Length and Wheelbase

The length of your Pinewood Derby car is very simple to choose. The rules state a maximum 7-inch length. You want the car to be that long, minus just a little bit (say 1/16") to allow for judging and measurement slop.

Selecting the wheelbase is very rules-sensitive. Get out your copy of the rules for your Pack/District. Are you forced to use the built-in slots? That's too bad. However, you can at least make the direction work in your favor. The kit slots aren't the same distance from the end of the car, and by making the rear end of the car the one with the slot closer to the end of the block, you keep the wheels on the slope just a fraction of a second longer and gain just a smidgen more speed. (Remember the discussion about locating the center of gravity to maximize potential energy!)

If, on the other hand, you are permitted to relocate the wheels, you definitely want to maximize the wheelbase of the car. The rules dictate an overall length and state that the wheels cannot project beyond the end of the car. In general, the longer the wheelbase, the straighter the car will run, the fewer times it will bump the guide rail, and the faster it will be. Therefore, you want to drill your axle holes so the outside edges of the wheels are just barely inside the ends of the car. 1/16" is a good guideline, although if you do a lot of sanding and either end is "pointy", you may want to allow 1/8", just in case.

The next question is, "do all four wheels have to roll"? What does that mean? Simple: If the rules state that only three wheels have to roll when the car is placed on a perfectly flat surface (our district uses a piece of plate glass), you can "lift" one front wheel by drilling its axle hole 1/32" to 1/16" higher than the other three wheels.

Why have only three wheels touching? Elementary physics. Given that the frictional losses are mainly due to the friction of wheels and axles, a car with only three wheels touching the track will have 1/4 less friction than one with all four rolling. This makes a huge difference!!

Big cautionary note: Please read and re-read your rules to make sure the above techniques are "legal" by the rules.