Abstract

Objective

The goal of this project is to design and do experiments that demonstrate which skateboard wheels are best for speed and maneuverability.

Introduction

The fast moving, slip-sliding sport of skateboarding looks like pure fun, but it's also an activity chock full of science. Those rotating wheels speeding along smooth cement parks or clicking across bumpy sidewalks follow the same laws of friction and rotational momentum as the classic incline plane and trolley in a physics lab. The glide you enjoy after initial push off on your board demonstrates, at least briefly, the constant speed or velocity from inertia, and the slow roll to a stop indicates that frictional forces have finally robbed you of your forward motion. Skateboarding, that high flying sport of athletic anarchists, blends balance, speed, and spunk with real life, in-your-face demonstrations of force, motion, and frictional drag.

Click here to watch a video of this investigation, produced by DragonflyTV and presented by pbskidsgo.org

This project focuses on testing skateboard wheels. The video highlights two skateboarders, Chuck and Jake, who decided to take the scientific approach to investigate the importance of wheel size to their ride. They knew that large wheels are supposed to be faster than smaller wheels, according to seasoned skateboarders and skateboard manufacturers. So they put the theory to the test. They set up two experiments to compare large wheels (60 mm diameter) to small wheels (50 mm diameter) in speed and maneuverability. Check out the video to see their results. Then read on to see how you can test their theory in a set of experiments of your own.

Jake and Chuck's approach and experimental design were definitely on target. They changed only one variable (wheel diameter) to run their experiments while keeping other variables like track distance, board size, rider weight, and skill level constant. They carefully clocked their times to tenths of a second. Still, the results surprisingly showed no difference between the large and small wheels in speed down the flat and only a slight difference in ability to successfully turn through a short obstacle course. Wheel size alone wasn't enough to make a measureable difference, at least in their experiments. If you were to repeat theses experiments would you get different results using your board, local terrain, and different sets of wheels?

The challenge of this project is to design experiments that can verify the advertised speed and performance differences between skateboard wheels. The results don't have to be huge; tenths of a second may be enough. But the differences have to be consistent and large enough to be detectable in your experiments. It's all about wheel choice and surface selection in this project.

For starters, why not set up longer test runs than they showed in the video so that there's more distance to travel and time to pick up possible differences in speed or performance of the wheels. When selecting the wheels for your tests, consider not just size but other factors that determine speed, grip and maneuverability. For example, the "hardness" of a wheel, its width, and the shape of the wheel's edge (rounded, beveled, or straight) all contribute to how fast a skateboarder can cruise, fly vertically, or turn sharply. The type of surface you skate on is another variable since soft wheels give a smooth but slower ride over bumpy terrain while hard wheels take on slick runs with greater speed but a rougher ride. Your task is to study these variables and come up with the best wheel choices to get the most "extreme" results with your board in your chosen terrain.

Modern day skateboards have come a long way from the homemade clunky contraptions of metal skate wheels nailed to the bottom of a short 2 x 4 board. The wheels, in particular, illustrate the synergy of space-age products with the development of an entire sport centered around flips, turns, verticals and the desire for speed and a sense of flight. Skateboard wheels have morphed into synthetic, highly engineered structures made from resilient, lightweight and durable plastics that encase sleek metal ball bearings to provide the smoothest and fastest spin. These designs have come about to large degree from manufacturing engineers applying a solid understanding of the physics of wheels and rotational motion.

Plastic materials, like the polyurethanes used in skateboard wheels today, are slicker than metal so they decrease the frictional forces between the wheel and the surface. This translates into both a smoother ride and increased speed per push. The relative hardness or softness of the plastic wheels also creates subtle but important differences in how the wheels roll. Generally, hard wheels mean greater speed, while softer wheels travel more slowly because they interact more with the tiny bumps in the road as you move along. As the young boarders in the video suggested, the diameter of a skateboard wheel affects speed as well. A larger wheel rotates over a longer surface distance per revolution than a smaller wheel, so larger wheels produce more speed per push, if all other factors are equal.

