How Pinewood Derby Cars Work
Pinewood derby cars are gravity-powered vehicles. They start the race on a sloped track held back by starting pins. When the pins drop, the cars roll down the sloped track towards the finish line, guided by rails. Most tracks are built with a transition from the sloped starting section to a long flat section. On these tracks, cars must complete the flat section while maintaining as much speed as possible.
The only force that can be used to make the car move is gravity. But since gravity is a constant there is nothing you can do to get more! Fortunately, there are things you can do to get the most from this constant force.
While our ally, gravity, pulls the car down the sloped track, our enemy, friction, is hard at work slowing down the car. In every place where moving parts are in contact (wheels rubbing on the track, the axles, the car body, and the guide rails) friction is at work. Even the air flow over the car body is a form of friction that slows down the car.
A final factor that must be considered is momentum. In an automobile, momentum helps the car keep rolling when you take your foot off the gas. In a similar way, momentum helps a pinewood derby car to continue rolling as fast as possible on the flat section of the track.
So, to build a fast pinewood derby car you must maximize momentum and minimize friction. How is that done? Keep reading to find out how.
The 5 Keys to Pinewood Derby Performance
Champion car builders have discovered many secrets for getting the most speed from a car. However, there are 5 Keys to pinewood derby performance. Whether or not you learn all of the extra little tricks, careful application of these 5 Keys will guarantee that you will have a competitive car.
Key 1 - Maximize Momentum
As stated earlier, momentum must be maximized for top performance; and the key to momentum is weight. In each race, there is a maximum allowable weight for the car (usually 5 ounces, but certainly check your local rules). Momentum is maximized when your car has the:
Maximum allowable weight for your race
For a five ounce maximum weight, you will likely need to add 2 or 3 ounces of weight to the car. But where on the car do you add the weight?
Add weight towards the rear of the car
Tests show that best performance is achieved on most tracks when the weight is added towards the rear of the car. This can be overdone, but a simple test to make sure the car is properly weighted is to balance the finished car on a COG Stand. The car should balance about 1 inch in front of the rear axle.
Does the type of weight matter? The maximum weight can be achieved with any type of weight; however, the type of weight does affect how easily the desired weight can be achieved. Denser weights (such as Lead or Tungsten) take up less space, so it is easier to reach the maximum weight. Also, since denser weights require a smaller volume of space, they allow creation of more aerodynamic cars (which is Key number 2).
By the way, if you are in a BSA-sponsored race, ignore the picture on the front of the BSA kit. Use the slot closest to the end of the block as the rear axle (see Figure 1).
Key 2 - Aerodynamic Shape
There are many elaborate ways to improve aerodynamics, but to simplify matters, let's use the following principles:
- Low-profile cars (smaller surface area as viewed from the front of the car) will tend to outperform higher-profile cars.
- Cars should taper from a smaller surface area in the front to a (possibly) larger surface area in the rear.
- Edges running across the car should be rounded or tapered.
- Wings, sails, flags, pennants, etc. add to the surface area, thus they tend to decrease performance.
To add some balance to this topic, Key 2 (aerodynamics) is not as important as the other 4 Keys, so I don't suggest that you sacrifice looks to achieve an aerodynamic shape. So, if you want to build a car that is not particularly aerodynamic, don't worry about it. Just make sure that the other 4 Keys are carefully followed.
Key 3 - Wheel & Axle Preparation
All of the frictional losses in a pinewood derby car come from the wheels and axles. Start by inspecting the parts in your kit to make sure they are usable. If a part has a serious flaw, replace it.
Next, prepare the nails.
- Place the nail in the chuck of a drill and use a Mini-File to remove the flashing under the nail head and minimize the ridges on the shaft. Beveling the nail head slightly is also a good idea.
- Optionally use the Pro-Axle Press to ensure that the nails are straight and round.
- Finally, polish the axles with an Axle Polishing Kit until they are bright and shiny.
