Pedalling Through the History and Physics of the Bicycle

Today is world bicycle day - the celebration of this enjoyable mode of transportation extends across all ages and continents (except Antarctica). It opens up opportunities by providing a fast and easy way to get anywhere within a large radius. It is the method many people opt for to get to school or work. For example, globally over 1 billion bicycles are being used, with over 100 million being manufactured each year [1].  

The bicycle has become a staple in many cultures as the centre of competitions, or the source of cherished memories of people learning to cycle, with stabilisers, tumbles and tears. 

This day not only encourages people to get outside and go cycling, but also tries to encourage governments to improve cycling mobility, through integrating cycling into transportation infrastructure so more people can ride safely [2]. The President of the World Cycling Alliance, Raluca Fiser said:

“The main mission [of world bicycle day] is to promote cycling as a mode of transport for the benefit of people worldwide and the bicycle as a unifying, global symbol that is accessible to all.”

— Raluca Fiser, President of the World Cycling Alliance [3]

Therefore, let the celebrations begin!

Let’s Pedal Through the History of the Bicycle

The bicycle has been on a journey full of challenges over two hundred years to get to where it is today. In 1817, a German inventor named Karl Von Drais developed a two-wheeled steerable device. It was rather dissimilar to present-day bikes, as it had a heavy wooden frame (23kg), and no brakes or pedals [4, 1]. Therefore, this heavy device was hard to control and so was not extremely popular, yet Drais took his invention to England anyway. Here, an English coach maker, Denis Johnson improved its design by creating ‘hobby horses’. These consisted of larger wooden wheels, and many metal parts, but still no pedals [1]. For an image of a hobby horse from the 1820’s, click here. [5]. 

Pedals were first implemented on the front wheel in the early 1860s, yet they were quite unstable. These bikes consisted of a wooden frame, with two steel wheels and a gear system and were known as velocipedes. Then Eugène Meyer and James Starley entered the scene, they developed a bike with an oversized front wheel which gained popularity in the 1870s and 1880s. These bikes were called ‘penny-farthings’, and they led to the creation of bicycle clubs and competitive races [4].

Figure 1: James Starley: “penny-farthing” bicycle. Reprinted from Encyclopædia Britannica [6].

However, there were safety concerns due to the staggering height of the saddle (4 feet above ground level!), therefore in 1885 Englishman, John Kemp Starley, designed a bike with wheels of equal size and a chain drive. These new developments were promptly followed by other improvements in the braking system. 

In 1887, John Boyd Dunlop created the are-filled pneumatic tyre in an attempt to solve the ‘sore bottom’ his son got from riding a bicycle with solid wheels on cobbled streets [7]. They became popular in 1890 and were added to most bikes soon after this. Interest in these bikes spiked in the 1890s, causing a bike craze to follow in the USA [4]. A New York Times article from 1896 even stated that ‘the bicycle promises a splendid extension of personal power and freedom, scarcely inferior to what wings would give’ [8].

Why Are Bicycles So Fast?

Many are curious as to how a bike can reach speeds of 70km/h without having an engine, or even petrol. It is because bicycles are so efficient at converting the power our bodies produce into kinetic energy. Bikes can be up to 90% efficient, whilst electric motors are only 85% efficient, and diesel engines are a mere 40% efficient [9]. This means that a bike can convert up to 90% of the energy we supply to it through pedalling into kinetic energy, moving the bike forward. According to the Bicycling Science book by David Gordon Wilson et al: a racing cyclist at 32kmm/h could travel over 574 kilometres per litre if there were a liquid food with the energy content of gasoline! [10]

In order for a bike to accelerate, the cyclist must apply more force to the pedals, meaning the pedals move around faster, pushing the wheels around and moving the bike. The force applied must be larger than the total resistance facing the bike, meaning the total of the air resistance and the rolling resistance facing the bike. Rolling resistance is the force that opposes the motion of the tyre as it rolls around. If this criterion is met, the bike will accelerate. However, as the bike speeds up, the force of the air resistance and the rolling resistance will increase until the force applied to the bike is equal to the total resistance, the bike will then have reached its terminal velocity and will not speed up or slow down until either of these forces changes.

Why Do Bicycles Stay Upright?

