Yes, when you polish the rest of the nail, polish the head of the nail also. The part that touches the wheel. So when you polish the wheel bore, also polish the face of the wheel where it touches the nail head. A fast car will have low friction and go down the track straight, not bouncing off the rail. My kids(me) usually shaped the car similar to the one in MyMiata's post, but honestly sometimes they wanted something weird and it was still fast if it was well built
I've helped my nephew build a couple. He finished really well with his first one, and it had unmodified wheels and axles nailed into place by a 7 year old who had never held a hammer before.
I carved one into the shape of a 911 cabrio when I was a Scout. What a car nerd. I wonder if I still have it?
My favorite was one with my son. He wanted it to look like a shark. The final product went down the track with the bloodied arm of one of his sister's dolls hanging out of it's mouth.
It was still pretty fast.
You can buy axles that have been modified for low surface area and they don't cost much. Wheels on the other hand can be surprisingly expensive.
One year I was a little weary of it all and I was just going to slap one together out of the box instead of all the extra work but then one of the parents started mouthing off how he was going to embarass us so all I did was polish the boy scout wheels and axles , got the alignment close and ran it. It was very close to our other ones with aftermarket parts, and faster than the other families who also had aftermarket wheels and axles
In reply to SV reX :
You can make the weight, or even buy weight that fits inside the wheel, I assume the rear wheels. They don't move but I assume this is a favorable location for some weight.
The engineering on this can be fun,but as most others have mentioned other people attitudes can be annoying. If you're fast they say you're cheating
In reply to BlindPirate :
The weights DO move. They rotate. That's not allowed.
Honestly, I don't see the reason to cheat. There is a great amount of variation and speed available just from being careful and detailed.
Coincidentally I was in a hobby store today, and they had a whole array of tools for optimizing a Derby car, stuff I didn't know existed, There were jigs to straighten and polish the nail axles or to align them during installation, alignment tools, micro polishing kits, various lubricants, a little lathe for truing the wheels, all kinds of lead and tungsten weights, high speed wheels (that were marked not Derby legal), even some heavy liquid stuff that can be put inside a cavity that will shift the weight from rear to front. There were also kits with various dress-up accessories like engines, exhaust pipes, drivers, decals, and so on.
I participated in the Pinewood Derby as a Cub Scout in the middle 1960s and things were a lot simpler then. The cars were basically blocks of wood that were meant to be carved into sort-of replicas of an old style front engine Indy car, they had different style wheels from what is used today, and no one had thought of any of the high tech tricks that are apparently common today. My cars were weighted to get close to the limit using some of my dad's lead bullets, they were used to replicate carb intakes and exhaust pipes. 
I still have my cars, they're sitting on the shelf above my computer monitor.
A topic near and dear to my heart. I've done three generation of them now and ran the program for the pack. When I was a scout I brought a tempera painted block of wood with wheels to the race. One of the dads looked at it, shook his head, and helped me get it working enough to get down the entire track to the end. I still appreciate that. When my son was a scout, I ran clinics so that the kids without dads (usually) or with dads too busy to help would have a chance to put together a car that could run. And I made a cheat sheet for how to make them fast - weight/axles/wheels/etc.. Back then google wasn't available to make you an expert in five minutes so it was useful.
First, the oil thing. I found plastic compatible super lightweight oil and tested against graphite. IIRC it was watch oil from German and I actually imported two weights. Was not as fast as graphite. Standard dino oil would soften the plastic over time.
The "how to go fast" info is all out there on the internet, but in my experience the two most important things are 1) the most weight you can have up high, but far enough forward so the car is stable. 2) And make sure the car runs dead straight and smooth. Beyond that most of the tweaks are for small advantage which you may need to run with the fast guys.
When my son was building these we'd buy three cars. I built one and he followed my example and built two, running the faster one. This way the car was totally his, for better or worse. One year we had access to a machine shop so he got some experience on a digital lathe. Wasn't the fastest car we built. But there could be no complaints that "dad built the car" if he won. (he didn't)
I tried all the "tricks" with my two sons, we never won but they usually finished well. I did make them sand, paint etc. their cars (some of the kids first time touching "their" car was when they carried it in). We cut the handle off a black plastic spoon on one of them and glued it on for a cool looking canopy. One year my oldest son decided to paint the car yellow with a blue stripe....he won best "Cub Scout Themed Car" and he was happy even though that never even entered our thought process!! Another year it was blue with a red spider web on it and won "Best Non-Cub Scout Themed Car"...a trick also was that I used the same scale they used and would make the car too heavy and decrease the weight until it was "exact" ... due to the tolerance in the scale it could weigh a small fraction of an ounce more than adding weight to make it "exact"...
I enjoyed the Rain Gutter Regatta better as it was more about the boy and their technique....
Some of my favorite childhood memories revolved around the pinewood derby. You can see my progression over 3 years, from the yellow roadster with sick hand-painted flames, then the 2nd place red car, then my 1st place pack win with the silver car. This would have been Y2K era, so the early internet existed but all the speed secrets were still hard to find. The yellow car was terrible but I whittled most of it by hand with my shiny new leatherman I got that year. I loved building that first car. Our den leader had a wood shop, so I got to learn how to use tools like band saw for the other two cars. The dads got smart that year. Our whole den had lifted and drilled front wheels, better weight placement, and all the graphite, and we swept the pack competition.
The pack-winning silver car went to regionals but it was pretty disappointing. It rode too low and bottomed out on the regional track. I recall the experience being very crowded, loud, and similar to how SVreX described it. Dad got us out of there quick once my car failed. If I get to this in the future with a child, I will let them guide how they want to do things. I feel like the internet has ruined some of the trial and error that makes this fun. I had no idea what I was doing with the yellow car but I think I had the most fun with it.
I run our Trail Life Troop pinewood derby event every year. Every year I build a "near max effort" car within the rules. I've only been the fastest car once, and not by much over a random nine year old doing whatever. I only have nine rules, but inspired by GRM, the ninth rule is "don't make me name a rule after you" and I playfully read the riot act to the Dad's ahead of time. I hold up an old car I have and say "This car is from 1990 or so. Guess who built it?" Everyone guesses me. "Nope, it's my sisters. I built mine with my Dad. What that means is that he built it while he yelled at me. I went out in the first round and threw it into the garbage can later that day. Don't be that guy. My sister built this for fun with our Grandfather, didn't even get to race it, and she still has it today." So our stuff is under control. I do one run in every lane of two tracks, lineup is whoever happens to be in line with you, and I record finishing position only.
Everyone. EVERYONE. has fun. I always give my car away to a deserving kid.
maschinenbau said:Some of my favorite childhood memories revolved around the pinewood derby. You can see my progression over 3 years, from the yellow roadster with sick hand-painted flames, then the 2nd place red car, then my 1st place pack win with the silver car.
I got a third place trophy back in the 1960s but it was only about 2" tall. 
Working with my 7 year old nephew on his car. James did the design, almost all the cutting and shaping along with 100% of the painting and hammering and adding of random stickers. The car was not the prettiest, but it was clearly his work and he was super-proud of it.
The next year, with his younger brother Thomas supervising. That lime/white car on the left is one I mostly made for Thomas the year before with his supervision. Thomas has never entered a pinewood derby, he just likes making stuff. Naturally, he was in charge of paint. Those kids love rattlecans.
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