To prepare the wheels, use a Pro-Wheel Mandrel and some wet, fine grit sandpaper to polish the wheels. If allowed by your local rules (and the configuration of your wheels), use the Pro-Hub Tool to cone the inside wheel hubs.
Key 4 - Lubrication
Lubrication is an extremely important key. The difference in time between a well-lubricated car and a car without lubrication can be one-half second or more (this translates into several feet on the track).
Most people use graphite for lubrication. Graphite is carbon that has been ground up into a fine powder. There are many varieties and qualities of graphite available at hobby and hardware stores, so make sure to get a good brand. We offer Max-V-Lube Graphite, which has been proven to produce top results in pinewood derby racing.
When lubricating with graphite, take the time to work it in thoroughly; a casual puff before the race is not sufficient. Before mounting the wheels and axles on the car, spend five minutes per wheel adding graphite, spinning the wheel on the axle, adding graphite, spinning the wheel on the axle, etc. Always end by spinning.
After lubricating, make one or two test runs to break in the lubricant (or free spin the wheels several times). Since graphite works best after a break-in period, don't re-lubricate between race heats.
Key 5 - Alignment
In order for the car to get to the finish line as quickly as possible, it needs to go straight. If it zigzags down the track, it will travel a longer distance, but worse it will continually lose speed as it bumps and rubs against the guide rail.
To minimize the amount of alignment adjustment needed, make sure that the axle slots/holes are perfectly parallel to each other and the axles are straight. Also, when using axle slots, make sure that the axles are inserted perfectly straight. The Pro-Axle Press and the Pro-Body Tool are great tools to help minimize the need to align the wheels. In addition, the Pro-Axle Guide will help you insert the wheels and axles properly.
There are a few different alignment procedures, but the simplest method is as follows:
- Determine which of the front axles appears to be the most firmly on the ground (or with a raised wheel, adjust the wheel/axle that is on the ground).
- Remove the axle from the car and remove the wheel.
- Use the Pro-Axle Press and Pro-Rail Rider Tool to put a slight bend in the axle.
- Replace the wheel and re-insert the axle with the bend downwards.
- Roll the car on a smooth and level surface.
- If it does not roll straight, slightly rotate the bent axle by grasping the axle head with a pair of pliers.
- Repeat steps 6 and 7 until the car rolls straight.
- An alternate alignment method is known as "Rail-Riding". For more information on this technique, Click Here.
Are the 5 Keys not enough for you? You want to know all the tricks and secrets to fast pinewood derby cars? Then you need "Speed to the Finish", the most complete pinewood derby manual available to today.
Let's make this simple. To achieve Key 1 and Key 2 can take some trial and error. But you only get one chance a year to test out a design! What do you do?
If you would like to eliminate the trial and error, thus maximizing your chance of a trophy win and maximizing the value of your time then consider our Car Plan Booklets. Each booklet has step-by-step instructions and full-scale templates for three winning designs. These plans implement Keys 1 and 2, so you don't have to worry about them.
Click here for More Information
Short on time or woodworking tools? Our Pre-Cut Car Kits are made from our winning designs, and they implement Keys 1 and 2. They are pre-shaped for aerodynamics and pre-drilled for weight, and come complete with instructions and weight. Just assemble, sand, paint, and add wheels and axles to have a great looking and top-performing car.
Does Key 3 sound intimidating? It's not really that hard, but if you want to skip this key, consider our Official BSA Speed Wheels and Axles. Official BSA Speed Wheels are mold number matched and have been precision-machined for top performance. Official BSA Speed Axles have the burrs and crimps marks removed, a slightly tapered head, and are partially polish. Just a light polishing and these axles are ready to go.
Pinewood Derby Speed Kit To ensure that your car is fast there are a few critical tools and supplies. To ensure that you have these supplies, and to maximize the value of your time, we offer Speed Kits. These Speed Kits include:
- Graphite - The #1 recommended lubricant
- Axle Polishing Kit - For polishing the axles
- Bore Polish - For polishing inside the wheel bores
- Gap Gauge - For setting the wheel to car body gap
- 600 grit sandpaper - For polishing the wheels