Racecar Tires:
How Do They Lose Air?
There are lots of different elements that go into maintaining a racecar. On race day there is a whole team of people, often known as the pit crew, that are responsible for making sure the car is performing as well as possible. There are people to check the fuel and oil, people to make sure the car isn’t running too hot, and people who oversee the tires. Racing tires are not meant to last very long, driving on them at such high speeds at such hot temperatures causes the tires to weaken so they must be replaced frequently. Part of tire maintenance is checking the tire pressure.
Air is a gas; a gas is defined as a substance that has no fixed shape and will fill whatever container it is in. Gases will expand or contract (grow or shrink) depending on the temperature of the gas, as it gets warmer the gas will expand more, as it gets colder, it will contract. In a racecar the temperature of the tire will affect the air pressure, as the tire gets hotter from being driven on for so long the air inside will expand and it forces the rubber of the tire to stretch. When the tire cools down so does the air, contracting and shrinking the tire. This expansion and contraction can stretch a tire out and eventually make it no longer safe to drive on. If the tire pressure is too high the tire won’t get any traction, it won’t stick to the track properly. If the tire pressure is too low the tire won’t rotate correctly and prevents the car from going fast enough.
Most racecar tires are not just filled with air, they are also filled with nitrogen. Nitrogen is more stable than air, meaning it is less affected by the temperature. However, for this activity we are going to see how different temperatures affect air pressure.
Materials:
Balloons (at least 6)
Soft/fabric tape measure OR piece of ribbon and a ruler
Permanent marker
Heat source (a sunny window, or a lamp that gets warm)
Cold source (fridge or freezer, make sure to permission before moving any food out of the way!)
Optional: room thermometer
Instructions:
1. Blow up three balloons until they are approximately the same size – use the tape measure to measure the circumference by going around the widest part of the balloon and draw a circle around the balloon but DO NOT connect it, leave a small gap between the two end of the line, this is be important later. Record the circumference for each balloon.
2. Place the first balloon somewhere that isn’t too hot or too cold, avoid the sunlight. This is going to be the control balloon; we are going to compare the other two balloons to this one later. If you have a thermometer record the temperature of this spot.
3. Place the second balloon in the warm spot, either a sunny window, or under a lamp (careful not to put it too close to the lamp or the balloon might pop!) (PHOTO). If you have a thermometer record the temperature of this spot.
4. Place the third balloon in the cold spot, and if possible, record the temperature of this area as well.
5. After about 20-30 minutes return to the balloons and observe any changes. Did they get bigger or colder? Did the space between the two ends of the lines get bigger or smaller? Remeasure the circumference of each balloon and record. Is there any difference from the original measurements?
Notice the red balloon (left) that we placed under the heat source expanded 1” and the blue balloon (right) that we placed in the cold source contracted by ½”.
6. Repeat steps 1-5 with 3 new balloons and use different places for hot and cold sources.
How did the heat and cold affect the size of the balloons? Think about how tires would equally be affected as the temperature of the air inside them changes as well. If the air in the tire was constantly expanding and contracting, how might that affect the rubber of the tire.