Rotational Inertia

There is something rarely talked about.

Rotational inertia.  Take a ball and quickly twist/rotate it in your hand. Now take a ruler and rotate/flap it back and forth. The ball's mass is compact, so rotates easily.  The ruler's is long and has its mass distributed along its entire length. The end of the rulers are far away from where you are rotating your wrist, so it takes more effort to stop and reverse direction.  This is rotational inertia.

The same thing happens in your pinewood derby car.  Most tracks slide down and then quickly curve at the bottom.  Those that have their weight distributed along the car nose to back will have more inertia, taking more effort to go into the curve. Those with weights that are compact aligned will navigate the curve with less rotational inertia.

If you want your son to win, he will not be using zinc weights. But if he is, drill your holes close together and go into the side of the car, not the back. I encourage lead or tungsten weights, which are already very dense by putting them together in the weight pocket.  They will be naturally aligned along the back in tight rows. Rotational inertail issue minimized.