Original Post @ (http://blog.wired.com/geekdad/2009/02/5-easy-tips-for.html)
It's that time of year again. In schools and churches and community centers around the globe, Cub Scouts are gathering to put their building skills to the test in the annual Pinewood Derby race.
Thankfully, our Cub Scout pack has a category just for dads, so I can build my own car. My son -- although I help with the more difficult and dangerous tasks -- is largely on his own. I believe it's important that his car be his own. That's not to say I haven't searched long and hard to find the best performance tips for making my car as fast as possible.
I'm sharing some of them here.
It's my understanding that there are as many different rule sets as there are packs, so what I've tried to do is keep these tips as universal and broad-based as possible. Be sure to double-check your pack's rules before your first cut into your pine block.
- Put all of your weight in the back. Much has been written about the physics of pinewood derby cars, and this is one rare case in racing where heavy = fast. Aerodynamics have little effect in such a short race, but weight does and putting the weight at the back of the car will make your car faster on the flat of the track. Tungsten weights, in most cases, are best because of their high density.
- Lube the car at the body/wheel friction point. Do not paint the car on the small semicircle point where the wheels meet up with the body (where the wheel well is on the car in your driveway). Rather, sand this point to a smooth finish with a very fine sandpaper. Next, after masking off the body's paint, gently massage some dry graphite into the wood. This will reduce friction and increase wheel speed.
- Spend a fair amount of time on axle prep. Using a file and fine sandpaper, make sure you remove any burrs and defects from the axles, near the head of the nail. Some people will put a number of axles in a power drill and spin them to find the axles that are most straight (and eliminate any with noticeable wobble).
- Make sure your wheels are ready. Depending on your pack rules, polishing (or sanding) the business side of the wheel can improve rolling resistance. You can also massage powdered graphite into the wheel edge to further reduce friction. There are plenty of vendors who sell improved wheels, but if your group is like ours, these are outlawed. You can also polish (with graphite again) the wheel's bore. Once your axles and wheels are finished, a good rule of thumb is that, with a flick of a finger, they should be able to freely spin for 20 seconds.
- Finally, once your wheels are mounted, check their alignment. Find a long board and mark off a racing lane, about 6 inches across. Put the board on a very slight incline and allow your car to roll a few feet. If, at the end of this test run, your car has moved significantly to one side or the other (or the wheels have moved in or out), move the axle up or down to adjust your alignment.
That's it! These are my quick tips for improving your pinewood derby car's speed. Do you have a speed secret that you can share with us for making your car move? Let us know in the comments.
