Friday, May 10, 2013

Five Keys to Performance

I can’t count how many times I have been asked, "How do I make my pinewood derby car go fast?" If you have been involved in pinewood derby racing for any time at all, or if you have been a subscriber to this newsletter, then you understand that there is no simple formula for success, and thus no simple answer to this question. But since I am asked the question, I provide five keys to unlock the performance of pinewood derby cars.


Key 1 - MAXIMIZE MOMENTUM
Maximum weight; Add weight towards the rear of the car

In an automobile, momentum helps the car keep rolling when you take your foot off the gas. In a similar way, momentum helps a pinewood derby car to continue rolling as fast as possible on the flat section of the track. Momentum must be maximized for top performance, and the key to momentum is weight. In each race, there is a maximum allowable weight for the car (usually five ounces, but certainly check your local rules). Momentum is maximized when your car has the maximum allowable weight for your race.

For a five ounce maximum weight, you will likely need to add two or three ounces of weight to the car. But where on the car do you add the weight? Add the weight towards the rear of the car.

Tests show that best performance is achieved on most tracks when the weight is added towards the rear of the car. This can be overdone, but a simple test to make sure the car is properly weighted is to balance the finished car on the edge of a ruler. The car should balance somewhere between 1 and 1-1/4 inches in front of the rear axle.

Does the type of weight matter? The maximum weight can be achieved with any type of weight; however, the type of weight does affect how easily the desired weight can be achieved. Denser weights (such as Lead or Tungsten) take up less space, so it is easier to reach the maximum weight. Also, since denser weights require a smaller volume of space, they allow creation of more aerodynamic cars (which is Key 2).

By the way, if you are in a BSA-sponsored race, ignore the picture on the front of the BSA kit. Use the slot closest to the end of the block as the rear axle.

Key 2 - AERODYNAMICS
Profile and body features minimized to improve air flow

If you asked me a year ago, "How do I make my pinewood derby car go fast?" I would not have included aerodynamics as a key. However, since that time I have read one study and performed another, both of which showed that the effect of aerodynamics on pinewood derby car performance is not trivial (see Volume 3, Issue 9 - "The Big Debates - Aerodynamics").

There are many elaborate ways to improve aerodynamics, but to simplify matters, let's use the following principles:

1. Low-profile cars (smaller surface area as viewed from the front of the car) will tend to outperform higher-profile cars.

2. Cars should taper from a smaller surface area in the front to a (possibly) larger surface area in the rear.

3. Edges running across the car should be rounded or tapered.

4. Wings, sails, flags, pennants, etc. add to the surface area, thus they tend to decrease performance.

5. Unfilled (major) holes can catch air and slow down a car.

To add some balance to this topic, Key 2 (aerodynamics) is not as important as the other four Keys, so I don't suggest that you sacrifice looks to achieve an aerodynamic shape. If your child wants to build a car that is not particularly aerodynamic, don't worry about it. Just make sure that the other four Keys are carefully followed.


Key 3 - WHEEL/AXLE PREPARATION
Axles - no flaws, straight, polished; Wheels - no flaws, polished

All of the frictional losses in a pinewood derby car come from the wheels and axles. Start by inspecting the parts in your kit to make sure they are usable. If a part has a serious flaw, replace it.

Next, prepare the nails.

1. Place the nail in the chuck of a drill and use a Mini-File to remove the flashing under the nail head and minimize the ridges on the shaft. Beveling the nail head slightly is also a good idea.

2. Optionally use the Pro-Axle Press to ensure that the nails are straight and round.

3. Finally, polish the axles with an Axle Polishing Kit until they are bright and shiny.

To prepare the wheels, use the Pro-Hub Tool to square the wheel hub. Then use a Pro-Wheel Mandrel and some fine grit sandpaper to polish the wheels. If allowed by your local rules (and the configuration of your wheels), use the Pro-Hub Tool to cone the inside wheel hubs.


Key 4 - LUBRICATION
Quality lubricant; applied properly

Lubrication is an extremely important key. The difference in time between a well-lubricated car and a car without lubrication can be one-half second or more (this translates into several feet on the track).

Most people use graphite for lubrication. Graphite is carbon that has been ground up into a fine powder. There are many varieties and qualities of graphite available at hobby and hardware stores, so make sure to get a good brand. We offer Tube-O-Lube brand, which has been proven to produce top results in pinewood derby racing.

When lubricating with graphite, take the time to work it in thoroughly; a casual puff before the race is not sufficient. After lubricating, make a few test runs to break in the lubricant (or free spin the wheels several times). Since graphite works best after a break-in period, don't re-lubricate between race heats.

If you use a liquid lube (such as NyOil II), make sure to follow the recommended application procedure. With liquid lubes, less is best.


Key 5 - ALIGNMENT
Car goes straight

In order for the car to get to the finish line as quickly as possible, it needs to go straight. If it zigzags down the track, it will travel a longer distance, but worse it will continually lose speed as it bumps and rubs against the guide rail.

To minimize the amount of alignment adjustment needed, make sure that the axle slots/holes are perfectly parallel to each other and the axles are straight. Also, when using axle slots, make sure that the axles are inserted perfectly straight. The Pro-Axle Press and the Pro-Body Tool are great tools to help minimize the need to align the wheels. In addition, the Pro-Axle Guide will help you insert the wheels and axles properly.

There are a few different alignment procedures, and they vary depending on the use of axle slots or holes. The best procedure is to use shims made from wax paper to adjust the alignment. This procedure is documented in our booklet Speed to the Finish. But a simpler method is as follows:

1. Determine which of the front axles appears to be the most out of alignment (or with a raised wheel, adjust the wheel/axle that is on the ground).

2. Make a mark on that axle where it comes out of the car body.

3. Remove the axle from the car and remove the wheel.

4. Using a vise, pliers, etc. very slightly bend the front axle at the point marked in step 2 (the Pro-Axle Press works well as an axle holder).

5. Replace the wheel and re-insert the axle.

6. Roll the car on a smooth and level surface.

7. If it does not roll straight, slightly rotate the bent axle by grasping the axle head with a pair of pliers.

8. Repeat steps 6 and 7 until the car rolls straight.

CONCLUSION

There are many other things you can do to create a competitive pinewood derby car. If you want to read further, our booklet, Speed to the Finish thoroughly documents the techniques and tips needed to get top speed out of your car.

But whatever you do, just remember that to create a competitive pinewood derby car, don't lose your Five Keys!

From Pinewood Derby Times Volume 6, Issue 1

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