My son is in the Scouts, and his pack had their annual Pinewood Derby, in which they build a car out of a pine block, some nails and four plastic wheels.

Eryk did all of the design work, the sanding, the painting, and the application of stickers. I was in charge of the wheels and the weight.

The car looked good, sorta like an Indy racer. I read the rules for the race and decided on modifying the wheels so that they had no tread, almost like a plastic washer. The friction was greatly reduced, and I could counterbore the mounting holes such that the wheels were closer to the car body. Since the Pinewood Derby track is an incline that goes to a straightaway, I added metal weights to the back of the car, aft of the rear axle. This allowed the mass of the car to remain on the incline longer, adding extra overall speed down the straightaway.

Well, it worked. My son had the fastest car in his den, and came in fifth overall (the nose of the car bumped the track in the second lane, which threw off the overall time). He was very happy, and I was very proud of him. He hammed it up when they took pictures of the winners.

It's fun to spend time with your kids when they have something to concentrate on.