When designing a WIRL car, you must follow the WIRL car
specifications. Currently there are Four official classes used for WIRL racing. Visit the
following pages to review the specs for each class:
Below is a simplified chart to explain the basic
differences between classes:
There are many sources of information for
Building Pinewood Derby Cars on the web. For this guide, we provide some very
basic information. For more advanced technical instructions, we suggest you
visit the forums at
Derby Worx Pro Board or Derby Talk
Wood and Shape: The shape of the car can be anything from a simple wedge
to a complex shape. It all depends on your skill level. Try to keep it
aerodynamic, but keep in mind the car shape is not nearly as critical as other
factors we will discuss later on. When shaping the car, keep in mind that you
will have to allow for the paint thickness, or you may go over length. For
instance, if you shape a piece of bare wood to exactly 7" long, and later paint
it with 3 coats of paint and a coat of acrylic, the car will end up over length.
Take the time while shaping to plan for a space near the rear of the car to
place your weights. You may need to drill or cut out a special compartment for
this purpose.
Weight: To put it as simply as possible, the heavier the car, the faster
it will go. Your goal will be to make the car as close to 5 ounces as possible,
without going over. An accurate scale is necessary. If you are not sure about
the accuracy of the scale you are using, design the car so there is a small
amount of weight you can remove if it goes over. Place the weight toward the
rear of the car. Be careful that the weight doesn't protrude from the bottom of
the body or you may have clearance problems. Because of the dangers of handling
lead, we recommend using weights such as tungsten. Attach the weights securely,
so they do not come loose during the race. This could result in
disqualification. WIRL weighs the cars to an accuracy of 1/10th ounce.
Paint: If you are working on the car with a child, this is a good time to give them paint, stickers, decals, and let them go. Paint jobs are never critical to winning races, and this is a great way to let the child put their imagination and creativity to work. Actually, it is not even a requirement that the car needs to be finished at all!
However, if you want to attempt a "pro" paint job on your car, here are a few basic tips:
The Key to a good paint job is patience. To do it properly, you must paint, dry,
sand,
& clean each coat. The minimum for a decent result would be 2 coats of primer and 2 coats of paint. Spraying on the paint gives better results than using a brush. To start, sand the car with a fine sandpaper to make the surface as smooth as possible. If the grain of the wood is rough in spots, you may want to use a wood filler to smooth it out. Before you begin painting, place toothpicks or wire in the axle slots to prevent them from closing up during the painting process. The smoother the surface before painting, the better the finished paint job will be.
Begin the painting process by spraying on a light colored primer. Applying a thin coat will avoid drips and bubbles. Let the primer coat dry overnight, sand the car with a very fine (800) wet/dry sandpaper, wipe or wash the dust off, then apply another thin primer coat. Repeat the process until you have a primer coat with good uniform coverage (usually 2 to 3 coats). After this you are ready to paint. Again, use thin coats to prevent drippage. Spray enamel is generally easier to work with, but spray lacquer produces a harder finish with more sheen and depth. Whatever you decide to use, read and follow the instructions and always work in a well ventilated area.
After you apply the paint coats, you may add decals or pinstripes if you wish. Top it off with a clear coat or two for a protective finish.
Wheels: Preparing the wheels is a
very important part of your car construction. In WIRL there are two different
types of wheels that have very different rules: Check the
specs for approved brands as new brands may be added at any time. These types of wheels are made with a mold and often they have mold irregularities that cause them not to roll well. Run each wheel across a smooth flat surface to check how well they roll. Most likely you will need to lightly sand the tread surface to make them roll smoothly, but don't overdo it! Reshaped stock wheels will get your car disqualified for stock division. Keep the tread contact surface flat on your stock wheels.
Modified wheels are a different type of wheel. As long as the diameter and material specifications are met, they can be any shape. Most modified cars end up with disc-shaped wheels that are razor thin. The idea behind this is, the less surface area on the track=less friction. Eliminating friction will make the car go faster down the track. Modified wheels can be made with a lathe, or there are several companies that now manufacture disc-style modified wheels.
Another factor to consider when choosing the wheels is the hardness of the plastic. Generally, the harder the wheel, the faster it
will run.
Axles: You must make sure that the axles you use on your car are not bent or warped. Place the head of each axle just off the edge of a flat table surface, then roll the axle along the edge using your fingers. If the axle or axle head wobbles, you have a bent axle. Another common issue with axles is they will often have tiny burrs on the surface that can cause friction against the wheel and slow the car down. Use a polishing compound such as fine pumice. It is better to use a fine granulation and polish it down slowly, rather than accidentally overpolish and take off too much metal.
Alignment: Alignment is a very important factor if you want to have a fast car. Wobbling cars that bump against the rails lose time, so the object is to adjust the wheels and axles in relation to the body so it rolls straight and true. You don't need a 42 ft track to test your finished car (although it helps!) A single six or seven foot section with a slight downhill grade will allow you to see how willing the car will be to roll straight. Keep adjusting-again patience is the key. Also this stage is the time to make sure the wheels aren't too tight against the body of the car. Try to keep a 1/16" to 1/8" gap between the body and the wheels by leaving a bit of axle space.
Lube:
Axle lube will get your wheels spinning faster! WIRL allows any type of lube that is dry at race time and not shedding excessively off the car. A popular form of lube is graphite, and in fact, in some derbies this is the only type of lube allowed. Other popular choices include Nyoil II, SB-10, and Elmer's Slide-All. Whatever you do, use something to lube your wheels.
Apply the lube to the axle, then run the car lightly on a flat surface to evenly distribute the lube around the axles and wheels, then repeat the process.
Show Cars:
When building a show car you will want to keep in mind the judges will be
looking for the following 3 aspects:
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Shape: The shape of the car is the first factor to consider. How
well executed is the carving? How visually pleasing is the shape? How
difficult was the shaping of the car? Do attached objects add to the shape in
a uniform way?
-
Finish: Is the paint smooth and free of bubbles, etc. How well are
the paint, decals, and trim items applied? Do they add to the overall theme of
the car?
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Concept: What is the theme of the car? Does the car name explain the concept?
How clever, creative, or unusual is the Car's theme?
These factors should give you an idea of how to build a great show car. WIRL
rules state the bottom of the car will not be judged, so concentrate on the
topside
Parting tips for woodcar builders:
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Remember to leave an unfinished section of wood on the bottom of the car
for the WIRL stamp.
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Don't attach items to the bottom of the car as it may affect the clearance
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Also it is a good idea to write the car and builder name on the bottom of
the car
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Don't over-tweak the car. Sometimes in woodcar building, less is more!
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Above all, HAVE FUN!
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For advanced expert tips, visit
Derby Worx Pro Board or Derby Talk
