There are six major factors that influence the speed of a Pinewood Derby car. Pay close attendtion to all six of these and you can build a winning car.
Major Speed Factors:
1. Body Design
2. Weight Placement
3. Wheel Preparation
4. Axle Preparation
Advanced Speed Techniques:
1. Rail Rider Alignment
2. Rear Wheel Canting
3. Advanced Friction Reduction
II. Weight Placement
Where should you place the weight in your Pinewood Derby car? Good question. The pinewood weight placement will have a huge effect on your car’s center of gravity (COG). The center of gravity of your pinewood derby car is the distance that the balance point of the car is in front of the rear axles.
Many people simply tell you to just “put the weight in the back”. While that is true, there is a lot more involved in this process. Proper placement of the COG is crucial in order to have a fast car.
What is COG?
The center of gravity of your car is expressed in inches. It is the distance from the rear axles to the balance point of the fully assembled car. That balance point should always be in front of the rear axles and is usually between 1 to 2 inches.
The exact location of the COG of your car can be determined with the use of the Derby Monkey Center of Gravity Stand or any ruler as follows:
• Set the COG Quick Check or a ruler on its edge on a flat and level surface.
• Carefully lay the car across the COG Quick Ref or ruler.
• Move the car back and forth until it balances.
• This balance point is the COG.
• Measure the distance from the COG to the rear axles.
• This distance is how we express the COG location on a Pinewood Derby car.
Where Do You Want Your COG?
There are many different opinions regarding the pinewood weight placement and where the exact location of the COG should be. However, every one aggrees that you want it close to the rear of the car. Most publications recommend a COG of 1″ to 1½” in front of the rear axles. Most experts agree that this is too far forward. The faster cars seem to be built with a COG of a less than 1″.
Derby Monkey Garage builds its cars with a COG of ¾” in front of the rear axles. Some builders even go with shorter COGs. The FASTEST BSA legal Pinewood Derby Car Kit available anywhere has less than a ¾” COG. This car is the G-FORCE and has won hundreds of races at the pack and district levels. To see the G-FORCE car kit CLICK HERE
The speed of the G-FORCE is due to a combination of factors but one of the most important factors is the short COG. This aggressive COG is achieved by the weight pocket design which allows you to place two rows of ¼″ tungsten cubes behind the rear axle. This car is smoking hot.
Why Does a Short COG Make Your Car Faster?
How fast your car goes on the first flat part of the track is based on the distance that the heaviest part of the car actually travels before it reaches the curved part of the track. The weight mass of a car with the weight in front will not have traveled as far when it reaches the curved section as the weight mass of the car with the weight in the rear. The farther the weight mass travels the more speed the car picks up on the first section of track.
However, if you move the COG too far back the car may become unstable, wobble, pop a wheelie or jump off the track.
If the track you’ll race on is in good condition, very smooth, no rough spots, etc. then go aggressive with a ¾” COG. This works well on most aluminum tracks. If the track is rough, then you should go less aggressive with a 1″ COG. Wooden tracks tend to get rougher with age.
Position the weights in your car so that you have the optimum COG. Tungsten is the best weighting material because of its density. This allows you much more flexibility in controlling your COG.
Remember, the fastest way to check your COG location is with the use of the COG Quick Check below.
How high the weight is in the car is also very important. Your vertical center of mass (COM) should also be very low in the car. The lower the COM the more stable the car will be. That’s why tungsten plates attached to the bottom of the body can help create a very fast car.
There is an abundance of possible weight solutions. You can add anything for weight. Some people use coins, nuts, bolts or fishing weights. There are several commercially available weights that are designed specifically for Pinewood Derby Cars. These consist of lead, zinc, steel and tungsten.
Lead is old school but is very inexpensive. You can melt lead and pour it into a cavity carves in the car body. This is messy and somewhat unsafe but is a method used for many years. You can also purchase lead wire and insert it into holes drilled in the car body. Lead is a hazardous material so great care must be taken when working with this type of weight.
Zinc weights were developed as an alternative to lead. They are much safer than lead but are not as heavy. Zinc weights come in a variety of shapes and sizes.
Steel is a good weight choice and is also available in various shapes and sizes.
The best weight for Pinewood Derby cars is tungsten. Tungsten is more dense than all of the other materials. This means it is heavier than any other pieces of weight of the same size. This allows you to have a low profile car for greater aerodynamics and still have enough room in the wood to add enough weight. Tungsten also allows you to concentrate the majority of the weight exactly where you want it in order to optimize the car’s COG.
Why Tungsten is the Best Pinewood Derby Weight
Tungsten is no doubt the best material for Pinewood Derby weight for several reasons.
• 1.7 times heavier than lead
• 3.2 times heavier than zinc
• Extremely dense allowing you to place a lot of weight in smaller areas
• Allows for more flexibility with COG placement
• Available in a variety of shapes and sizes
• Non toxic
• Environmentally friendly
• Its wicked cool to say “my car is weighted with tungsten”
• Tungsten is more expensive than lead or zinc
• Tungsten is not as easy to find as lead
Popular Tungsten Shapes:
Tungsten Cylinders are probably the most used and most popular tungsten shape. Cylinders are easy to install by first drilling 3/8″ holes in the car body.
Tungsten Cubes are likely the next most used shape. Tungsten cubes are available in various sizes but the most popular are the ¼” cubes. Cubes allow to compact weight in square cut weight pockets. Cubes offer you a lot of control in the placement of your COG.
Tungsten Plates are very useful pinewood derby weight. The plates are approximately 36mm x 20mm x 1.5mm and weigh about 1/2oz each. Plates allow you to attach weight directly to the underside of the car. This is great for keeping the center of mass low in your car. Plates are also god for when running out of room to place weight.
Tungsten Putty has been very popular over the last few years. Putty allows you to add minute amounts of weight in order to get your car to the exact maximum allowable. It also gives you the flexibility to adjust the final weight by simply removing or adding a little at check in.
Tungsten Canopies are also popular because just one piece can be all the weight you need since they come in 2.5 oz and 3.5 oz sizes. Plus, they make your car look super cool.
There are other tungsten configurations for pinewood derby car weights including spheres, discs, granules and powder. Look here for a complete list of Pinewood Derby Tungsten.
How to Install the Weight
Screw On: You can purchase tungsten and zinc plates with small screw holes so that you can screw the weight onto the car… usually on the bottom. When adding a screw on weight make sure that you do not violate the car dimension rules including the 3/8"" bottom clearance rule.
Drill Holes: You can drill 3/8" holes in the car body and insert lead wire, zinc round weights or tungsten cylinders. Glue in place then fill the rest of the hole with wood filler and sand smooth. The car body pictured below has three 3/8" holes drilled for adding weight.
Weight Pockets: You can cut or carve weight pockets on the underside of the car body and glue in almost any type of weight. The G-Force body pictured bellow shows the weight pockets with tungsten cubes glued in place.
BELOW: Car body #1 shows 3/8" holes drilled in the side for lead wire, zinc rounds, steel cylinders or tungsten cylinders. Car body #2 show hold drilled through the top of the car body for the placement of tungsten cylinders. Car body #3 shows the weight pockets on the underside of the G-FORCE body and the tungsten cubes glued into place.