I noticed at my son’s pinewood derby this morning that his car weighed in at 5.1 ounces (the scale they used read out to one decimal place). I was a bit surprised and did a little bit of sanding – surely not enough to even come close to one tenth of an ounce, I thought. Out of curiousity, I weighed again – this time it came in at 5.0 That got me to wondering if the scale actually rounded to the nearest decimal place. Perhaps he really came in at first at just a hair over 5.05 … then my sanding perhaps got him just a hair under 5.05 ounces and then the scale at that point rounded down to 5.0 ….so, it occurred to me that if my theory is right then it’s sort of a way to add an extra 1/20th of an ounce to one’s car and still be “legal” (and thus maximize the potential energy)

Great thought, Mike. Only quibble I have is that I’d love to see your son doing the sanding and getting the car ready on race day. It is his car, after all.

The scale comes with the required two AAA batteries, a three page instruction manual, and a booklet of weight to calorie conversions. Pinewood, plastic, and tungsten are not listed in the book, so I couldn’t look up how many calories a Derby car has. The whole scale is less than two inches tall and comes in a box about the size of a hardback book.

Operation is simple. There’s an off/off button and a button for changing the unit of measurement displayed on the screen. Pressing the on/off button when the scale displays zero will turn it off. Pressing it when the scale shows a weight will tare it to zero. Pressing the Unit button will toggle between the four supported units of measurements. There’s a very large digital readout, located far enough away from the weighing platform to allow unobstructed viewing, even with a large object on the scale. The readout is capable of displaying in grams, kilograms, ounces, or pounds. Accuracy is 0.05 of an ounce, more than enough for most pinewood uses. The scale features a three minute auto shut-off to preserve the batteries if you forget to turn it off.

The weighing platform on the scale is slightly too small to hold a BSA pinewood car with a standard wheelbase. Placing a car on it causes the wheels to roll off the side. To weigh your car on this, you’ll need to do it without the wheels attached. You can also place a small wooden block on the scale and tare the scale with this block on it, using the block to lift your wheels off the surface of the scale. Since I always add weight to my cars before attaching the wheels (I weigh the wheels separately first), this isn’t a problem for me, but might be an inconvenience for others.

My review copy would occasionally briefly fluctuate 0.05 ounces above and below the actual weight, always returning to and settling on the correct weight again after a moment. This doesn’t make the scale unusable, but does require that you spend a moment looking at the scale to make sure the weight has settled.

The platform size probably prevents this from being used as the official scale at a pinewood derby. This would be a useful scale for personal use and testing, however. The small size means it fits easily in most toolkits, the battery operation allows you to use it anywhere, and the inexpensive price point allows you to have your own scale without breaking the bank. The fact you can measure down to five hundredths of an ounce means you can get your car as close as possible to the magic weight limit, much closer than you can get with a scale reading only tenths of an ounce.

In 1953, Don Murphy made Cub Scout history when he founded the Pinewood Derby. Over 50 years later, his son Donn is here talk about the race you grew up with and he inspired.

For pictures from last year’s race, see the “2008 CSCA Pinewood Derby” set on Flickr.

The problem with this logic is twofold. We’re not just testing the rate at which something falls; on most tracks, half the track is sloped and half is flat. And we aren’t running in a vacuum; there’s lots of friction involved.

The only propulsion your car gets is the conversion of potential energy to kinetic energy as it rolls down the sloped portion of the track. Once it reaches the flat part of the track the only thing that keeps it going is the energy it already has. The more energy it has when it reaches this point, the faster it will go.

Let’s perform an imaginary experiment. Imagine that bowling ball and that feather both dropped from 3 feet in a vacuum. Both will reach the ground at the same time, but they’ll have very different amounts of energy when they hit. Now, put an egg under both before you drop them. The egg underneath the feather will survive the impact. But when the bowling ball hits the egg — well, let’s just be glad this was an imaginary experiment.

The bowling ball had more energy after its fall because it weighed more. A Pinewood car that weighs more will have more energy after it “falls” down the slope of the track. And more energy is good, beacause that’s what keeps the car speeding along.

