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Kart Racing by Ali and Paige

We like to beat the boys on the racetrack. In fact, we call our team "Beat the Boys!" Our races are on different tracks with different conditions, so we have to adjust our karts before each race. The gears are the main thing we change. Each gear has a different number of teeth and each gear changes the way it drives. So the question is: Which gear gives us the best performance?

What did we do?
We know that we can get the best performance out of our kart when the engine is running at 6100 revolutions per minute (RPM). We get three practice runs before a race, so we tried out 3 different gears. We recorded the peak RPM for each trial from the reading on the kart's computer. We also measured lap time, since that's how you win. Our goal was a 39 second lap time. On your mark, get set, GO!

What did we find out?
The first run gave us a pretty good lap time of 41 seconds and a peak RPM of 5900. When we changed to a larger gear for round two, we improved the lap time a little and had a peak RPM of 6100. This was right on target, but we still wanted a faster lap time. So we increased the gear size for the last test. The RPM increased to 6200, but the lap time was slower. Kart racing is all about balancing trade-offs. A tiny change in a gear can totally change how something else on the kart performs. Ali raced with the middle gear setting, hit her ideal RPM and won the race!

What can you do?
  • Check out your bike's gear system. What gears do you use when you're climbing up a hill? Why? How about when you're flying down the hill? What if you want to pick up speed on a flat stretch? Find the gear settings that make your legs the most efficient. Write down what you find.
  • Make a pulley system out of sewing spools. Pound two nails into a board far enough apart so a rubber band stretches between them. Place a large spool over one of the nails and a small one over the other nail. Slip the rubber band around both spools; now, when one turns the other does too. Place a mark on the bottom edge of each spool and one on the board right next to it. Design an investigation that relates the diameter of each spool to how many times they each turn. Does the length of the rubber band make a difference?
  • Use this go kart investigation as a science fair project idea for your elementary or middle school science fair! Then tell us about it!
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