The BSA sells an arbor (or did ~14 years ago when my son raced) that you can mount wheels to. It's like the arbors Dremel sells for cut-off wheels. You may be able to mount it in a drill motor and run it at high speed, creep up on a block of sandpaper. Don't know if the rules have changed or not, but back in the day reshaping the wheels was not allowed, only truing them up.
Pinewood derby racing is basically an exercise in the elimination of friction. The maximum possible speed can be calculated by converting potential energy ( mass x gravitational constant x height) into kinetic energy ( 0.5 times mass times (velocity ^ 2)). Mass cancels out (like Galileo dropping 2 cannonballs of different weight which hit the ground at the same time), so the formula boils down to "Velocity = Sqrt ( 2 X 32.2 ft/sec^2 X height)". A track with a 5 foot tall starting block has a maximum theoretical speed of 17.94 ft/sec or 12.23 mph.
Our son won a lot of races following the rules. We also ran an open race that we won multiple times (no rules). Typical "within the rules" tricks are to work the nails near the head and polish them. They had flash near the head which could be needle filed off, then polished. We trued up wheels on the lathe with the BSA arbor. Then ran the nails with wheels mounted in a drill chuck up to speed and added graphite. Once the graphite was worked in, we spun them up to speed in the drill motor, released the drill motor trigger and timed how long that particular wheel/nail spun until it stopped. We'd get wheels that would spin for anywhere from 20 seconds to about 75 seconds. Naturally, the 75 second wheels/nails went on our son's car.
Another "trick" is to adjust the camber on one of the wheels so it isn't touching the ground. Idea is there's less rolling resistance with 3 wheels touching instead of 4. Also camber the tires so just the edge is touching.
Another one is to carefully push the car on a flat surface (we used the school's gymnasium) and see how straight the car runs. Turn the nails and/or put a little pressure forward/backward to true the steering. Hitting the track bumpers equals friction.
Yet another "legal" trick is to bias the weight to the rear of the car. We biased our son's cars to about 4.5 oz. on the back wheels and 0.5 oz. on the front. The idea was to move the center of mass as far back as possible on the car. When the car is in the starting blocks, the center of mass will be higher than if in the middle, so it's effectively at a higher height than a car with the weight at the front.
For the "open race", we machined the wheels to a knife edge for less rolling resistance. We also used thrust bearings on either side of the wheels. Also put a rare earth magnet in the front of the car. Our starting block was a pivoting dowel with 16D nails sticking up as stops. Our "open" cars were literally thrown down the track at the start; the cars stuck to the nail and when the dowel was spun it gave the cars a good pull for a push start. Totally "legal" in an open race; sure perplexed a lot of dads when they'd see our cars win by large margins.
We never lost a heat on the open races, think my son's cars lost one or two heats but ended up the overall winner every time. Great fun to work with "the boy"!
Thanks for posting and bringing back old memories!
Bruce
