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Weighting Materials: So many choices

What do you use to add weight to your car? Certainly the answer to this
question is not "none!" For without adding weight to the car, it will not
weigh-in at the maximum allowable weight (typically 5 ounces), thus it will
not reach peak performance. Generally 2.5 to 3.5 ounces of weighting
material is required to bring the car to the maximum weight.

So what do you use for weighting material? I have seen people use a variety
of materials such as lead, no-lead weight, pennies, nuts and bolts, fishing
weights, etc. Virtually any material with a non-trivial density can be
used. But there are advantages and disadvantages to the various materials.
In this article we will look at several factors that affect the choice of
weighting material: density, malleability (ease of shaping), cost, safety,
and availability. Density will be given in grams/cubic-centimeter. A lower
density number indicates that the weight will take up more space on the car,
while a higher density number indicates that the weight will use less space
on the car. In addition, the density of each weighting material will be
compared to the density of lead.

Lead - Lead has been the traditional weighting material since the inception
of the pinewood derby. At a density of 11.34, lead is quite dense when
compared to other possible weighting materials. The relatively small amount
of lead required for weighting provides the car builder greater flexibility
in the car design.

An added benefit of lead is that it is very malleable. With most materials
the car builder must create holes or cavities in the car body to fit the
shape and size of the weighting material. However, with lead the builder
can create any size hole/cavity and then shape the lead to fit the hole.
Another nice feature of lead is that it can be easily drilled. Thus, the
weight of the car can be easily reduced at the weigh-in by drilling out of a
portion of the lead.

But as you probably know, lead has a downside. If used improperly, lead is
toxic, so care must be taken when using this material. At our house, we
abide by the following rules:

- Wash your hands after handling lead (and keep your fingers away from your
- Keep lead away from food, water, and food preparation areas.
- Collect and properly dispose of any lead pieces.
- Do not melt lead. The fumes are toxic, and the lead can pop and/or
splatter during the melting process causing eye and skin injuries.

In summary, Lead is clearly a winner in density and malleability. But be
aware of the risks and safety precautions before choosing to use lead as a
weighting material.

Lead Density - 11.34
% Of Lead Density - 100%
Malleability - Very good
Cost - $0.98 per ounce
Safety - Caution advised
Availability - Some Brick and Internet Hobby stores including:
Maximum Velocity

No-lead Weighting Material - No-lead weighting material is available in a
variety of shapes. The material has a density of about 6.30, which is 56%
of the density of lead. Thus, almost twice as much no-lead material is
required versus lead.

No-lead weight is quite hard, so it cannot be shaped. To use no-lead
weight a hole/cavity must be created to fit the shape of the weight. Also,
since no-lead weight is very hard, don't plan on using a drill to reduce the
weight of the car at the weigh-in.

No-lead Weight Density - 6.30
% Of Lead - 56%
Malleability - Very poor
Cost - About $1.99 per ounce
Safety - Okay
Availability - Brick and Internet Hobby stores including:
Maximum Velocity

Pennies - Pennies are a common weighting material, as they are very cheap
and readily available. Generally, a hole is drilled into the bottom or back
of the car (13/16" diameter), and pennies are glued into the hole. How many
pennies do you need? That depends on when they were minted. Prior to 1982,
pennies were comprised of 95% copper and 5% zinc. After 1982, the
composition changed to 97.5% zinc and 2.5% copper (during 1982 both types
were minted). Since copper is more dense than zinc, the older pennies are
heavier. Assuming that you use pennies minted after 1982, 11 pennies is
close to 1 ounce.

Although pennies can be bent if needed, they are not easily shaped. Safety
is not really an issue with pennies, but you should always wash your hands
after handling money.

Penny Density - 7.17 (after 1982); 8.80 (before 1982)
% Of Lead Density - 63% (after 1982); 78% (before 1982)
Malleability - Poor
Cost - $0.11 per ounce
Safety - Okay
Availability - Your pocket or coin jar

Steel - Nuts and bolts (and screws and washers for that matter) are also
commonly used as weighting material. A typical use is to insert screws into
the bottom of a car to fine-tune the weight. Assuming stainless steel, the
density is about 7.70, so it is a bit more dense than pennies. Steel cannot
shaped, and safety is not an issue.

Steel Density - 7.70
% Of Lead Density - 68%
Malleability - Very poor
Cost - About $0.30 per ounce
Safety - Okay
Availability - Hardware Store and Maximum Velocity:
Maximum Velocity

Tungsten - Tungsten is a very dense metal. At a density of 170% of lead,
tungsten is the densest material that is practical for use on pinewood derby
cars. Tungsten is completely non-toxic so it is gaining increased use in
weighting applications where lead is not appropriate. For example lead has
been banned in many streams, so tungsten is often substituted for lead
weight on fishing flies. Tungsten is very hard, so it cannot be shaped or
easily drilled.

Tungsten Density - 19.3
% Of Lead Density - 170%
Malleability - Very poor
Cost - $1.95 to $4.95 per ounce
Safety - Okay
Availability - Some Brick and Internet Hobby stores including:
Maximum Velocity

Other Metals - Other metals exist with greater densities; however, they are
either very expensive or very rare. Both gold and platinum have a higher
density than lead (170% and 189% respectively), but you would end up with a
car that should be locked in a safe!

Summary - What do you use for weighting material? As you can see, there are a variety of choices, so pick the material that best meets your needs.

From Pinewood Derby Times Volume 1, Issue 6

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