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Pinewood Derby Stories and Photos from Maximum Velocity
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Maximum Weight for Performance
Most pinewood derby races specify five ounces as the maximum weight. Ensuring that your car weighs five ounces is an important factor, as tests have repeatedly shown that top performance is achieved at this maximum weight (see "Weight Experiments", in Volume 3, Issue 14: March 31, 2004).
But what if your race rules allow more weight? Should you weight your car beyond five ounces? If so, how heavy should you go?
I ran an experiment to try to ascertain the "magic weight". The experiments were partially successful, but due to a variety of factors, one magic number is not possible. For example, all of the following affect the maximum weight:
- Weight position (balance point) - as the balance point is set more aggressively, additional weight is shifted to the rear wheels, putting more wear on these wheels.
- Lubrication type - as can be seen in this experiment, the type of lube affects the amount of weight that can be used.
- Wheel type - lighter weight wheels will tend to deform under heavier loads.
EXPERIMENT SETUP
The experiment used the following equipment:
- Pinewood Wizard body. This body allows the weight to be easily changed.
- Two sets of Ultralight Speed Wheels from Maximum Velocity - These official BSA wheels weigh 2.2 grams, and are machined with a high level of accuracy. They are structurally strong, so they can carry additional weight.
- Two sets of Speed Axles from Maximum Velocity.
- Tapered tungsten cylinders, and various other tungsten weights.
Car Body The Pinewood Wizard body was set up to weigh 5.0 ounces with the wheels and axles. Additional cylinders and smaller weights were incrementally added to achieve the desired weights. The car was centered weighted(5), and all four wheels were running on the track (see Figure 1).
Figure 1 - Wizard Body
Wheels and Axles The wheels were used right out of the package. The axles were lightly polished and then lubed. The wheels/axles were installed on the car, and the alignment was checked to verify that the car rolled virtually straight.
Lube One set of wheels/axles was lubed with Krytox 100. The other set was lubed with Tube-O-Lube graphite.
Track A 32 foot aluminum Freedom Track was used with a Judge Timer. For each run the car was staged in the left lane.
EXPERIMENT PROCEDURE
The car was first run four times for lube break-in. Then, to minimize lube variance, the tests were made from low to high body weight, and then again from high to low body weight. The sequence was as follows:
1. Three heats were run at 5.0 ounces.
2. One additional ounce of weight was added, and three heats were run. This was repeated up to 10.0 ounces.
3. Three additional heats were run at 10.0 ounces.
4. One ounce of weight was removed, and three heats were run. This was repeated down to 5.0 ounces.
EXPERIMENT RESULTS
The following charts show the results of the test. The plots show the results with the high and low run removed for each weight.
Figure 2 - Results with Krytox 100
Figure 3 - Results with Tube-O-Lube
CONCLUSIONS
For graphite, maximum performance for a center-weighted car is reached at about 9.0 ounces. Likely, the maximum weight for a rear-weighted car would be less. The 6.0 ounce result appears odd. Possibly, the graphite required more break-in time, so the car was not performing at peak until the 7.0 ounce runs. The last three runs at both 5.0 and 6.0 ounces were better than the first three runs.
For Krytox, the results are inconclusive. Performance continued to improve through 10 ounces. Additional tests with a different test body would be needed to determine the maximum weight.
A feature article is a regular part of the Pinewood Derby Times Newsletter. To subscribe to this free e-newsletter, please visit: www.maximum-velocity.com/subscribe.htm
