Jack and Jill Went Up a Hill and Came Biking Down After: Choosing the Best Gear Ratio for Speed
AbstractAre you a budding Marianne Vos or Greg LeMond? Are you into cycling and speed? Then this is the science fair project for you! In this science fair project, you will determine the best gear ratio for your bike, to get the highest speed after a curve and onto a straightaway. You will learn a lot about applied mechanics and gears, all while having fun riding your bike.
Michelle Maranowski, PhD, Science Buddies
- This project is based on the following DragonflyTV episode: TPT. (2006). Kart Racing by Ali and Paige. DragonflyTV, Twin Cities Public Television. Retrieved November 21, 2008.
To determine which gear ratio setting on a bicycle will result in the highest speed.
One of the first bicycles built was called a penny-farthing bicycle. It had a huge front wheel with pedals connected to it, and a smaller back wheel. In order to make the bicycle worthwhile to ride, the front wheel had to have a large diameter. Unfortunately, the issue with this design was that it was unsafe to ride.
Figure 1. An example of a penny-farthing bicycle. (Wikipedia, 2008.)
At the turn of the century, the penny-farthing bicycles were being replaced by the safety bicycle. The safety bicycle had two wheels of equivalent size. The design of the bicycle has not changed, in terms of essential parts, from that time until now. The bicycle is made of the following parts: the frame, a seat, the handlebars, two wheels of equivalent size, the brakes, the crank and pedal, and the chain and the gears.
The set of gears connected through a crank to the pedals is called the chain wheel and the set of gears connected to the rear wheel is called the free wheel. (You can see additional bicycle parts labeled in Figure 2, below.) The idea behind multiple gears is to allow the cyclist to change the distance the bicycle moves forward with each rotation of the pedal. For example, a low gear means the pedals rotate much faster than the wheels, making it easier to climb up hills. A high gear is the opposite, allowing the wheels to rotate more quickly than the pedals, which enables better cycling down hills. The distance that the bicycle moves forward depends upon the ratio between the chain wheel and the free wheel gears. To learn and understand how to calculate the gear ratio, refer to the Science Buddies science fair project Gears Go Round. You can calculate the gear ratio by counting how many teeth each gear has and dividing the number of teeth on the chain wheel by the number of teeth on the free wheel.
Cyclists adjust the gear ratio according to how fast they want to move, the type of path they are on, and the conditions of the path. Watch the DragonflyTV video to learn how two kart racers, Ali and Paige, investigate how gear ratio affects racing speed. Once you have watched the video, it will be your turn to apply what you saw! Find a good bike path on which to experiment with the gears and gear ratio of your bicycle. Remember to wear all of your safety gear, especially a helmet, during this science fair project.
A bicycles frame is made of a top tube, down tube, seat tube, seat stay and chain stay. The seat set is made of a seat and a seat post. The front set has a handlebar grip, head tube, shock sbsorbers, front brakes and fork. Each wheel has spokes, hub, rim, cover and valve. The pedal is attached to a crank arm which connects to a gear and drive chain. There are also a front and rear derailleur and a cassette and rear brakes on the back wheel.
Figure 2. This diagram shows the components of a standard bicycle. (Wikipedia, 2008.)
Terms and Concepts
- Gear ratio
- What is a gear?
- Where are other places, besides bicycles, that gears are used?
- Wikipedia Contributors. (2009, January 5). Penny-farthing. Wikipedia: The Free Encyclopedia. Retrieved January 5, 2009.
- TPT. (2006). Kart Racing by Ali and Paige. DragonflyTV, Twin Cities Public Television. Retrieved November 21, 2008.
The following website describes the parts of a bicycle and how bicycles work:
- Brain, M. (2000, April 1). How Bicycles Work. Retrieved November 21, 2008.
This website gives a good tutorial on gears:
- Brain, M. (2000, April 1). How Gear Ratios Work. Retrieved November 21, 2008.
Materials and Equipment
- Access to a bike path
- Multi-gear bicycle
- Bicycle speedometer or bicycle computer; both available online at Amazon.com
- Adult volunteer
- Bicycle helmet and safety gear
- Lab notebook
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- To start this science fair project, you should become familiar with the bicycle that you are using. You should know how and when to change the gear ratio.
- Open the speedometer package. Read the operating instructions and learn how to mount it onto your bicycle. Test the speedometer or bicycle computer to see if it is accurate. Ride your bike a known distance and see if the reading you get is that distance. Do this a couple of times to make sure that you are getting accurate readings.
- Find an appropriate bike path on which to do your testing.
- You want to make sure that there aren't a lot of people around, so you may have to do your testing at a time when the path is least likely to be busy, such as at daybreak. Have an adult volunteer accompany you to the bike path.
- Do not perform this experiment at sunset or in the dark.
- The path should have a curve, followed by a straightaway.
- The path should be long enough that you can see a difference when you test. Ride the path a few times to make sure that it takes 30–40 seconds to ride, and to familiarize yourself with the path.
- Note down in your lab notebook what the path is made of and the conditions of the path. For example, is the path rocky or slippery? These are the kinds of conditions that affect speed.
- Start the testing. Put on all of the safety gear, especially the helmet. Find a comfortable pedaling rate. Try 60 rotations per minute (RPM). If this is too slow, then increase it until you find a level with which you are comfortable. Make sure that you are not pedaling so fast that you spin out on the curve. It's very important that you try to stick to this pedaling rate for the entire project so your results are accurate.
- The speedometer should be cleared and ready to measure. Start at one end of the curve. Note the gear ratio in your lab notebook. Ride the path until you reach the end of the straightaway. Record the speed from the speedometer in your lab notebook.
- Repeat step 5 two additional times. Record all data in your lab notebook. Make sure you take breaks in between each trial so that you're just as energetic for each one.
- Change the gear ratio four more times and repeat steps 5–6 for each change. Try to choose gear ratios two above the original setting and two gear ratios below your original setting. Record all data in your lab notebook.
- Plot your data on a bar graph.
- How fast were you able to go? Which gear ratio proved to be the best?
Ask an Expert
- How does changing the pedaling rate affect speed and the gear ratios required?
- Try a different path. For example, if you did the original testing on a paved track, try riding on a dirt path. How does the path material affect speed and the gear ratios?
- Take a look at this other Science Buddies project if you are interested in learning more about gears: Gears-Go-Round!
If you like this project, you might enjoy exploring these related careers: