– Feature Article – Weighting Materials: So many choices!
– Pinewood Derby Car Showcase
– Memory – Second Chance
Weighting Materials: So many choices
(This article was first published in Volume 1, Issue 6 (December 12, 2001) of this newsletter).
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 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 face).
- Keep lead away from food, water, and food preparation areas.
- Collect and properly dispose of any lead pieces.
- Do not sand, saw, or file lead. Lead particles will be created which cannot be easily collected.
- 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 – $0.75 to $1.15 per ounce
Safety – Caution advised
Zinc (or ‘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. So 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.
The weights sold at hobby shops under the brand name ‘PineCar’ are zinc (BSA branded weights sold at scout shops are also zinc). Several of these products are intended for mounting underneath the car with screws. Be aware that if the weights are attached directly to the bottom of the car, the 3/8 inch clearance specification will likely not be met. To ensure adequate clearance, a pocket must be milled into the bottom of the car to accept the weight.
No-lead Weight Density – 6.30
% Of Lead – 56%
Malleability – Very poor
Cost – $1.16 to $1.75 per ounce
Safety – Okay
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
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 be 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
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 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 (essentially the same as pure gold)
% Of Lead Density – 170%
Malleability – Very poor
Cost – $2.95 to $4.99 per ounce
Safety – Okay
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!
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.
Pinewood Derby Car Showcase
Strawberry Shortcake: Randy West
The Strawberry Shortcake car was the idea of my little girl, who is four years old. The car had a head from one of her dolls that was hard to part with, but we finally came to an agreement. Her car was FAST. The girls could only race for fun, but my little girl’s car won all three races.
The Bandit: Ross & Tyler Bragg
The Bandit, a Speeder design from Maximum Velocity, was the overall pack winner. It weight exactly five ounces, runs on three wheels, has ‘perfect’ balance, and is equipped with matching wheels, and polished speed axles.
Fire Truck: Jim Mason
My Tiger Cub wanted to make another fire truck for his pinewood derby car this year. After two previous years in the Sibling Division with a fire truck, we decided to ‘make it a go’ again. We had watched the TLC channel show, “Overhaulin'” together, so I suggested we design a fire truck and make it look like a hotrod. We went on the Internet and found a photo of a 1946 Ford Fire truck and we were off and running. The light on his truck does work when it rolls down the hill; and other than wood, there is little weight added. We cut the side pieces and saved the new top from the rear cut, and then we glued it all together and painted it. The car (truck) looks great, but I wish we would have taken more time filling in with wood filler. My son loved the design and even won a trophy at our pack race. He then took third in the Tiger Division at District, along with Best Design. He was thrilled!
Pinewood Derby Memory
After flying all night March 23rd, I arrived at my home in Wisconsin at about 6 in the morning. After a short nap, I began setting up our test track. We were participating in the Cub Scout Pinewood Derby on Saturday and I only had two days to complete my work on these little 7 inch blocks of wood. Ryan (my 9 year old) had sanded his car to the shape he wanted, so now it was my turn. I promised to make it fast by helping him polish the axles and wheels. When Ryan got home from school, we began working on his car. The next day, I continued to work on Ryan’s car, then Joyce’s car, and then my car (for the parent’s race) the rest of the day Friday so I could have Saturday morning to go with our family to a church breakfast. It was hosted by a farmer from our church (Cedrick) who has his own Sugar Bush. A Sugar Bush is an area where maple syrup is produced.
After pancakes and sausage, (this experience would probably spoil any diet you were on. Myself, I could not stop eating pancakes! Something about the environment and all the sweet maple syrup boiling right there in front of me!!) we headed over to the town hall where the Cub Scouts were setting up for the pinewood derby race. I weighed each of our cars on their scale to qualify for the race. Only two of the three were a fraction of an ounce over the maximum weight of five ounces. I planned on being over, you don’t want to be underweight (at our race the judge does not have to tell you if you’re underweight, only if you’re overweight). I had purposely put extra lead weight underneath each car so I could easily drill out the extra lead. Then I offered to help with whatever needed to be done to get ready for the race. The leader’s wife asked me “Do you want to man the concession stand?” and I said, “No, but I will” and was immediately put behind the concession stand selling cookies, hot dogs, drinks and stuff, and test runs. If you wanted to do a test run on the track, you had to buy a raffle ticket for fifty cents. I was able to get a test run in on all three cars before taking over the concession stand. We did a Wolff Family Team race and it turned out just like it did at home on our test track.
