The body is the foundation of the car and is the place where the Race Team can let their creativity shine! If the Race Team follows most of the techniques in the other chapters of this book, then they will have a fast car regardless of what design they choose for their car body. However, this book examines how professional Pinewood Derby® league racers build their cars. With league racers, speed will always be the primary factor in the shape of the car body. Therefore, aerodynamics is what drives the design.
Not all Race Teams can access the tools required to build a full-on league-style car. Therefore, let’s first look at a more accessible option with decent aerodynamic characteristics and can be plenty fast.
The Wedge Car:
The wedge car is relatively easy to make; cut the block from the kit in half diagonally. This is accomplished using one of several types of hand saws (tooth saw, hacksaw, coping saw, etc.) or with power tools such as a bandsaw, jigsaw or scroll saw. Holes are drilled in the car’s top, sides, or rear for weights.
A word about the dog bone
A body type that has gained in popularity over the years in Scout and other similar races is the “dog bone” or “hourglass” shaped car. Its main feature is the removal of most of the wood in the center of the car, with only a small rod or thin portion connecting the front and rear of the car where the axles and weight go.
The primary thought process behind this body design is to remove as much wood weight as possible so that weight can be relocated in more advantageous areas (i.e., the rear), maximizing potential energy. While this thinking is sound, and these body types can be fast, they are NOT as fast as traditional “Thin to Win” pro style cars.
The reason is mainly due to aerodynamics. Notice the airflow over these two bodies. The dog bone car must move the same air out of the way twice while going down the track, a definite disadvantage.
Professional League style car
The often repeated mantra among league racers regarding the car body is “Thin to Win!” In other words, a thin body is the fastest. As a Pinewood Derby® car speeds down the track, it has to move the air it encounters out of the way. This pushing of the air creates drag and slows the car. Therefore, with all other things being equal, a car with the smallest area pushing against the air will be the fastest.
The other main advantage of a thin car is it helps to maximize potential energy. The slender bodies are much lighter than more traditional designs. By removing most of the wood weight from the car body, the racer can place the weight in the optimal location for maximum speed. Weight placement is discussed in more detail in the Weighting article.
While the thin, lower-weight cars are faster, they can be challenging and time-consuming to construct. These cars use special weights that need to be installed in specific locations in the car. Also, additional materials (hobby-grade thin plywood, vinyl, etc.) may be necessary to complete the body.
There are three body types or methods of construction for league-style cars.
Type 1 - Router built with full integrated top. These car bodies are built using a hand router or CNC router to cut out pockets on the bottom of the car for the weights and remove unneeded material from the body. These bodies tend to be .3125 to .375 inches thick.
Guides or templates (click here for free plans) can be created to help make this type of body using a hand router. Alternatively, CNC cut bodies from official BSA blocks are available here.
Type 2 - Cut through with a separate top (AKA “ladder body”). These bodies are built using a coping saw by hand, a scroll saw, or a CNC router/laser. For hand cutting, the design is sketched onto the wood block. A hole is drilled through the block that allows the saw blade to pass through so the builder can cut the interior features of the body. A top needs to be added (glued) to the car. League racers prefer 1/64-inch thick plywood for this purpose. The plywood is light but very strong and imparts a fair amount of rigidity to the body. League racers will often cover the car with colored vinyl to keep weight to a minimum. Guides or templates (click here for free plans) can be created to help make this type of body. Alternatively, CNC cut bodies from official BSA blocks and 1/64 plywood for the top are available here.
Type 3 - Hybrid cut through/router built. This option has pockets for the weights routed into the body, but all other areas are cut through. League racers will often cover the car with colored vinyl to keep weight to a minimum.
A fourth option employed by some professional racers consists of building the car frame from individual wood pieces, also known as “stick building.” Stick building is an advanced technique that is not practical for most Scout Race Teams and is outside the scope of this article.
PRO RACER TIP FROM Castoro Racing: Do not make the sides of your car body too thin. The body can start to flex, absorbing energy that could otherwise propel the car down the track.