Which combination of wheel characteristics do you think will show the most dramatic differences in speed and maneuverability on your board? Should you use large, soft wheels with a square edge and run those against small, hard wheels with a round edge? Or should you use some other combinations of wheels? How will the wheels you select for the flat course hold up in a slalom test of turning ability? Will the slower wheels in the straight away actually turn out to be better in the rapid turns of the timed slalom course or the hard, slow turns of a maneuverability test? Can you explain your wheel choices and their eventual results based on the science of the friction and rotational motion?

To find out, start by doing some background research on skateboard wheels and the basic physics that describes their spin and speed. We've listed some suggested search terms and basic questions in the next section. Organize what you learn or know about skateboard wheel performance according to diameter, hardness, width, and shape using the summary table below. That should help keep the basic details straight and make your choices of which wheels to test in your experiments a little easier. Then bolt those wheels to your trucks, hop on your board, and run your experiments to find out if your scientific instincts are as awesome as your skateboarding skills!

Skateboard Wheels Performance Summary
Wheels	Effect on Speed	Effect on Grip	Effect on Turns
I. Diameter (mm)
Large Wheels (60+)		N/A	N/A
Medium Wheels (56-60)		N/A	N/A
Small Wheels (52-55)		N/A	N/A
II. Hardness (A)
Hard (97-105)			N/A
Medium (94-96)			N/A
Soft (85-93)			N/A
III. Width
Wide
Narrow
IV. Edges
Square
Beveled
Round

Terms, Concepts, and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• Skateboard wheels
• Friction (rolling friction and static friction)
• Velocity
• Acceleration
• Momentum
• Rotational motion
• Newton's First Law of Motion (inertia)
• Newton's Second Law of Motion (Force = mass × acceleration)

Questions

• How is friction important in the push off and in the rolling speed of a skateboard wheel? How do large wheels differ from small wheels in surface frictional forces?
• Explain how Newton's first law of motion applies to skateboarding.
• Describe how large, hard wheels perform differently than small, soft wheels. Describe the advantages of using large, soft wheels versus small, hard wheels.
• Describe how the width of a skateboard wheel affects the grip and slide of a skateboard.
• Describe how the edge shape of a skateboard wheel can affect the ride of a board and what a skater can do on the board.
• What is polyurethane? Why is it an excellent material for skateboard wheels?

Bibliography

• All the basics about skateboard wheels:
  Staff, 2007. "All about wheels," Lush Skateboard site [accessed July 8, 2007] http://www.lushlongboards.com/workshop-about-wheels-c-199_249.html?p=shop&pearlUser=ubjnsgte059759ef9ng42rf770.
• Good basic info on skateboard wheels, size, and hardness properties:
  Staff, 2007. "Skateboard Wheels," 360 Stake website [accessed July 8, 2007] http://www.360skate.com/skateboard_wheels_information.cfm.
• General information about all skateboard parts and characteristics:
  Staff, 2007. "Skateboard Help Guide," Industrial Rideshop website [accessed July 8, 2007 http://www.industrialrideshop.com/IRS/staticpopup.aspx?content=static_SkateTechTips.
• Very "rad" on line exhibit describing the science of skateboarding:
  Wanner, N., "The science and art of skateboard design," Exploratorium Museum [accessed July 6, 2007] http://www.exploratorium.edu/skateboarding/skatedesign.html, part of the larger website exhibit, "Skateboard Science," found at http://www.exploratorium.edu/skateboarding/.
• Helpful and reader friendly site introducing the physics of skateboarding:
  Robertson, B., 2004. "The Physics of Skateboarding Concepts," [accessed July 10, 2007] http://www.drskateboard.com/curriculum/physics_concepts.htm.
• Short description of the physics of in-line skating that also applies to skateboarding:
  Staff, 2006. "In-line Skating," Newton's Apple website, Twin Cities Public Television [accessed July 1, 2007] http://www.reachoutmichigan.org/funexperiments/agesubject/lessons/newton/inline.html.
• The idea for this project came from this DragonflyTV podcast:
  TPT, 2006. "Skateboard by Chuck and Jake," DragonflyTV, Twin Cities Public Television [accessed July 7, 2007] http://pbskids.org/dragonflytv/show/skateboarding.html.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

