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The theory behind building the best Pinewood Derby car you can (Cub Scout motto: Do Your Best!) is to understand how the race works. The number one hurdle for any car is FRICTION! Cars are placed at the top of a hill, released, and gravity pulls the cars down the hill. The cars will accelerate until the track levels out, then gradually slow down as they approach the finish line. Throughout the entire length of the track, the car will experience friction from several different areas. With race times measured to the nearest 0.0001 second, reducing those various friction forces is what will provide faster speeds and an edge over your competitor.
What is friction?
Friction is "The resistance that one surface or object encounters when moving over another."
In simpler language, friction is the rubbing force between your hands, or in the case of the Pinewood Derby, from the wheels riding on the track and as they turn around the axel. It can even come from the shape of the car as air moves over the car's body! Lets explore how to reduce friction in these areas. Before we continue, it would be best to review the rules and regulations for the race you are entering in. Not all Pinewood Derby races have the same rules. For Pack 135, the rules can be found here.
WIND FRICTION
Imagine placing your hand out the window of a moving car on the highway. You feel the wind hitting your hand, pushing it towards the back of the car. Turn your hand into a wing, and there's less push. Make it blunt like you are shaking hands and it gets pushed, harder. This is wind friction. The car you are in has an engine powerful enough to push the car through the wind. A Pinewood Derby car does not have any engine or motor, so the wind friction will make contact with the car, slowing it down. The shape of the car will determine the amount of push-back from the wind that it will encounter. Slim and low profile cars will have less friction than those that are block shaped.
AXLE FRICTION
Pinewood Derby kits come with four (4) nails that must be used with your car. During manufacturing, the nails are stamped into their nail shape. That stamping leaves behind small burs that put friction on the wheels. And, the surface of the nail is rough. Using a small file, you can remove the burs under the nail head. Using high grit sand paper, you can polish the axle. The red areas marked in the nail photo are the defects in the nail that should be removed.
WHEEL FRICTION
Pinewood Derby kits come with four (4) plastic wheels. All four (4) wheels must be used, but not all must make contact with the track! Elevating one of the front wheels slightly will reduce the amount of friction that is attributed to the wheels' contact with the track by 25%!
LUBRICATION
Any surface to surface contact will require lubrication to reduce friction. These areas are where the wheels meet with the body and where the wheels ride on the axles. Graphite is the only lubrication permitted on pinewood derby cars.
WEIGHT AND PLACEMENT
All Pinewood Derby race rules limit the weight of a completed car to five (5) US ounces. Without getting into the physics and theory of the exact location, the bulk of the cars' weight should be located just in front of the rear axle. All cars will weigh different amounts before adding weights and adding weight is highly recommended. Any material can be used to increase the cars weight, but care should be taken to place it in a concentrated location where it will not fall off or move. Builders can use bolts, nails, pennies, etc to increase their car's weight up to the maximum. For more advanced builds, the use of tungsten can be used. By volume, tungsten is the densest metal but is also costly. Be careful with being at 5 ounces, if the official scale reads the cars as being slightly over, the removal of weight will be required before racing.
ADVANCED: RAIL RIDING
When a Pinewood Derby car races down the track, a combination of forces affect its speed. At times, the wheels will enable the car wiggle as it travels. This side to side motion reduces the speed of the car. Rail riding is when you take one of the front wheels and slightly angle it towards the center of the track's lane. When released, the car will move to one side with the wheel making contact with the track's center rail. Though this will provide a friction contact, the amount of speed lost to this contact is far less than that experienced when wiggling side to side.
ADVANCED: ALIGNMENT
A car tire has much more friction with the pavement than a bicycle tire. On a Pinewood Derby car, this also holds true. A wheel that is making full contact will have more friction than one that is making less contact. Angling the axles by a small amount will permit the wheels to ride on their edges, thus reducing the friction caused by their contact with the track.
All photos taken from TurboDerby.com. For more advanced techniques, please visit their page here. Always remember, this race is mainly for youths. We are giving them memories they will cherish, and their involvement with the build process is very important. The level of the build should compliment their abilities, not the guardian's.
As an adult, if you wish to make the fastest possible Pinewood Derby car using all the advanced techniques at your disposal, we'll meet you at the Open Race.
Last updated 01/30/2025.
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