How To Improve A
Pinewood Derby Racing Car

Brian D.

The building and racing of a pinewood derby car can be a very difficult process. "The goal is to have the car move from starting line to finish line in the least amount of time possible"1 (Stan Pope, 1997). Gravity is the main power source moving the car along the track. One formula that applies is force equals mass times acceleration, or F=ma. Gravity pulls on an object at a rate of 32 feet per second per second. Gravity moves the car on the slope of the track, and ceases to move the car on the flat of the track. There are two forces; those pushing the car along the track, and those pushing the car into the track. These two forces are components of the car's gravity force vector. Friction is the main force acting against the car. Friction is therefore the main cause of energy loss. Motion in spite of energy [friction?] is released in the form of heat. This process happens when the car's wheels roll on the rack, slide on the track, and rub against the guide rail. These are the main physical forces acting upon the Pinewood Derby car.

Methods have been created in order to improve the Pinewood Derby car. Before the car races lubricants such as graphite can be applied to the car. One idea is to lubricate the wheels and axles by putting them in a bag with graphite a few days before the race. Oil shouldn't be used because it would collect dust and other materials, and slow the rate of speed of the car down. In an normal Pinewood Derby the cars should be lubricated right before the race, and are not allowed to be lubricated after the car is inspected and impounded. Improvements to the car's body should not shorten the car. The axles should be placed as far to the front and rear of the car as possible.

Aerodynamics concerns are important, but should not be taken into very serious consideration. Aerodynamic improvements generally do not apply to a pinewood derby car for a few reasons. One is that the car is not moving at a significant rate of speed. Another is that the car is too small to be affected by drag. And finally, The car is traveling too short of a distance. Sometimes an unmodified block of wood can win if it has the proper adjustments to weight and wheels.

There are other facts about the Pinewood Derby that are important. The actual body is 7 inches long by 2.75 inches wide. The length of the track is 32 feet long, and 28 feet from start to finish. A track can have anywhere from 2 to 8 lanes that are 0.250 inches thick by 1.625 inches wide. The start of the track is usually 4 feet higher than the flat of the track. The profile slopes from 30 degrees to 0 degrees about 12 feet from starting line. The above mentioned dimensions are measurements most commonly used, but there are several variations. Most races are judged by either human judges or an electronic judge, such as "The Judge". This system is made by a company called New Directions. This system includes software to measure times down to 1/100 of a second. It also announces places and has other various functions for controlling a Pinewood Derby. The normal race setup for "the Judge" system can include a over-the-track unit that contains telephone-type chord, a small computer, and a power source (usually batteries). The system determines winners by using small lasers directly over each lane. This system is similar to simple home protection system involving lasers and mirrors. When an object passes between the laser and the mirror on the track, such as a pinewood derby car, the information is sent back to a computer connected to the unit. A device on the starting line assures all cars are started at the same time. While "The Judge" is reletively new, there have been devices similar to it for almost 10 years.

Rules for the Pinewood Derby's are extremely simple, but are often broken by the competitors and overlooked by the race judges. "When the official kit arrived, our team examined the rules closely, keeping an eye out for loopholes of the type that would lead the team to victory."6 (Frank Markus, P.107) One sort of unwritten rule is that is the cub scout's race, not their father's and that the cub scout should participate in the building of the car as much as possible, with as little help from his father as necessary. Actual rules include restrictions on weight, length, and wheels. In most places the total weight of the car must be under five ounces. All bodies must be original Boy Scout's of America or BSA stock. The car does not have to have a definite front or back. The car must use gravity as it's only power source. The car's racer must be present at the race. When an electronic judge is used to determine results there are some additional rules. The car cannot have anything that would fool the sensor at the end of the track. The car may not have anything that goes past the starting device. "These rules are checked at an inspection before the race, and are then impounded before the race starts."2 (Unknown author, website)

There are additional rules especially for the wheels and axles of the car. The wheels and axles must be original BSA stock, but do not have to be from the kit itself. Competitors are allowed to purchase BSA kits with only wheels and axles. The wheels may not be shortened in width. The axles may not be connected. At least one wheel of the car must be on the track at all times. "Sometimes some kits are better than others."3 (no author, website) Kits can sometimes come with major flaws that the competitor doesn't realize until race-day.

The Pinewood Derby has a very long history. It originated sometime around the 1950's. Another event similar to the Pinewood Derby is the Shape N' Race Derby. This derby takes is part of the Christian Service brigade. Other awards besides those based on speed can include most original, most humorous, most grotesque, most mouth-watering (similar to classic car era), weirdest looking, and a variety of others. Most of the time a Pinewood Derby is divided by rank, including Tiger Cub, Wolf, Bear, and Webelos. Top competitors from the pack ( usually about one pack per school or church) will be able to compete at district, council, and possibly higher levels. In most areas the scout's age is between 7 and 10. Sometimes a pack will hold another derby just for the parents. This is a way the parents can be competitive and exhaust their creative outlets."5 (Randy Worcester, website) All of this information varies from pack to pack due to size and other qualifications.

