Fishman, Piercy 1

Analysis of Analysis of Naturalistic Electric Bike

Rider Behavior: Energy and Power Considerations

Noelani Fishman, West High School; Breanna Piercy, Hardin Valley Academy

Kwaku Boakye, Dr. Shashi Nambisan, Dr. Chris Cherry

Abstract

Electric bikes (e-bikes) were developed to provide hybrid human/electrical power to help

propel riders. Studies determining how much power is exerted by riders of e-bikes are

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limited. This study attempts to quantify and compare the overall energy-use of riders of e-

bikes and regular bicycles using fundamental physics relationship with real-world data. Data

from naturalistic bicycling behaviors of two riders (one with e-bike and the other with regular

bike) were obtained using GPS devices. Analysis of the data showed that the e-bike rider, on

average, exerted about half the power used by the rider of the regular bike. This project

compared the energy output of regular bikes versus electric bicycles.

I. INTRODUCTION

In foreign countries such as China or some parts of Europe, a need has arisen for a cheaper

and more efficient mode of transportation that allows consumers to travel through city streets with

ease. In the past, motorcycles and traditional bikes have curbed a large portion of this demand. In

recent times, however, e-bikes have also begun to compete with regular bikes and motorcycles in

foreign markets where the demand for this type of vehicle is high. This sudden boom in e-bike

consumerism has led to a need for more and more innovative electric bikes. Research in how to

create cheaper models, more efficient batteries, and other such improvements could allow e-bikes to

become more widespread in the world market. This study is a step in this process of bringing e-

bikes to a global stage. By defining the energy efficiency of e-bikes, this study has paved the way to

future studies that can be done in this field. This will eventually bring the world to a more energy

efficient transportation environment.

II. LITERATURE REVIEW

In 2012, the University of Tennessee hosted the United States’s first e-bike share program

known as UT’s cycleUshare. It lasted for one year consisted of a fleet of 14 bikes split between two

stations that could be found at separate locations on campus. One of these stations was completely

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solar powered. As it was a research project, the bikes could be accessed for up to 4 hours at a time

for free. This was done in order to collect naturalistic data from the bikers. Unlike the more recent

study that is explained in this paper, this previous project had a wider variety of bikers and bikes

from which to gather data. Furthermore, the newer study takes the older one a step further by

comparing e-bikes to traditional bikes.

In this study, an e-bike from UT’s cycleUshare program was used to collect the data. This

type of bike is called a pedal assist bike. This is one of the four types of e-bikes available.There are

four classes, listed here in order from Class 1 to Class 4: pedal assist, throttle on demand, speed

pedelic, moped or motorcycle. A pedal assist e-bike has an electric drive system activated only

through pedaling and can only has a limited amount of speed it can assist the rider with. A torque

sensor on the bike measures pedal movement, pedal torque, or bike speed, sometimes a combination

of two or three. The speed of the bike’s electric drive system is generally limited to twenty miles

per hour in America, and around fifteen miles an hour in Europe. The electric drive system of a

throttle on demand e-bike is activated by some type of throttle on the bike. The speed of this bike in

America is limited to 20 miles per hour while in Europe it is limited to 15 miles per hours. A speed

pedelic e-bike is similar to Class 2 e-bikes except that it reaches higher speeds. In America, this

Class is often combined with the second class while in Europe is does not have the same rights as

regular bikes and requires a license. In both America and Europe, it may be restricted to driving on

roads and private property at no greater speed than 28 miles per hour. When an e-bike is considered

a moped or a motorcycle, that means that it goes too fast and the motor wattage is too high for it to

be considered a bike under the federal or state law. While all of these classes of e-bikes seem very

different, there is one thing that they all have in common. Every e-bike has three main components:

the battery, motor, and controller. The battery of an e-bicycle is usually a lead battery, often

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referred to as a Sealed Lead Acid (SLA) battery. Due to the battery’s bulkiness, weight, lifespan,

and maintenance, companies are looking for alternative battery options. The newest technologies in

store for the batteries used on e-bicycles are Ion, Polymer, Manganese, and others. These all have

life spans that are two to three times one of a lead acid battery. In this study, a Lithium battery is

used that has 240 watts of power.

