Its all about the pinewood derby wheel spin….. Find the wobble.
In order for your car to be fast, you car to go straight down the track. You need the wheel to spin in its path true through its 360 degree rotation. Assuming your axles are tuned and we have eliminated improper alignment, if you wheel has a wobble, that wobble will be transferred to the movement of the car. This side to side travel of the car is energy that is transferred from pushing the car faster. Any energy that is used other than pushing the car, results in slower times.
First thing to do is when you get your kit, is get 2-3 more sets of wheels from the Scouting Store. This will give you an adequate amount of stock to choose from.
Then you are going to need a solid axle that does not have a head to it. Reason being we want to test rotation of wheel without any other possible variables. The stock BSA axles are not adequate. So we suggest to use a metal shaft no greater than .0930″ in diameter. Pin Gauges work great and can be found here. They are a bit pricey but will yield the most true results. Keep them oiled as tool steel will rust and they will actually get larger with the rust to the point you can no longer use them. If that is not a good choice for you, then the solid axle from PineCar® will do the trick.
Add a little lube to the axle and inside wheel hub to minimize friction for a true spin, then spin with LOW RPM to test for wobble. Slow spin watch the inner bore in relation to the outer tread. Do they spin together or does one travel in a different direction as the other? If your eye is good enough, you might be able to spot the out of center wheels. If not the wheel test will show them too.