The throttle is the more power-hungry assist mode, and it’s no wonder why. Engaging this function causes the motor to fully take over propelling the bike.
The rider doesn’t have to pedal, they can simply flip a switch and enjoy the ride.
However, it wouldn’t be much of a long ride. The range that an e-bike can travel under various levels of assist differs from bike to bike, but a fair average is 20-100 miles. The lowest number in the range always represents how far the bike can travel using only throttle.
The throttle is best used to get up steep inclines, or to take over when a rider is exhausted and needs a brief break, or can’t see themselves pedaling that last mile home.
Using the throttle is very simple. The controls can come in different forms. There are twist throttles, thumb levers, switches, and push-button varieties. Most of these have at least a few settings, ranging from low to high. All a rider has to do is flip the switch to the setting they desire, and the throttle will take over.
Throttle Top Speeds
As with pedal assist, there are maximum throttle speeds mandated for electric bikes. The throttle cannot propel you at speeds exceeding 20 mph in the US, or 15 mph in the EU.
These speeds match the pedal-assist cut-off speeds, however, because the throttle is not paired with pedaling, you are less likely to exceed these limits (except when riding downhill).
Keep in mind that altering your throttle to exceed these limits will change your bike’s legal status.
Limits of the Law
When it comes to electric bike regulations, the rules of the road are still being written. However, the presence and performance of throttle is something that is sometimes prohibited.
In the US, e-bikes that meet the definition of Class 1 vehicles are not allowed to have a throttle at all. The same is true in the EU for L1e-B e-bikes.
On other classes of e-bikes, the throttle can be present, but there are top speed limitations. In the US, a bike that can reach speeds above 20 mph while being powered by the motor is considered an electric moped or motorcycle, even if it meets the wattage restriction of 750w for an e-bike.
Electric bikes have been around for a long time, but it is only in recent years that the technology has allowed their true potential to be unleashed.
The throttle and pedal assist functions operate smoothly, and are simple to understand.
The help they offer to riders who are overweight, injured, elderly, or disabled can’t be overstated, but they are hardly limited to any one type of rider.
Ride bikes for exercise? Set the assistance to its lowest setting, or turn it off altogether. Commuting and need an extra burst of speed to avoid being late? Hit the throttle and cruise to your destination.
Electric bikes lower the barrier to entry into the cycling hobby in a way that regular bikes simply can’t. They provide the option of assistance when you need it, and the ability to turn it off when you don’t.