Mass location or where to add more weight is a very controversial subject. Since Gravity is the main power source, the more weight one can add onto the car the better because of forces pulling down on the car. Some people say put the weight in the center of the car, others say put 60 percent in the rear, 40 percent in the front. One of the most used ideas is to put the weight in the rear and slightly to the one side so that only 3 out of the 4 wheels are touching the track. Other people say to completely center all the weight. New ideas develop every race. A research study from the University of Michigan engineering school shows that pouring molten lead into the wheels themselves has the best results. This school had used several different ideas when it did it's research. Of course, the average kid, or even the average father does not know how to use molten lead. One more idea is to put .38 caliber bullets in the car.

When using normal weights from the BSA, people usually put them on the top of the car, where they are more easily accessed, or in the bottom of the car. Weights from the BSA are small bars or round circles. At district and council levels almost all cars are exactly 5.0 ounces. Another way of reducing friction between the track and the car is to have the car's axles angled 5-10 degrees down so only the inner part of the wheel touches the track. Most competitors focus the most attention on the reduction of friction and put aside the shape and aerodynamic values of the car, and simply stick with a wedge or flat design.

Improvements on the wheels are possibly the most important improvement on the car. The nails or axles of the cars must be de-burred and polished. The wheels can also be polished. The best way to do this is by using emery cloth and a drill. One idea is to lubricate the wheels and axles by putting them in a bag with graphite. Wheel alignment is also an important issue. If the wheels are not properly aligned, then the car will rub against the guide rail creating friction, and thereby slowing the car. "A properly aligned car can travel almost 8-10 feet on the ground."7 (Eric Burgess, interview)

Different energies are affecting the race car while on the track. The amount of energy equals the mass times height, or E=mh. This formula describes how fast the car will move. When the car is actually on the track and moving it has kinetic energy. When the car is sitting on top of the track and not moving it has potential energy. When the starting device is activated the potential energy transforms into kinetic energy.

There is a fairly basic procedure for making the car. First, the Cub Scout makes a design on piece of tracing paper or directly onto the car with a pencil. "Flat, wedge-shaped, or round designs usually win the races."4 (Jay Silvan, Grand Prix Pinewood Derby page.) Then, the car is cut out using a small saw, and for minor details, a pocketknife. If weights are to be used on the bottom of the car they are put on now. The car then gets a paint job of primer and paint. Wheels are adjusted in the ways previously said, and then added to the car. After this is complete the Cub Scout can add finishing touches, such as decals.

Race day procedure is as follows. The car is registered and inspected by judges and then impounded. In most cases cars are first raced by den. After that car's are raced by rank. Depending upon the size of the pack, winners from races by rank will race other people in the pack, or move onto district races. After these races are done, competitions for other characteristics are begun. Finally, at the end trophies and prizes are handed out. Usually awards are given to the top three winners of each rank, but this may differ according to the size of the Pack or participation.

As has been pointed out in the preceding paper, the Pinewood Derby can involve advanced scientific ideas and principles. Friction is perhaps the most important are to be concerned with. Wheels are the most perfected area of the car. Also the Pinewood Derby has had a long history that is continually updated. What is thought to be simply a race for young children using wooden blocks, really has applications for advanced science and technology. Physical science is a key factor in the design and racing of Pinewood Derby cars.

Standard Version of Racing Track

Standard Version of Racing Track

Reference List

  1. Pope, Stan "Pinewood Derby Car Design." 9/18/97
  2. Unknown Author "Pinewood Derby Website" 10/1/97
  3. Unknown Author "Ultimate Pinewood Derby Page" 10/11/97 (appears to be a dead link)
  4. Silvan, Jay "Grand Prix Pinewood Derby Page." 10/15/97
  5. Worcester, Randy "No Title." 10/18/97
  6. Markus, Frank (1995, March). Day of Thunder, Sort of. Car and Driver Magazine. pp.107-109
  7. Burgess, Eric (1997, October, 17). Buffalo Grove, IL Dennen House. (Interview)

At the time he wrote this paper in November, 1997, Brian D. was a first class scout in Troop 79 of Long Grove of the North East Illinois Council. He was in the 7th grade and was 13 years old. In his troop he acted as Quartermaster and occasionally ASPL. He has been in the scouting program since the 3rd grade.

Now, March, 2000, Brian is 15 years old, a freshman at Stevenson High School in Lincolnshire, IL. He is a brotherhood member of the Order of the Arrow, a counselor at Ma-Ka-Ja-Wan Scout Reservation, and senior patrol leader of his troop.

Original: 11/15/97. Latest update: 3/17/2000
Copyright 1997 © by Brian D. All rights reserved.
Printed here by permission of the author.