Wheelbase
One of the primary keys to a fast Pinewood Derby® car is getting as much weight as far back in the car body as possible without the car becoming unstable, thereby increasing potential energy. Weighting the car is discussed in more detail in the Weighting article. However, the car’s wheelbase is essential in maximizing potential energy.
The standard BSA block from the kit has slots for the wheel axles precut in them:
Many races do not require the use of the precut slots. If this is the case with your race, you will want to move the axle locations and drill new axle holes, leading to a faster car!
Moving the front wheels forward can help increase the car’s stability, allowing more weight to be added to the rear.
However, as with most facets of Pinewood Derby®, there is a trade-off between speed and stability regarding wheelbases. The shorter the wheelbase, the more potential there is for speed. However, the shorter wheelbase can also lead to instability, slowing the car.
Speed and stability
Consider the two cars below; both are at the same position on the track where it transitions from the hill to the flat. However, notice with the longer wheelbase car, the front wheels are on the flat part of the track and are starting to slow it down. While in the same spot, the shorter wheelbase car still has both the front and rear wheels on the hill and therefore has yet to lose speed. This is a slight difference; however, races can be decided by ten thousandths (0.0001) of a second, so even small amounts can have an impact!
When determining a wheelbase for their car, the Race Team must consider the track condition they’ll be racing on. For example, on a smooth aluminum track, a wheelbase of 4.75” offers a good balance between speed and stability. For a rougher track where instability could be a concern, the Race Team might consider going with a 5.0” to 5.25” wheelbase.
New axle holes must be made to move or extend the car’s wheelbase. Holes can be drilled using a drill press. However, for maximum speed, it is critically important the holes are placed in precise locations relative to one another. The reasons for this are discussed in detail in the Alignment article. There are tools available that have been designed specifically for this purpose. The car body fits into the tool, and the axle holes are drilled in the correct positions.
Body/wheel contact
Before the car’s final assembly, a portion of the body must be addressed. A significant friction point on a Pinewood Derby® car is where the wheels can contact the body. This friction point is around the axle slots/holes:
If painting the Pinewood Derby® car body, you will want to mask off or tape over this area. Paint, even when dry, can be quite sticky, so you’ll want to have bare wood around the axles.
Here are three options that will significantly reduce the friction between the wheel and the car body:
OPTION 1: Graphite
If using graphite as your lubricant, rub a generous amount on the bare wood using a cotton swab. You’ll want the wood to be as smooth as possible so sanding this area with high-grit paper is beneficial. It’s best to sand this area before you paint. When applying the graphite, you will want to cover (masking or painter’s tape) the painted area around the wood to keep graphite off other parts of the car. Make several graphite applications; you can’t do too much.
OPTION 2: Glue
Super Glue™, commonly referred to as CA (Cyanoacrylate) - CA can be used with any lubrication. First, mask off the car, so just the wood around the axle hole shows. Next, apply glue around the hole. CA doesn’t take long to dry (cure), and a fluid that dramatically speeds up the curing process, known as “activator”, can be used. After the glue cures, sand it with 400-grit sandpaper to level it out. Next, clean off any dust and add another layer of glue. Repeat this process 2-4 times, sanding with the 400-grit paper once cured. You may need to remask with tape around the hole, as the sanding of the glue may wear off the tape. Once there is a good layer of glue, sand with increasingly higher grits of sandpaper (i.e., 800, 1000, 1500, 2000, 3000, etc.). Your goal is to create a very smooth and shiny surface. Once done, apply a coat or two of your wheel wax/sealer, making sure to let it haze over, then buff it out. If using graphite as your lubricant, there is an additional step you’ll want to perform in this area; however, this is covered in the Lubrication article.
OPTION 3: Teflon™ PTFE (polytetrafluoroethylene) Film
This hyper-slippery tape/sticker can be attached to the car body with the axle passing through the center.
Articles in this series (click to read):