Many answers have been proposed to this question, for example, some thought that bikes stayed upright due to the conservation of the angular momentum of the wheels, or because of bikes forward momentum [11]. However, these are just common misconceptions. The answer is a combination of 3 reasons, resulting in the bike’s wheels returning back underneath the centre of mass of the bike:

1. The weight of a bike’s front wheel and handlebars is usually slightly in front of the steering axis, so when the bike leans towards the left, the downward pull of this mass helps to turn the wheel to the left, placing the wheel back under the centre of mass, keeping the bike upright [12].

2. There is a gyroscopic effect from the wheels which helps steer: the wheels on a bike are spinning objects, and when you try to turn a spinning object, the object tilts as if you pushed it 90 degrees away from where you actually did. This happens vertically on a bike, so if the bike leans leftward, it makes the front wheel turn to the left, helping the wheels to return back underneath its centre of mass [12].

3. The steering axis of a bike tilts backwards (see figure 2 for reference), meaning that the front wheel touches the ground slightly behind the axis [12]. This means that when the bike leans leftward, the upward force from the ground acts to turn the handlebars and the wheels to left, ensuring that the bike’s wheels are back under the centre of mass of the bike.

All of this results in the bike staying upright, even when there isn’t a person on the bike, as long as it’s travelling forward and at the right speed. If the bike is moving too slowly it won’t turn quickly enough and will crash into the ground.

Figure 2: A diagram of a bike. Image Credit: Calfee Designs [13].

Why Celebrate?

Cycling is widely popular, especially in Denmark where 9 out of 10 of people own a bike, whilst only 4 out of 10 own a car! On average people in Copenhagen cycle 3.0 km per day [14]. It is no surprise that many people favour the bike over other transportation methods, like driving, because cycling is a fun, affordable, dependable and is an environmentally-friendly way to get to places and improve your health .

It is healthy:

The act of pedalling causes less strain than most other forms of exercise, it uses all of the major muscle groups and it improves strength and stamina. Cycling can increase your cardiovascular health, muscle strength, decrease stress levels, and decrease body fat. Some evidence even suggests that regular cycling can decrease your risk of breast cancer [15]!

A 5-year study published in the British Medical Journal, which involved over 263,450 participants with a median age of 52 detailed the benefits of cycling. The cyclists in the study had lower rates of heart disease, cancer and death. It was observed that cycling can increase peoples lifespan by up to 20 years [16]!

Therefore, there are huge health benefits involved with cycling. 

Time-saving:

Cycling is extremely time-efficient: the average walking speed is 5 km/h, whilst the average cycling speed lies between 16-19 km/h. This time adds up, meaning you can speed up your daily commute to work or school, saving you precious time in bed.

Environmentally-friendly:

Cycling is a more environmentally friendly alternative to driving. The average European car emits roughly 14 times more carbon dioxide per kilometer driven than a bike,  without even taking into account its production. A bike's emissions come from the carbon dioxide released when food, the fuel of bikes, is produced.

Producing a car requires a large amount of energy and metals that have to be extracted from their natural compounds, this therefore releases large amounts of carbon dioxide. As a result, using your bike more often would vastly improve your carbon footprint, for example, if people in the USA switched from driving cars to riding a bike for their short daily trips, between 21-45 million tonnes of carbon dioxide would not be released [14].  This would be immensely helpful in reaching the UN’s Sustainable Development Goals by 2030.

Table 1: The environmental impact in terms of carbon dioxide emissions of cars, and bikes. Information compiled from Ref [17]

Furthermore, if more people used the bicycle, there would also be less need for large parking lots, saving valuable money, and space from being used for the development of these lots [18]. 

This wonderful machine has provided many people with health, increased strength, a decreased carbon footprint, and happy memories, not to mention the money that you can save by not needing petrol or a car. John F Kennedy even said: “Nothing compares to the simple pleasure of a bike ride.”[19] It is definitely a machine worth celebrating.

How Can You Get Involved?

Get peddling!

With the COVID-19 quarantine rules still in place in many parts of the world, it is even more vital that you get at least one form of daily exercise (NB: Follow local lockdown/quarantine rules!), and the perfect way to celebrate today is by using the machine under the spotlight, the bike. You could even post your experience on social media to raise awareness.

Raise awareness:

Whilst bikes may seem very accessible, to many in need they are rare and hard to find. For instance, in rural Kenya, women can spend up to 6 hours travelling to get water per day, using up roughly a quarter of their daily energy intake. Bikes have the potential to cut this time in half and energy expenditure by at least a third [20]. This problem is rarely discussed and needs to be addressed further. 