When the race started, three cars ran at a time, and at the end points were totaled for each car. I think that is a nice way to do it; it keeps all the boys involved and excited right up to the end. Ryan won the first half-dozen races and then took a second. He then won another half-dozen races and took another second. From that point on, we knew he was not going to be in first place and were hoping for just a second or third. As the race progressed it seemed that cars which we previously beat were now beating us. I took a look at Ryan’s car and found that a piece of decoration (a special homemade decal), had unstuck itself from the side of the car and was rubbing up against the rear wheels. Ryan complained because when I removed the decal, it ripped paint off with it. I apologized and added “you already won the prize for “Fastest Looking Car”. The boys voted on “Best Looking”, “Most Awesome” and “Fastest Looking” and the Cub Scout Master broke-up the racing with announcements of the winners of those awards. But it was too late to fulfill the “Fastest Looking” title, we had already lost too many races. They announced the top three cars and my son Ryan was not in the top three.
Next was the parents’ race and I was first up against two other fathers. My car had button-like wheels (Outlaw Wheels), special axles and tungsten weights that I had purchased from Maximum Velocity. I was racing against a yellow car and a silver colored car. The silver car took off like a rocket leaving me a few feet behind. A few feet out of a 30 foot long track is a very significant win … I think my mouth dropped open. Then he (the owner of the silver car) took his car off the track to return it to the race table, but when he set it down on the table, it took off again! He had incorporated a windup spring into the car to propel it down the track.
Now you’re probably thinking, “That’s cheating”. But, back about the time when we started planning this race, the Cub Scout Master had said “There will be two rules for the adult race 1) It must be five ounces or less, and 2) It must fit on the track. So we all had a laugh. Even funnier was the fact that the Cub Scout Master (Bill) broke rule number two. He built his car too tall, so we had to remove the electronic timer, which formed a bridge over the track and judge the winners the old fashion way using eye balls. So in the end, I took second place and Joyce took fifth.
After the race was over, I was helping clean up when I decided to ask Bill what place my son Ryan took in the overall finishing positions. He looked it up in his computer and found that he had overlooked Ryan’s score. He said “Oh no, Ryan actually tied for third place. I should have had a run-off race”. I asked him if he could send our name to the District Executive as “Tied for Third”? He agreed to do that, and that just made my day. You see, I know I could have done some other things to Ryan’s car to make it faster, but I did not have the time. I could have tried some different things and run more tests. Now Ryan and I have a second chance.
My grandson would like to put headlights and maybe taillights on his car. How is this done?
You can buy little LED lights from Radio Shack. You would then need to run wires back to a battery. A switch would also be needed, or the batteries would die fairly quickly. You would need to check the voltage rating on the LEDs to determine the battery(s) to use.
Blinking LEDs are also available. Since they are off part of the time, the batteries last longer.
In either case, the trickiest part is mounting the batteries in such a way that they can be replaced, but yet be firmly held in place.
The balance point of our car is about 1/2 inch in front of the rear axle. I am concerned about doing a ‘wheelie’ in the transition area of the track. Should I be?
A balance point of 1/2 inch in front of the rear axle is extremely aggressive. If:
- the wheels are perfectly round and smooth,
- the track is very smooth, including the joints,
- the track is normal length (less than 42 feet), and
- Rail-Riding alignment is used
then you may be okay. But if any of these are off, the car could lose traction on the front end resulting in rapid weaving on the flat, or wheel orbiting on the front wheels, both of which will result in a serious slowdown.
For non-Rail-Riding cars I recommend a balance point of 3/4 to 1 inch in front of the rear axle for most tracks.
How does weight affect the car’s speed?
Weight affects the car in three ways:
- More weight (up to a point) improves speed by providing greater momentum, which keeps the car rolling longer at speed on the flat section of the track.
- Positioning the weight towards the rear of the car increases potential energy, providing more velocity on the flat section of the track.
- More compact weight placement reduces the rotational inertia of the car as it transitions the curve, which increases speed.