Are Two Wheels Better Than Four?

E-Bikes and E-Scooters May Be the Next Frontier in Electric Vehicles

Image Source: InsideCreativeHouse/Stock.adobe.com

By Alex Pluemer for Mouser Electronics

Published January 5, 2023

The proliferation of electric bicycles and scooters has increased exponentially in recent years. That upward trend promises to continue as supply chain issues and inflation make gas-powered vehicles and four-wheel electric vehicles (EVs) more cost prohibitive. Many e-scooters offer the benefit of being easily collapsible and portable, making them a good option for people whose commute typically includes some form of public transportation (i.e., using the scooter to get to and from the bus station or subway stop).

E-scooters take up less space and are easier to carry and store indoors than e-bikes, which are typically much heavier than traditional bicycles (some e-bike models are collapsible but are still much heavier and more cumbersome than collapsible scooters). For longer commutes, e-bikes are likely the better option; they provide a more comfortable ride due to their larger wheels and shock-absorbing tires. They usually boast higher top-end speeds (with some exceptions) and longer ranges. E-bikes are also a good option for exercise, as users can engage the motor as much or as little as they like, which is especially useful when riding uphill or on difficult terrain.

Additionally, e-bikes (particularly models equipped with throttles) offer greater utility than e-scooters for transporting heavy materials, with some e-bikes already outfitted with front and/or rear racks or child seats. E-bikes are also a more convenient option when the battery is low or empty; riding a bike is more manageable than kick-pushing a scooter over long distances. While some e-scooters feature attached or attachable seats, most models are of the standing variety. From a cost perspective, e-scooters are typically less expensive than e-bikes at the point of purchase and require less regular maintenance.

Battery life in both e-bikes and e-scooters (measured by the total number of charge cycles) can vary significantly by model and manufacturer, which can make it difficult to determine approximately how much total “bang for your buck” you’re getting. In this article, we'll look at the technologies featured in different e-bikes and scooters and what might lie ahead for two- and three-wheel EVs in the future.

E-Bike Features and Technology

We will confine this section to examining "pedal-assist" e-bikes, which are equipped with direct current (DC) motors that engage and add power when the rider is pedaling. (E-bikes that don't require pedaling to activate the throttle aren't legally considered e-bikes in many parts of the world, including the U.S.) Many pedal-assist e-bikes include a device on the handlebars that allows the rider to adjust the power level the motor will add to the speed they're generating by pedaling, similar to changing gears on a traditional bicycle. All e-bike motors will stop assisting when the e-bike reaches a certain top-end speed, which varies depending on the e-bike's classification.

Types of e-bike motors are differentiated by their location on the bike’s frame and the way they transfer motor power to the wheels.

• Mid-drive motors are located between the pedals on the bike's frame. This position provides optimal balance and typically offers the smoothest ride while also being lighter than direct-drive or geared hub motors.
• Direct-drive (or gearless hub) motors are located on the rear wheel hub, where you’d find gears on a traditional bicycle. They utilize magnetic force rather than mechanical gears, which typically reduces maintenance time/costs. The drawback is that they're heavier than geared motors and take more time and effort to reach top speed; therefore, they are difficult to pedal uphill or when the battery is drained.
• Geared hub motors (Figure 1) are also located on the rear wheel's hub and are the most common and typically least expensive type of e-bike motor. Geared hub motors receive power directly from the battery rather than through the pedals and generally don't provide as much assistance or top-end speed as other motor types.

Figure 1: An example of a rear geared hub motor. (Source: batya/stock.adobe.com)

The level of power assistance an e-bike motor will provide is measured in watts (W) and depends on the capacity of the bike’s battery (Figure 2), measured in volts (V). Higher-voltage batteries push more power through the controller to the motor, generating higher torque and speeds. Battery voltage capacities of pedal-assist e-bikes usually range from 48V to 96V. The three most common types of e-bike batteries are lithium-ion, lead acid, and nickel hydride, although there are others.

Figure 2: Close-up of a battery on an e-bike. (Source: mmphoto/stock.adobe.com)

E-bike motor power ratings are typically differentiated in increments of 250W, ranging from 250W on the low end to 1000W at the top of the spectrum. Lower-wattage motors are generally better for commuting and recreation, whereas higher-wattage motors are better suited for transporting cargo or negotiating difficult terrain.

The amount of time an e-bike battery will last on a single charge—the battery capacity—is measured in amp hours (Ah); the higher the battery's capacity, the more amp hours it can run at a given power output. By multiplying a battery's voltage by its amp hours, you can determine how many watt-hours (Wh) the battery can supply (e.g., a 500Wh battery will run a 500W motor at full capacity for one hour or at half capacity for two hours).

