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The top 3 fastest cars will be automatically entered to race at the District Pinewood Derby, the Pack will pay any registration fees on your behalf. If you go to Districts, your car will have to pass inspection the day of that race again, so be advised. The track usually has two to six lanes and slopes down to the ground, since the cars are powered by gravity. Tracks may be owned by the pack or rented. The race is run in heats, giving every car the chance to run on each lane. The racers can be grouped with others from the same rank (Tiger Cubs, Wolf Cubs, Bear Cubs, etc.), or can compete against the pack as a whole.
The first, second, and third place winners usually receive ribbons, medals or trophies. Some packs also award on the basis of car design. The 1st, 2nd and 3rd place winners get to advance to the district level, then each of the district-wide race winners get to race each other from across the entire council.
The pinewood derby is a racing event for Cub Scouts in the Boy Scouts of America. Cub Scouts, with the help of parents, build their own cars from wood, usually from kits containing a block of pine, plastic wheels and metal axles. With the popularity of the pinewood derby, other organizations have developed similar events, and a small industry has developed to provide tracks, timers, scales and other products. Similar Cub Scouting events include the raingutter regatta with boats and the space derby using rubber band powered rockets.
The track usually has two to six lanes and slopes down to the ground, since the cars are powered by gravity. Tracks may be owned by the pack or rented. The race is run in heats, giving every car the chance to run on each lane. The racers can be grouped with others from the same rank (Tiger Cubs, Wolf Cubs, Bear Cubs, etc.), or can compete against the pack as a whole.
The first, second, and third place winners usually receive ribbons, medals or trophies. Some packs also award on the basis of car design. The first three place winners race winners get to advance to the district level, then each of the district-wide race winners get to race each other from across the entire council.
The forces affecting a pinewood derby car are gravity and inertia, the opposing forces are friction and air drag. Therefore, car modifications are aimed at maximizing the potential energy in the car design and minimizing the air drag and the friction that occurs when the wheel spins on the axle, contacts the axle head or car body, or contacts the track guide rail. Friction due to air drag is a minor, although not insignificant, factor. The wheel tread can be sanded or turned on a lathe and the inner surface of the hub can be tapered to minimize the contact area between the hub and body. Polishing the wheel, especially the inner hub, with a plastic polish can also reduce friction. Often one front wheel is raised slightly so that it does not contact the track and add to the rolling resistance. Axles are filed or turned on a lathe to remove the burr and crimp marks and polished smooth. More extensive modifications involve tapering the axle head and cutting a notch to minimize the wheel-to-axle contact area. Note that packs can establish additional rules for what, if any, modifications are allowed. In some areas, no changes can be made to the axles or wheels.
A second consideration is the rotational energy stored in the wheels. The pinewood derby car converts gravitational potential energy into translational kinetic energy (speed) plus rotational energy. Heavier wheels have a greater moment of inertia and their spinning takes away energy that would otherwise contribute to the speed of the car. A standard wheel has a mass of 3.6 g, but this can be reduced to as little as 1 g by removing material from the inside of the wheel. A raised wheel can reduce the rotational energy up to one-quarter, but this advantage is less with a bumpy track.
Another consideration is the track itself. A track that is mostly sloped, with little flat at the end, can really allow cars with minimal mass in their wheels to shine. However, a track with a steep slope and then a long flat section can penalize such cars due to the quick loss of energy they experience once they have reached the bottom, when all potential energy has been transferred to kinetic and rotational energy. Such cars will take a lead on the downslope, but may be passed by cars with more energy "stored" away as rotational energy on the flat.
A proper lubricant, typically graphite powder, is essential. Wheel alignment is important both to minimize wheel contact with the axle head and body as well as to limit the contact between the wheels and guide rail as the car travels down the track.