Along with Wheels and Axles, weighting is one of the primary areas of speed. The proper placement of weight will maximize the potential energy of your Pinewood Derby® car.
Generally, what you use as weight matters LESS than where you put the weight. Youth Race Teams may have limitations on the weights they can obtain. Therefore, the racer can use almost anything; coins, batteries, bolts, washers, etc., are all excellent options. Please note that many Youth organizations discourage the use of lead over safety concerns. Most craft stores will have inexpensive weights available. However, if maximizing speed is your goal, you will want to invest in tungsten. Tungsten is about 1.7 times the density of lead and is available in 0.25-inch cubes and solid bars making them ideal for weighting and balancing fast Pinewood Derby® cars. The weights can be easily removed and used again in future cars! Practically all Pinewood Derby® professional racers use tungsten bars. Use tungsten putty to fine-tune the car’s weight as close as possible without going over! Tungsten cubes, bars and putty are all available here.
There are two primary goals when weighting a car:
Get as close to the allowed maximum weight (typically 5.0 ounces or 141.75 grams) without going over.
Get as much weight as possible, as far back in the body as possible, while remaining stable.
PRO RACER TIP FROM Castoro Racing: A car that weighs 5.044 ounces (143 grams) will register as 5.0 on a scale that weighs to only a tenth of an ounce. Use this to maximize your potential energy if your official scale only measures to one decimal place!
Why does the weight need to be in the rear of the car? To illustrate, let’s look at a car with weight in two different locations; all of the weight in the back and all of the weight in the front.
There is a point on the track where the car transitions from being on the hill to running on the flat part of the track.
Notice the rear weight is still on the hill and falling, pushing the car. The front weight on the flat part of the track is no longer falling, therefore no longer pushing (or, in this case, pulling) the car. The extra push made by the rear weight significantly affects the car’s speed once it is on the flat portion of the track!
Watch the video clip below to see a properly weighted car pull away from the competition on the flat portion of the track!
As you move weight toward the back of the car, you increase the load born by the rear wheels and decrease the load handled by the front. There is a point where there can be enough weight in the rear to raise the front wheels off the track, or at least make it so there is not enough downforce on the front to keep the car going straight. This imbalance leads to an unstable car that will wiggle or, in extreme cases, jump off the track.
Weight balance and distribution
A balance must be struck between maximizing weight in the rear and keeping the car stable as it races down the track. Two methods are used to balance and distribute the weight in a Pinewood Derby® car.
METHOD 1: Traditional
Traditionally, weighting is accomplished by adjusting the car’s center of gravity (COG) by moving the weight forward and backward while targeting a specific balance point.
Here are general guidelines for balancing cars using this method:
For smooth tracks, set the balance point at 0.75 to 1.0 inch in front of the rear axle
For rough tracks, target 1.0 to 1.50 inches in front of the rear axle
Keep in mind these are just guidelines; you may be able to (or need to) go outside these parameters for your car.
PRO RACER TIP FROM DWS Racing: A car with the COG further back has greater potential for more speed but becomes increasingly difficult to achieve stability. Therefore, if you cannot test on a track, it is best to be cautious and set the COG at least 1 to 1½ inches in front of the rear axle.
METHOD 2: Pro
Professional league racers are not concerned with only the COG of the car from front to back but also the weight distribution from side to side. Therefore, they use a different method to weight their cars. Rather than targeting a specific balance point, they look at the load carried by each wheel.
Traditionally professional league racers have used three scales to determine their weight balance. Each of the three wheels that support the car’s weight is placed on its own scale.
Weight is moved around the body to arrive at the target weight distribution for each wheel. The racer’s goal is to find the amount of weight on the front wheel that results in a stable car and maximizes potential energy.
Three scales are not necessary to use this method; here is an option that allows the Race Team to accomplish the same using only one scale!
Here are target values for weight on the front wheel. Many factors should be considered when weighting the car, including track conditions, steer amount, design of car body, etc.
The weight distribution on the rear wheels is dependent on the contour of the track:
PRO RACER TIP FROM HurriCrane Racing: You can put less weight on the front wheel for tracks with a gradual transition from the hill to the flat.
Once the correct weight distribution is determined, the weights can be affixed to the car using double-sided tape and covered with foil tape.
Articles in this series (click to read):