Some 35 odd years ago, I participated in a Pinewood Derby. My father, at the time, worked on the areospace industry and had a very good understanding of the practicalities of physics and how to optimise the weighting to make the car as good as it could be.
Basically the weight added to the car was as high and as far back as the design rules allowed. We ended up using lead sheet crafted to look like an engine mounted above and behind the rear wheels. The car sort of looked like a top fuel dragster with a rear mounted engine and got 2nd place overall on the day.
Another tip from my more recent days of Lego modelling - use a PTFE/silicone oil to lubricate the axle pins.
Hey thanks! The race was last Friday, so it's too late to properly weight my little car now. But this is great info for next time (this Additive Derby is annual). I did lube the axles and that totally helped. The race was a lot of fun (even though I didn't win).