• An assistant to help you time your runs
• A skateboard park or open paved area; you will need at least 40-50 meters for the speed run
• Your skateboard
• Two sets of skateboard wheels; one set selected for fast runs, and one set selected for slow runs
• Tools to remove and attach skateboard wheels to your board
• Stop watch or timer that registers to one-tenth of a second
• Ten or more empty plastic soda bottles for the slalom course
• Measuring tape to mark off meters
• Chalk or tape to indicate the start and finish lines
• Notebook or paper
• Pen or pencil
• Helmet

Experimental Procedure

1. Select and purchase the two types of skateboard wheels you think will show the greatest difference in speed and maneuverability. Also keep in mind the type of surface you plan to use for your speed test and for the slalom course.
2. Let your assistant know the day, time, and place of your experiment.
3. Set up the start and finish lines for your speed test. Use a straight course without bumps. To enhance the opportunity to detect measurable differences between your sets of wheels, use a long test run (at least 40 meters, or approximately 131 feet) to increase the time of each run.
4. Complete three experiments for each type of skateboard wheels:
   • Experiment 1: Speed test of 40—50 meters
   • Experiment 2: Speed test on a 40—50 meters slalom course with plastic soda bottles
   • Experiment 3: Untimed turning test for maneuverability on the 40—50 meters slalom course with plastic soda bottles
5. Have the assistant stand to the side of the finish line so he/she will have a clear view when you cross it. The assistance should shout "start" to get you going, and push the stop watch to begin timing.
6. For each experiment, make at least ten runs. Then switch the skateboard wheels and repeat the experiment.
7. Note: If you think you will be getting tired before the end of an experiment, make five runs with one set of wheels, change the wheels, and make five run with the second set of wheels. Repeat the same testing sequence once more to obtain a total of ten runs per wheel set. Alternatively, you can separate the experiments into two or three days, but be sure to test both types of wheels each day.
8. Skate the speed runs as fast as you safely can. Your assistant should record the total time it takes you to travel the distance and cross the finish line. In the slalom speed test, travel as quickly as you can while carving tightly between the bottles. If you knock over more than two bottles, that run should not count. In the slalom maneuverability test, you are not timed. The goal is to go slowly and carve widely so that you don't knock over the soda bottles. Record the number of bottles that do get knocked over in each run.

Analyzing Your Data

1. Total the seconds for Experiment 1 and also for Experiment 2; calculate the average time for each experiment.
2. Total the number of bottles knocked over in Experiment 3, and calculate an average number of "knock overs."
3. Make a bar chart showing the average results for the three experiments. Show the data from the two types of wheels side by side under the three experimental categories.
4. What were the differences in average times, if any, between the two different wheels in Experiment 1 and Experiment 2? Were the results consistent between the two experiments?
5. Did you detect any difference in maneuverability between the two different wheels in Experiment 3?
6. Did your results match your predictions about which type of wheel was best for each experiment?
7. Were you surprised at your results? Why or why not?
8. For help with data analysis and setting up tables, see Data Analysis & Graphs.
9. For a guide on how to summarize your results and write conclusions based on your data, see Conclusions.

Variations

• Another skateboarder. Would a different skater produce similar results with your two types of wheels? Try using a person of different size and weight. How does Newton's Second Law (F=ma) apply when you compare these results to your first set of experiments?
• Repeat with other wheels. If you don't see any differences in these experiments, what other combination of wheels could you try to test to detect a difference in speed or maneuverability?
• More tests. What other variations or types of experiments could you design to test your wheels? Would you get similar results if you tested the wheels on a smoother or rougher surface? How about a different spot at a skate park?
• Physics of skateboard tricks. Research and explain the physics involved in doing an "ollie" and a "kickflip." What forces push the boarder and the board up, sustain both in the air, cause rotations of the board, and bring both back to the ground at the same time?

• For more science project ideas in this area of science, see Sports Science Project Ideas.

Credits

Darlene E. Jenkins, Ph.D.

Sources

The idea for this project came from this DragonflyTV podcast:

• TPT, 2006. "Skateboard by Chuck and Jake," Twin Cities Public Television http://pbskids.org/dragonflytv/show/skateboarding.html.

Last edit date: 2008-06-17 00:00:00