Donate your bike!

If you have a bicycle that you do not use anymore even if it is partially broken or worn down, you can donate it to certain reuse projects. They will fix up your bike and donate them to refugees and asylum seekers or people in need [21].

Definitions

Carbon footprint - The amount of carbon dioxide released because of the activities of an individual, organisation, or community.

Kinetic energy - The energy an object has due to its motion.

Gyroscope - A device consisting of a wheel or disc mounted so that it can spin rapidly about an axis which is itself free to alter in direction. The orientation of the axis is not affected by tilting of the mounting.

References

[1] Elizabeth Palermo, Live Science. (2017). Who invented the bicycle? [Online]. Available: https://www.livescience.com/44765-who-invented-the-bicycle.html

[2] United Nations. (2018). World bicycle day [Online]. Available: https://www.un.org/en/observances/bicycle-day

[3] Word Cycling Alliance. (2019). Celebrate World Bicycle Day On 3rd June [Online]. Available: https://www.worldcyclingalliance.org/advocacy/celebrate-world-bicycle-day-on-june-3rd/

[4] Evan Andrews. (2017). Pedal Your Way Through The Bicycles Bumpy History [Online]. Available: https://www.history.com/news/pedal-your-way-through-the-bicycles-bumpy-history

[5] Museum of Bikes and Applied Sciences. Reproduction Draisine or hobby horse bicycle [Online]. Available: https://collection.maas.museum/object/207233

[6] Britannica, James Starley's “penny-farthing” bicycle, 1883. Science Museum, London, Crown copyright. [Online]. Available: https://www.britannica.com/technology/penny-farthing

[7] Tom Ambrose, The History Of Cycling in Fifty Bikes. The History Press, 2014. Available: https://www.thehistorypress.co.uk/articles/from-discomfort-to-joy-dunlop-s-pneumatic-bicycle-tyre/

[8] David Murray. (2019, December). Electric bicycles take Asia, Europe by storm. Is Montana next? [Online]. Available: https://eu.greatfallstribune.com/story/news/2019/10/23/european-countries-like-germany-italy-and-netherlands-e-bikes-now-make-up-nearly-quarter-all-bike-sa/4022117002/

[9] Chris Woodford, The Science of Bicycles. Explain that stuff, 2019 [Online]. Available: https://www.explainthatstuff.com/bicycles.html

[10] David Gordon Wilson, Theodor Schmidt, Jim Papadopoulos (contributor) Bicycling Science, 2004 [Online]. Available: https://books.google.co.uk/books?id=0JJo6DlF9iMC&redir_esc=y

[11] Matt Soniak, Balancing on a Bicycle. Mental Floss, 2010 [Online]. Available: https://www.mentalfloss.com/article/25830/why-it-so-hard-balance-bicycle-thats-not-moving-and-easy-one

[12] Minute Physics. Youtube, 2015 [Online]. Available: https://www.youtube.com/watch?v=oZAc5t2lkvo

[13] Calfee design, The Geometry Of Bike Handling, [Online]. Available:  https://calfeedesign.com/geometry-of-bike-handling/

[14] Bike Munk.  25+ Biking Statistics That Won’t Surprise You At All [Online]. Available: https://bikemunk.com/biking-statistics/

[15]  European Cyclist Federation. (2019). ECF celebrates world bicycle day [Online]. Available: https://ecf.com/news-and-events/news/ecf-celebrates-world-bicycle-day

[16] Better Health Channel. Cycling health benefits [Online]. Available: https://www.betterhealth.vic.gov.au/health/healthyliving/cycling-health-benefits

[17]  European Cyclist Federation. (2013). How much CO2 does cycling really save? [Online]. Available: https://ecf.com/news-and-events/news/how-much-co2-does-cycling-really-save

[18] Walk and Roll peel. Benefits of Cycling [Online]. Available: http://www.walkandrollpeel.ca/cycling/benefits.htm

[19] The Telegraph. (2016). 20 Quotes that capture the beauty and brutality of cycling [Online]. Available: https://www.telegraph.co.uk/health-fitness/body/20-quotes-that-capture-the-beauty-and-brutality-of-cycling/jfk/

[20] Brown education. Roles of bikes in developing countries [Online]. Available: https://www.brown.edu/Departments/Joukowsky_Institute/courses/13things/7079.html

[21] The Bike Project homepage. [Online]. Available:  https://thebikeproject.co.uk/pages/mission