Last year our Scout District race was held outside on a car lot in April. Almost every car that showed up was weighing in at 5.1 ounces — a tenth of an ounce too heavy. One disgruntled father set out to prove that our scale was wrong and produced a 5 ounce brass tare weight. We put the weight on the scale and it came in at exactly 5 ounces. The scale was right, all the cars were too heavy.

Every one of these cars had raced previously in their Pack races. Were the scales at all the other races wrong? Had everyone added weight between races? Why were they coming in so heavy?

Most pack races were held in the winter and early spring when the air was drier. The combination of the more humid air in April and the race being held outdoors caused the cars to absorb just enough moisture to tip the scales. Racers and their parents were scrambing to remove weights with drills, by breaking off car parts, and other extreme measures. If only they had an easy adjustment method.

Previously I suggested drilling a few holes and plugging them with screws. Put a tenth of an ounce of your weight in these holes. Then on race day, you can add and remove weight easily by simply dropping weighted beads into those holes. That method works and has served me for years, but I’ve got another method I’m using this year.

Hardware stores carry lead tape for use in balancing fans and other applications. This year our cars will be built to weight 4.8 ounces and we’ll have plenty of lead tape on hand. A few strips on the bottom of the car will push the weight to the limit. And if we end up too heavy, we can simply trim a little of the tape off.

The BSA kits are terrible. The wheels are out of round, unbalanced, have crooked axle holes, varying wheel bore diameters, and uneven surfaces. The blocks aren’t square, the axle slots are poorly cut, and they have different vibration dampening qualities. The axles are crooked, have different diameters, and the nail heads aren’t perpendicular to the shafts.

Some kits are better than others. If you restrict a boy to using a kit as-is, and allow no modifications from stock, you are reducing the race to chance. All fairness has been eliminated and the kid who happens to get a good set of wheels or a straight block suddenly has an unearned advantage. You might as well not hold the race and just flip a coin to determine the winners.

This is the third in a series of articles aimed at race officials. In the series you’ll learn why complicated rules hurt the kids and the integrity of the race.

This is madness.

All this complexity is going to lead to mistakes, arguments, and more problems than you would believe.

When creating complicated rule sets, people tend to create many rules are subjective or are difficult to enforce. How do the race inspectors examining wheels ensure that they weren’t lathed? Are they weighing each wheel? Visually, lathed wheels can appear to be completely stock. Some races have prohibitions on cars from previous years or on pre-cut cars. The intent is to keep kids from using last year’s car. I agree with the intentions — building the car is part of the fun. But who can tell for certain which cars are pre-cut or a re-paint of their older brother’s car? Rules like this should be presented as guidelines that should be followed instead of rules that should be enforced.

The problem with trying to create a rule to cover every possible situation is that you can’t possibly think of every possible situation. Even baseball, which has hundreds of individual rules — including ones to cover things like animals getting onto a field or a ball getting stuck in your sock — understands that the rules can’t cover everything (they made a rule to cover that problem). The more complicated you make your rules, the more impossible they will be to enforce. You’ll introduce conflicts, ambiguities, and loopholes — just look at the US tax code.

Simplify your rules. It will make your race more enjoyable by far.

This is the second in a series of articles aimed at race officials. In the series you’ll learn why complicated rules hurt the kids and the integrity of the race.

This is the first in a series of articles aimed at race officials. In the series you’ll learn why complicated rules hurt the kids and the integrity of the race.

In sports, the kid who’s faster, stronger, and more skilled than the rest is praised. His talents are rewarded. But in pinewood derby, the geeky kids who like math and physics are told that their talents are an unfair advantage. The kids who spend the time researching the science behind building a winning car are considered cheaters and next year we’re going to create a rule to prevent them from being creative and coming up with new ideas.

Sure, there are some dads who will do lots of the work on the cars and build an unfairly fast car. But do you think your rules and restrictions are preventing this? All you’re doing is eliminating the easy adjustments the average kid can make and understand. The complicated tricks and techniques aren’t prohibited and you’ve just made it more likely that the winning car was built by dad.

My car last year had four-wheel independent suspension, low-energy wheels, a low-inertia design, and minimized braking friction with all the advantages of bushings and washers. It was something that no kid is likely to be able to build. It was also completely legal according to most sets of rules I’ve seen.

What are you going to do when a kid enters a car like that?