8/19/2020

Electric Scooters: Range vs Weight

Advances in battery technology have led to a market filled with high-quality electric scooters for everything from tooling around the neighborhood to competitive off-road racing. It’s an exciting time to buy a scooter, but also a confusing time, given the array of brands and models on offer. Even among scooters designed mainly for commuting, specifications can vary widely and it’s hard to know exactly what the numbers mean, especially when it comes to how far your scooter can take you.

Potential buyers may only pay attention to specs related to daily use, such as top speed, weight, charging time, and range. The last number represents an estimate of how long the scooter can travel on a single charge. The Unagi Model One, for example, lists a range of 15.5 miles (25 km) for both its single-motor E250 and dual-motor E500. Some scooters will list a slightly lower range, some higher. But it’s important to understand that this is only an estimate and may not represent real world conditions.

Achieving optimal range depends on a number of variables, including scooter weight, rider weight, terrain, average speed, battery size, motor size, and motor efficiency. Electric scooter manufacturers calculate range using a few basic assumptions that may not apply to many riders, including a weight of around 165 lbs (75kg), an average cruising speed of around 12 miles per hour, little to no wind, and dry, flat terrain.

Since conditions vary so widely, advertised ranges can only provide a guideline. Below, we’ll look at some of the physics and engineering of electric scooters to help you better understand range capabilities and to get the most out of your electric scooter.

Range & Weight: The Forces of Scooter Motion

As we move on any wheeled vehicle, we’re fighting physical forces that want to slow us down. On an electric scooter, the battery, motor, and wheels are fighting those forces for us, pulling the combined weight of both rider and scooter with torque produced by the motor. Weight is a significant factor in how far a scooter can go before it runs out of charge, since the vehicle is pushing in two directions against drag, rolling resistance, and gravity.

The Force of Drag

Even on a cloudless day, drag, or wind resistance, will endeavor to make an electric scooter’s motor work harder and drain its battery faster. A number of different factors determine drag. Micromobility company Spring provides the helpful explanation of the formula below:

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Cd is the drag coefficient. How aerodynamic you are. Unfortunately, your body isn't designed to slice through the air. While a Tesla has a drag coefficient of 0.24, a human has a drag coefficient of ~ 1.

A is frontal area. You experience more drag the bigger you are. If you are 6 feet tall, you have more surface area running into the wind than someone shorter. Crouch down in a squat and you'll speed up.

v is velocity. The velocity term is squared. That means if you are going twice as fast, your drag will be four times as strong. To get the most range out of your scooter, you'll zoom down the bike lane at 3-4 miles per hour.

ρ is the air density. This is constant around the Earth. If you managed to ride a scooter at the bottom of the ocean, there would be a lot of drag. On the other hand, you won't experience any drag on the surface of the moon.

Increased drag from a combination of these variables results in decreased range since it requires more power from the scooter to compensate. While we cannot change some of these factors, lower average speeds will result in decreased drag and longer range.

Rolling Resistance

As you stand on a scooter, the wheels compress slightly, which increases the amount of torque required to move them. This is what is known as rolling resistance—your wheels don’t exactly want to move forward under the force of gravity. You, or rather your scooter’s motor, have to make them move (unless you’re rolling downhill). The rolling resistance of a wheel increases with the force of gravity, so the heavier a scooter and rider are, the more the wheels will fight moving smoothly. Underinflated tires, poorly designed wheels, or worn wheel bearings can also increase rolling resistance, and a higher rolling resistance means less range since the scooter’s motor has to work harder, and draw more charge from the battery, to overcome it.

range_vs_weight_02.jpg

Gravity

You’ve probably noticed that it’s harder to go up hills than go down them. We’re all intimately familiar with the force of gravity. Greater mass—which means greater rider and scooter weight—makes it even harder to get up those hills, increasing the strength of gravity that the scooter’s motor has to contend with. This means that if you live and ride in a place that has a lot of hills, your scooter’s overall range will be decreased. It also means that a lighter scooter will generally have greater range in hilly terrain and a heavier scooter will have less range.

Range & Weight: Electric Scooter Engineering

Scooter Weight

An electric scooter’s weight will be determined by a number of factors, including construction materials and battery and motor size. And, as we’ve discussed, a lighter scooter isn’t just easier to carry up and down the stairs. It can also be a factor in increased range, all other things being equal. A few high-quality scooters, like Unagi, use lighter materials that don’t sacrifice durability or build quality, such as aluminum, magnesium, and carbon fiber, the same materials used to build professional racing cycles.

Other manufacturers may rely on heavier materials, which can result in a slower scooter with decreased range. Scooters designed for off-road use or heavier riders will generally use both heavier construction materials and larger batteries and motors to counteract that added weight. Some electric scooters in this class advertise a range of 30 miles or more. They also weigh significantly more than most commuter scooters. One heavy-duty scooter, for example, comes in at 65 pounds (“one of the lightest in its class”) versus Unagi’s 23 and 26.5 pounds for its single- and dual-motor versions, respectively.

Battery Size and Age

A larger battery will hold more charge, theoretically resulting in greater range. However, larger batteries also mean additional weight, which has the opposite effect. Manufacturers must balance these two factors to find an optimal size for their scooter’s battery.

Battery capacity “is one of the important factors that determine electric scooter range,” the Electric Scooter Guide points out. Capacity is measured in watt hours (wh), which is calculated by multiplying the voltage by the ampere hours (ah), numbers that should be listed in the scooter’s specifications (or on the battery itself). A typical scooter will have “a capacity of around 250 watt-hours while monster scooters can have capacities of almost 3,000 hours.”

range_vs_weight_03.jpg

Additionally, over time, lithium-ion batteries will hold less charge. “A fully charged 1-year old scooter stores less energy than a fully charged new scooter,” notes Spring, meaning that range should reasonably be expected to decrease over time. Battery life and range will also be affected by using lights or other accessories.

range_vs_weight_04.jpg

Motor Size and Efficiency

Most commuter electric scooters have hub motors built into one or both wheels. These motors generally range from 250 to 500 watts each, which provides a very good balance of power and weight. Electric motors are usually extremely efficient and make use of a high percentage of the power they produce, though an inefficient motor can still be the cause of decreased range.

High performance scooters, on the other hand, can have much more powerful motors. The heavy-duty Wolf Warrior advertises two 1200-Watt motors for a top speed of 50 miles per hour and a range of over 40 miles. Why aren’t all scooters designed with the kind of power we find in off-road or heavy-duty scooters? Well, the Wolf Warrior weighs over 100 pounds and will not easily fold up and fit in a closet or under a desk at work.

Most people shopping for electric scooters are looking for the optimal balance of fun and utility for getting to and from work, taking a quick trip to the store, or zipping around with friends. This means most riders want a scooter that is almost as easy to carry as it is to ride. Decreased weight can come at the cost of decreased range, however, if battery capacity and motor size are compromised. The best scooter for you is one that achieves the ideal balance between all of these variables, depending on where you’re going, what the terrain will be like on the way, and how long it takes to get there.


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