Wheels and Axles
Wheel shape, smoothness and weight are important factors in having a fast Pinewood Derby Car. The shape of the wheel needs to be as round as possible. The tread surface (area that touches the track) should be as smooth as possible. And the lighter the wheel, the faster the wheel (considering shape and smoothness are consistent).
In 2009 BSA came out with a new wheel. They no longer have the little dimple molding mark on the tread surface, it appears the wheels are now being somewhat machined. So roundness is not so much a factor anymore and plus you do not have to remove the molding mark. This will even the playing field for many scouts. It is best to match up the wheels with the same molding number found on the inside wall of the wheel. This way you have wheels that came from the same manufacturing machine they were made from. Better consistency in wheels makes for a faster car as well.
With the new wheels now being machined, the tread surface is much smoother and doesn't require a lot of sanding. You will still want to polish the inside hub of the wheel where it rides on the axle. This can be done with either a non-metal pipe cleaner or the shaft of a Q-Tip installed into a drill. Use a good plastic polish, apply to the pipe cleaner or
Q-Tip and turn the drill on slow while sliding the wheel hub onto the rotating pipe cleaner. Make sure you clean out all the polish from the wheel hub after this process.
Lastly, the lighter the wheel, the faster the wheel - with all things being equal. A lighter wheel will have less rolling resistance, in other words it will take less force to get the wheel rolling and keep it rolling than if it were heavier than it's competitions. Most scouting organizations don't allow lightened wheels in their competition unless the rules allow you to. Lightened wheels are a huge speed advantage. The main thing for you to do, is to not paint them or try to add weight to them, keep them as light as possible. If you do need to add weight to them to get them in balance, use fingernail polish inside the inner wheel. Balancing the wheel will increase speed also.
Putting all the pieces in place and knowing some fun tricks of the trade may make you a parts geek but a winning one at that. Whether it's pinewood derby cars or the vehicle you drive everyday, you want the best derby accessories and cheap auto parts at a high quality to keep both running at top speed.
The axles are the 4 nails that come with the kit. They will have molding marks or burrs on them that need to be removed. You can do this by putting the nail in the drill chuck and using a steel file or even a fingernail file to remove the burrs from the head and shaft of the nail. Be sure to only take off enough to knock the burrs off. You want the nail to stay as large and as round as possible for your fast car. You can also use the file to give the head of the nail a taper so the wheel hub will have less friction when riding against the nail. Just angle the file against the head while it's spinning in the drill.
Next you will want to start with some course grit wet sandpaper and begin smoothing the axle down. Cut the paper so you can hold it against 1/4" of the shaft from the nail head. Make sure you dip the sandpaper in water and hold for only 10 seconds each. Move to finer sandpaper each time you perform this procedure. Go down to the finest paper you can find 1200 grit works well.
You can finish off the axle with some Mother's Billet Metal Polishing compound. This will make the axle shine and bring it to a very smooth fiinish.
Install axles into wheels
Using dry graphite (I suggest Hob-E-Lube) pour into the wheel hub and then install the axle into the hub and spin the wheel to a stop for 10 times. Do this same process two more times, adding graphite as you go. Once you have finished, keep that particular axle with that wheel, you have now matched them together. Perform this procedure for all four wheels.
Getting your wheels and axles to a super smooth finish is critical in building a fast pinewood derby car. Take your time and be patient while sanding and polishing.