Building a soap box derby car is a great project for the whole family. Before building a car, know your competition rules for the derby you are entering. Design your plan on graph paper, making the lines dark enough to see through tracing paper. Draw the top and side view of the car.

Cut the wood to fit your design by placing the tracing paper over the wood. Using a hard lead pencil or carpenter’s pencil, outline the car onto the wood with dark lines for ease of cutting.

Cars with a wider wheelbase tend to be faster, however make sure the competition you are entering allows for this design. Some, such as the San Diego 500 allow the wider wheelbase.

Mark the areas you want to cut for the wheels. You do not want the wheel to extend over the end of the body of the car. Keep within seven inches for overall length, including the wheels. It is important to cut axle slots equally on either side of the body, to allow for a good alignment. Ensure the holes allow for plenty of wood under the axles by placing them at the top of the slots. Slide the axles into the slots to open up the holes all the way. Remove the axles and set them aside. They will be installed again once the paint dries on the car.

The total finished project will weigh around 2.5 ounces, or 71 grams. The cars for competition are allowed to weight up to 5.0 ounces, however make sure you add the weights if you are going for competitive racing. The racing cars need to have weight to overcome the friction created by wheels turning on the track.

Attach either pre-drilled zinc or lead weights to the outer portion of the car. If you place weights underneath the car, make sure they don’t hang too far. The placement of the weights in the back creates a better steering action for the front wheels.

When drilling the car body to place the wheel or axle, make sure you have enough wood around the hole to allow for the drilling procedure without tearing the wood completely through. Drill at least 2 to three holes with 3/8” diameter, each hole being 1 ½” each. Seal the holes by using the body putty, such as Bondo. Sand the filler.

Apply your paint. The first coat will soak into the wood quickly. Paint several coats to seal the wood. Application of a wood sealer is a good way to begin the painting of your car. The sealer acts like a primer and will allow for fewer coats of paint to complete the project.

Add the wheels. Make sure the wheels spin easily, without hesitation. Apply a lubricant if needed. Sand any spots of the car where the wheels may ‘catch’, causing the car to slow down.

Test the wheels by flicking the wheel with your finger. A good spin should run about 20 to 30 seconds, then come to a stop. Examine your clearance, axles and lubrication if they don’t spin well enough. Make corrections if needed.

Check the alignment. Draw a straight line with chalk on a smooth surface. Test the car by running it along the surface.

Complete your construction of the derby car by testing and testing again. Better to be sure now rather than on race day!

For the record, billy carts are motor-less vehicles usually with only space for a small, fearless driver. Using gravity and the steepest hills in their neighbourhood, billy carts have been known to reach speeds of 50 km/h and more.

Billy carts were originally built from wooden crates used to transport soap (thus the name soapbox car) and wheels stolen from roller skates. As with most things, however, the modern billy cart is now a little more sophisticated. While many billy carts are still made from wood, these days you will find some with materials such as aluminium, fibreglass and carbon fibre. There are even purpose-built wheels available.

In the search for improved speed, comfort and safety the billy cart has certainly changed.

While billy carts are usually the domain of children, these days it’s also not unusual to see adults having a go. With the advent of organised competitions, often called billy cart derbies, adults have also caught on to the fun and excitement of strapping themselves into a light machine and hurtling themselves down a hill.

While many of these competitions are more about fun and fundraising than performance, in Australia there is a national championships held annually in Corowa. Held on Easter Saturday, the Australian Billy Cart Championships is labelled as an event for all ages. The event sees competitors racing down the main street of Corowa in their home-made or professionally developed machines.