Pedal-assist motors kick in only when sensors indicate the rider is pedaling. Some e-bikes utilize cadence sensors, which measure the speed at which the pedals turn. Higher-end e-bikes implement torque sensors, which measure the force the rider exerts on the pedals and indicate how much assistance the rider requires.

E-Scooter Features and Technology

E-scooters come in a wider variety of designs than e-bikes; some are built like kick scooters with attachable seats, and some come with three wheels and built-in seats. The two-wheeled type usually features hub motors attached to the wheels themselves, whereas larger scooters often implement chain-drive motors located in the scooter's deck.

Hub motors have fewer moving parts and typically require less maintenance but don't provide as much torque or top-end speed as chain-drive motors. Hub motors found in e-scooters are essentially the same as those in e-bikes, geared or gearless, with the same relative benefits and drawbacks. Hub motors in e-scooters are usually located on the front wheel below the handlebar, although some models feature dual hub motors, one motor on each wheel.

Chain-drive motors are more complex mechanisms and create more internal friction, which can lead to more wear and tear. Chain-drive motors are easier and less costly to repair, and changing out a bad wheel or tire on an e-scooter is a more straightforward process when the motor isn't attached to the wheel hub. Chain-drive motors are also more energy efficient than hub motors and are better suited for going uphill or moving heavy cargo.

Whether chain drive or hub, DC motors on E-scooters fall into one of two types: brushed or brushless. Both types use electromagnets inside and around the axle to turn the wheels. Brushed DC motors carry electric current through carbon or graphite brushes, which wear down over time and eventually need to be replaced. Brushless DC (BLDC) motors perform the same function without brushes, enabling reduced wear and tear and increasing overall efficiency. BLDC motors are also a newer technology and are featured in almost all newer e-scooter models. 

E-scooters typically offer lower motor power than e-bikes, although some models of e-scooters exceed 1200W and can reach top speeds upwards of 60mph. More typical commuter e-scooters have power levels ranging from 250W to 500W; a 250W motor will top out at around 15mph, and a 500W motor at approximately 25mph. 

Batteries in two-wheel, foldable e-scooters are typically smaller than e-bike batteries. They won't run as long on a single charge, but an e-scooter's amp hours can vary greatly depending on the type and model. As e-scooter users aren't adding to their propulsion by pedaling as they would on an e-bike, battery power will be consumed more quickly. 

The E-Bike and E-Scooter Market

The e-bike and e-scooter market is segmented in a way that makes it difficult to pin down its exact size or rate of growth. Different battery and motor types as well as e-bikes with or without throttles are either considered separate entities or all part of the same market, depending on the source. Some estimates on the size of the global e-bike and e-scooter market in 2021 range from $20–40 billion, with the market expected to grow to $100–120 billion by 2030. 

Most research agrees that the market is proliferating due to consumer preferences for more environmentally friendly and cost-effective alternatives to gas-powered vehicles, four-wheel EVs, and/or overly crowded public transportation. E-bikes and e-scooters can also reduce commute time in densely populated urban areas with heavy traffic and don't necessitate finding parking or paying parking fees.

Laws and regulations regarding e-bikes and e-scooters vary worldwide and are both helping and, in some cases, hindering their widespread adoption. More rigid global emissions standards make EVs more practical than gas-powered vehicles, and e-bikes and e-scooters are much more affordable than four-wheel EVs. 

As already noted, the U.S. has strict safety guidelines for what constitutes an e-bike: The motor power cannot exceed 750W, the top speed can be no higher than 20mph, and e-bikes with throttles are considered a different class of vehicle and are subject to different standards. Other factors slowing e-bike and e-scooter adoption are the overall lack of charging infrastructure (also a problem of four-wheel EVs) and the worldwide shortage of materials used to make lithium-ion and nickel hydride batteries. As with four-wheel EVs, engineers are putting significant research and development into new types of battery technologies. The most promising of these new technologies is the graphene battery, which uses electrolytes that increase battery capacity and reduce charging time and overall weight.

Conclusion

E-bikes and e-scooters are already competing with four-wheel EVs in urban areas and promise to be even more competitive as battery capacities grow and their ranges are extended. A significant selling point for commuters is the convenience of foldable e-scooters that aren't prohibitively heavy or burdensome. They can also be enjoyed recreationally by people of all ages, especially kids and young adults. E-bikes have similar recreational utility and are a good option for exercise, particularly for people who are new to cycling and are afraid of overextending themselves on a traditional bicycle. As fuel prices continue to rise and emission standards become more stringent, the demand for EVs of all varieties will only grow. Further development of battery technology and charging infrastructure will only boost the proliferation of e-bikes and e-scooters around the world.