Here's the skinny on pinewood derby cars, or, as the Girl Scouts call them, powder puff derby cars (really, not fooling).....
You need the weight as far back on the car as possible. Use tungsten weights. They can concentrate the weight even more towards the back. The reason for being so far back is this:
The track is a hill at the start, then levels out to a flat plane.
The only time the car is accelerating is when it's dropping down, not going forward.
So, you want the weight as far up that hill as possible so it has the most distance on the hill to keep accelerating before leveling out on the flat plane.
By putting the weight at the very back of the car, in a concentrated mass like tungsten, that's where it'll do the most good.
Now lets talk axles... nails, as some people call them. Put the nail in a dremel tool and spin it on some very fine emery cloth, but not too much. Just to get it polished a bit.
Now here's the best secret.... build a three-wheeled car.
Why? Less friction, less drag.
Pre-drill your axle holes in the wood, but drill the front right or front left axle (doesn't matter which) 1/16" higher than the other three.... so when you mount the wheels and axles to the car, you should be able to set the car on a flat surface and one of the front wheels will be juuuust off the ground by about 1/32". You should be able to press your finger on that high corner and rock the car up and down just a tad.
So now you want to pack dry graphite powder into the hole on the wheel, slip the polished nail axle through the hole, and pack a bit more graphite in the hole for good measure.
Push the nail into the pre-drilled hole, but don't press it all the way in.
Take a butter tub lid, and cut a credit card sized flat piece out of it. Then cut a slot in it to fit around the axle nail. Using that as a spacer between the wooden car and plastic wheel, you can now tap the nail home every so gently, until the wheel is firm against the butter tub lid. Then slip the butter tub lid out and you have a perfectly spaced wheel from the body. Repeat for the other three wheels.
As for body shape, ideally, you'd want a very low and narrow wedge, just high enough to mount the wooden cross members for the axle supports. By removing as much weight as possible from the front of the car and using tungsten weights at the very back of the car to bring it up to 5oz, you've now created the best chance for the longest push with as little friction before leveling out on the flat.
In all reality, when it's done, it would resemble a modern day rear engined dragster, but with the wheel set out farther to fit on the track.
Come race day, when they set five cars on the track, and drop the starting gate, your car will literally BLAST a couple feet ahead of the other cars so fast it will look like it was shot out of a catapult. You'll hear a sucking of air, a millisecond of silence, then "OOOOOOOOooo!!" from the crowd, followed by murmurs of "dad built that car" :laughing:
So how did we figure this out? My kid built a normal car, looked great, ran good, but the kid across the street had a car that looked professionally made, just like all her 4H projects that her mom and dad did for her. She won by a long shot. My kid had enough, so she set her goal to beat that kid the next year. Not very girl scouty, and not a good lesson to learn about that sort of thing..... but hey, she had a goal and went after it. She started googling stuff, and we built it together. I'd cut a scrap piece, then show her how to cut scrap pieces, and she kept at it until she had a car she liked. She sanded and painted everything, drilled all the holes, mounted all the weights, etc... I can honestly say she researched and built the car herself.
So in the end, on race day, she ran 5 heats, took 1st place in the senior division, and beat the 2nd place neighbor kid by a cumulative .002 or .003 seconds over 5 rounds! It was THAT close! :thumbsup: And she was very happy. I got the evil eyes from a bunch of parents, but some guy always does that day, so what the heck. Victory is sweet! :licking:
