Abstract

If you ride a bike, you probably know that you have to occasionally pump up the tires to keep them fully inflated. Over a long period of time, the tires slowly leak air, so their pressure will decrease. Have you ever noticed that it is actually harder to ride a bike when the tire pressure is too low? This is because the tires are a big factor in the rolling resistance of the bike. In this sports science project, you will measure how tire pressure affects the force required to move a bike. How important is it to keep your tires fully inflated?

Objective

Use a spring scale to measure how tire pressure affects the force required to pull a bike in a straight line.

Introduction

Riding a bike is good exercise, and can be hard work! When you ride a bike, there are many different forces you must overcome in order to move the bike forward. There is always friction between moving parts of the bike, like the gears, chain, and wheel hubs. If you are pedaling up a hill, you must work against your own weight, plus the weight of the bike. Air resistance—the collective force that results from pushing millions and millions of air molecules out of the way when you move forward—also works to slow you down. Figure 1, below, shows where all these different forces act on a bike.

What about the fourth force shown in Figure 1; what is rolling resistance? At first, you might guess that rolling resistance is just another type of friction, between tires and the ground, but this is actually not true. Bike tires are made of rubber, which is a soft material. When the soft tires come in contact with the hard ground, they deform slightly (Figure 2, below). Some energy is lost when the tire deforms and then bounces back to its original shape. Rolling resistance is the result of this energy loss as a tire continuously rolls along.

Now, can you imagine how tire pressure could affect rolling resistance? In this sports science project, you will do your own experiment to find out! You will use a spring scale, which measures force in newtons (N), to pull a bike along. You will change the tire pressure and measure how this changes the force required to pull the bike. Do you think it will require a larger force to pull a bike with under-inflated tires, or will under-inflated tires not make much difference?

Terms and Concepts

• Force
• Friction
• Weight
• Air resistance
• Energy
• Rolling resistance
• Tire pressure
• Spring scale
• Newtons (N)

Questions

• What forces must you overcome in order to move forward when you pedal a bike?
• How do these forces change in different conditions?
  • For example, does air resistance change depending on how fast you are going?
  • Can weight make it harder or easier to ride a bike, depending on whether you are going uphill or downhill?
• What causes rolling resistance?
• If a tire deforms more, is more energy lost?
• Would a fully inflated tire deform more or less than an under-inflated tire?

Materials and Equipment

• Bike with training wheels
  • Note: Due to the very low speeds when testing this science project, it is very difficult to balance a bike that does not have training wheels. It may be possible to do the science project if you have a third volunteer walking alongside the bike to keep it upright, but it is highly recommended that you use a bike with training wheels.
  • The bike should be relatively clean and well-oiled before you start the experiment. See the Procedure for details.
• Volunteer to ride the bike
  • Note: Rolling resistance increases as more weight is placed on the bike. The rolling resistance on a bike without a rider is very low, so it is very difficult to measure. So, for this science project, you need a volunteer to sit on the bike while you tow it along with the spring scale. This makes rolling resistance easier to measure.
• 50 newton spring scale; available from Amazon.com
• Large zip ties (3); available at a hardware store or from Amazon.com
• Bike pump with pressure gauge; available at a sporting goods store or from Amazon.com
• Open, flat area with a hard surface (asphalt or concrete) where you can pull the bike. A playground or long driveway will work well. Do not do this science project in a street or parking lot where there may be cars. It is very important to do the science project on a flat surface and not on a hill.
• Bicycle helmet for your volunteer
• Lab notebook

Experimental Procedure

Variations

Careers

If you like this project, you might enjoy exploring these related careers:

Related Links

• Science Fair Project Guide
• Other Ideas Like This
• Sports Science Project Ideas
• Mechanical Engineering Project Ideas
• My Favorites

Cite This Page

General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

APA Style