The motor is also a very important component of an electric bicycle as it adds the most

weight, ultimately slowing down the bike. Typically, the motor is from 200 W to 1000 W. The limit

in the United States is 750 W, or it is considered a motorbike. The higher rating the motor is the

more weight it can pull with greater ease but the faster it draining the battery. The most common

type of motor for electric bikes is hub motors. Hub motors are generally incorporated into the

wheels of the bike. This motor pulls or pushes the bike but at the expense that it loses efficiency on

varied terrains.

Lastly, the controller is the final component that makes an electric bicycle an electric bicycle

The two types of controllers are the pedal-activated controller and the throttle based controller. The

pedal-activated controller allows the rider adjust the level of assistance which ranges from no assist

to full assist. The second type of controller works with throttle mechanism, twisting or gripping.

The modes of operation available to an e-bike are the pedal only, pedal assist, and electric only.

Below is a graphic illustrating the locations of the aforementioned components on the e-bike used

in this study.

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III. METHODS

Throughout the process of discovering the energy exerted by both the regular bike rider and

electrical bike rider, there were many steps and equations that were needed in order to properly

analyze the data. For the first step in this project, research was done analyzing previous projects.

This developed knowledge of e-bikes and why they were not widely used throughout the United

States but were more frequently used as an alternate mode of transportation in places like China and

the Netherlands. The research also provided knowledge concerning how an electric bicycle

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operates. The research was extensive, which ultimately assisted in the later parts of the project.

Since the goal of the project was to determine the energy exerted by an e-bike rider in

comparison to a rider of a regular bike, it was decided that one subject would ride an electric

bicycle with the assistance of the electric motor while the other would ride a traditional bike. The

subjects then rode their designated bikes along the Greenways surrounding the UT campus.

Different paths were travelled each day. Above is an example of one the routes travelled during the

data collection process. Data were collected for 1-2 hours each on four days. Both bike riders rode

brought handheld GPS devices that collected the naturalistic data. This means that the devices

collected data that was derived from the riders while they were acting like they normally would.

The GPS devices were linked with a software program called GoldenCheeta, a program that

analyzes data from devices such as the ones that were used in this project. This program measure

factors such as speed, cadence (revolutions per minute), altitude, longitude/latitude, the route which

the subjects took, and other related subjects. Each day after a ride during the data collection period,

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the data from the devices was extracted and downloaded onto GoldenCheeta. After all the data had

been collected, the raw data was transferred to Microsoft Office Excel where it was applied to the

below equations in order to find the variable “W”, or power.

W=V[Kₐ(V+Vw)²+mg(S+Cr)] …..eq. 1

Cr=0.005{1+2.1/P[1+(V/29)²]} …...eq.

where W = Power, Kₐ = Aerodynamic drag factor (kg/m), V = Speed relative to ground (m/s),

Vw = Headwind velocity (m/s), m = Rider + bicycle mass (kg), g = Acceleration due to gravity,

S = Slope of hill ( % Grade) , Cr = Rolling resistance coefficient, P = tire pressure

The second equation’s purpose was to determine Cr since the rolling resistance coefficient

was unknown. The rolling resistance equation took into consideration the tire pressure and other

variables. With these equations, more raw data was determined. Below is a representation of some

of that raw data.

In

the

raw

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data, the power exertion has already been calculated. After this step, the results from the data were

organized into the table that can be seen below.

Electric Bicycle Data

Day Total Power

Average Power

Total Cadence

Average Cadence

Day 1 86343.21 25.85 93639 23.04

Day 2 163982.89 44.65 73527 14.68

Day 3 123033.15 38.08 70130 16.03

Day 4 193112.30 35.99 120142 19.80

Regular Bicycle Data

Day Total Power

Average Power

Total Cadence

Average Cadence

Day 1 88250.19 25.20 65237 16.08

Day 2 140632.76 32.38 29707 5.29

Day 3 146862.76 39.33 31166 7.11

Day 4 249191.93 44.27 65793 10.46

As demonstrated by the above data, the cadence and the power for the electrical bicycle are

greater. This is because the electrical assistance provided by the e-bike motor made the bike easier

to pedal. For example, if an e-biker and a regular biker go up a hill, then the e-biker would have an

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easier time pedaling and a higher cadence than a regular biker. Although these rates may be higher

for the electrical bicycle rider, the regular bicycle rider had a higher ratio of power per cadence in

comparison the e-bike rider. This means that the regular bike rider exerted more manual power than

the e-bike rider, where the e-bike rider made up the power with the electrical assistance.

IV. RESULTS

Once the power exerted by each rider was divided by the cadence of each rider, the manual power

exerted by each rider was determined. As shown in the graph below, the rider of the traditional

bicycle had more manual power output than the rider of the electrical bicycle. The electrical bike

rider yielded about half as much power per cadence than the regular bicycle rider.

Different types of variables could have affected the results. For example, weight of the rider

and bicycle, exercise level of the rider, exhaustion, temperature, and other factors. Some of the

main factors that affect the results of this study are the different types of resistance. There are three

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main types of resistance related to bicycle riding. The first type is aerodynamic resistance, and this

is the amount of power it takes for the bike to push forward against the wind. Another type of

resistance is Rolling resistance, otherwise known as friction. This is the amount of power the

bicycle needs to actually move against the ground. Lastly, there is slope resistance, which is the

resistance created by going uphill or on difficult terrain. All of these are factors that may have

altered the results, and because this data is naturalistic, it is prone to variables such as these.

Also, there was analyzation of the correlation of data between speed, altitude, and

cadence. The speed and cadence followed the same trend. This is because as one pedals more

generally the faster they become. These numbers were farther apart for the electric bicycle. When

the altitude was in a constant flat area, the cadence and speed increased. However, when altitude

increased in hills or slopes, the speed and cadence increased for this as well.

V. DISCUSSION

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The results resolve as was predicted in previous projects. The results quantify the amount

that electric bicycles exert more power than a traditional bike. Other projects have been done

centered around the fact that e-bike riders exert less manual power. However, no one has ever put it

into numbers the amount of manual power the electrical bicycle rider actually puts into the ride

compared to the manual power of a regular bicycle rider. They show that with electric bicycles one

can travel faster and farther with more ease than a regular bicycle. The overall point of this project

was to quantify how much less manual power electric bicycles use than traditional bicycles. This

project completed the study previously completed by Professor Cherry. The research will be a

gateway to other types of research.

The use of this project is to encourage the use of electrical bicycles. Hopefully, in the future,

Americans will realize how energy efficient electrical bicycles are. With these results, there is no

room for doubt that electric bicycles are easier for travelling use. Although some may still prefer

traditional bicycles for recreational use and traveling longer distances, such as travelling to work or

other places in a city, electric bicycles might be a better alternative. When vehicles like this are

introduced, humanity is one step closer to creating more energy efficient societies.

Research could be extended from what has already been done. For example, in this project,

the amount of electrical energy output from the battery was never measured. This could be done

through determining the charge of the battery in Watts before the bike ride and then after the bike

ride. This would show the total energy expenditure of the electric bike’s battery. This can be

predicted to be the difference between the regular bike rider’s manual power and the electrical bike

rider’s manual power. If the electrical bike rider’s manual power (e) was subtracted by the regular

bike rider’s manual power (b), it would be an estimate to the electrical assistance (ea).

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b - e = ea

The battery for the e-bike continues to be a center of study to improve this mode of transportation.

Likewise, studies also need to be done to make electrical bikes more marketable in the

United States. To do this, electrical bikes will need to become cheaper. As of now, electric bikes

can cost thousands of dollars. The battery is the most expensive component of an electric bicycle.

Since many of these batteries are made from materials such as lithium and lead, research

concerning a new battery that would be less expensive could be done. Also, battery charging and

overall efficiency need to be better as well as the weight of the electric bicycle. Many steps still

need to be taken into this field of study. This research is only a gateway into the future of electric

bicycle studies.

VI. CONCLUSION

The future of e-bike research is bright. This study acts as a segway to future areas of

research on this subject in terms of bike efficiency. This in turn could help to pave the way for e-

bikes to become a more popular mode of green transportation in the future. This being said, it is

important to note that e-bikes must be improved upon before they can this stage. Projects such as

the previous one conducted by Dr. Chris Cherry and the one that this paper concerns not only add to

the research surrounding e-bikes, but they also create awareness of the benefits of e-bikes and their

uses. By raising awareness of e-bikes, this project pushes for a future that includes yet another form

of green transportation that will work to preserve our environment.

VII. ACKNOWLEDGEMENTS

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This work was supported in part by the Engineering Research Center Program of the

National Science Foundation and the Department of Energy under NSF Award Number EEC-

1041877 and the CURENT Industry Partnership Program.

Other major contributers to this work were Kwaku Boakye, Dr. Shashi Nambisan, and Dr. Chris

Cherry. All of these people helped to guide this research in the right direction.

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