I'm Mike, den leader for Den 6, which this year is six Bears (third graders) who are, as of this writing, extremely excited about January. I've been a den leader for three years, I've been to five derbies counting my own boy's, and I have spent more evenings than I'd admit to my wife thinking about the physics of a five-ounce block of pine on a 32-foot track. This page is everything I know, written down so I stop repeating it at den meetings.

Two things before we start. One: every tip on this page is legal under our pack's rules, which are the standard rules that come in the kit plus a few of our own, and I've put them right up top so nobody's surprised at the weigh-in. Check your pack's rules if you're not in 214; they vary. Two: the boy builds the car. Not you. You'll find a whole section on that, because it's the most important thing on the page, and because I've seen a dad cry at a weigh-in and I don't want that to be you.

The one that trips up the most dads every year is the 5.0 ounces. The one that trips up the most boys is the clearance. Measure both twice.

A Pinewood Derby car doesn't have an engine. The only thing pushing it is gravity, from the top of the ramp to the flat. So a heavier car has more energy to spend on the flat part, where the light cars run out of steam. Get as close to 5.0 ounces as you can. The kit block, wheels and axles together weigh about 3-1/2 ounces before you cut anything off, and less after. You'll be adding weight, not taking it away.

Where the weight goes matters almost as much as how much. Put most of it toward the rear of the car, about an inch in front of the rear axle. Here's why: on the sloped part of the track, the higher up the ramp your weight sits, the longer it stays up there being pulled down the hill. A car with its weight in the back is, in effect, starting a little higher. Put the weight too far back, behind the rear axle, and the front wheels get light and the car wobbles. An inch in front of the rear axle is the sweet spot. Balance the finished car on a pencil; it should tip just in front of the rear wheels.

How to add it: The hobby shop sells lead or zinc weights made for this. Drill holes in the bottom of the car (a 3/8-inch bit works for the round weights) or cut a pocket, glue the weights in with wood glue or epoxy, and fill over them with wood putty so nothing can fall out. A weight that falls out on the track is a disqualification and a very sad boy. Bring the car in at about 4.9 ounces on your kitchen scale, because your kitchen scale and the pack scale will disagree, and leave yourself a hole to drop a little more in at the weigh-in.

The axles in the kit are nails. Look at one under a magnifying glass and you'll see three problems: little burrs and a seam along the shaft from the way they're made, crimp marks under the head where the machine held it, and a rough surface all over. Every one of those is friction, and friction is the enemy. Polished axles are the single biggest speed difference between a car that wins the den and a car that doesn't. I'd say it's worth more than everything else on this page put together.

Here's how, and the boy can do every step of this with a grownup holding things:

1. Put the nail in a drill chuck (or a hand drill in a vise) with the head sticking out. Run it slowly.
2. With a small flat file, take off the burrs under the head and along the shaft. Light pressure. You're removing bumps, not metal. A few seconds.
3. Now wet-or-dry sandpaper, a strip about a half inch wide, wrapped around the spinning nail: 400 grit, then 600 grit, then if you've got it 1000 or 1500. Each one for maybe 30 seconds. Keep it moving so you don't cut a groove.
4. Finish with a dab of metal polish (the kind for chrome) on a rag, held against the spinning nail, until it shines like a mirror. Wipe it clean.
5. Do all four. Don't drop them. Put them in a zip-lock bag until it's time to put the wheels on.

Whole job, all four axles: about 45 minutes with a nine-year-old doing the sanding and you holding the drill. You'll be able to see the difference. So will the timer.

The wheels: Look at the tread of each kit wheel. There's usually a little seam or a nub of plastic from the mold ("flash") on the edge. Trim that off with a hobby knife, carefully, and give the tread a light rub with fine sandpaper just to take the glossy bumps down. That's all. Under our rules you can't change the shape of the wheel, and you don't need to. Make sure the hole through the wheel hub is clean; a twist of a pipe cleaner through it works.

Alignment is where good cars go slow. A car whose wheels aren't straight will steer itself into the center guide strip and rub the whole way down. Here's how to check it:

1. Push the axles into the slots straight and square. Tap them in gently with a small hammer, with the car on a scrap of wood so you don't crush the slot. Leave just a hair of play between the wheel and the car body, about the thickness of a piece of cardboard, so the wheel spins free but doesn't wobble.
2. Find a smooth, flat board or a countertop, four feet long, and prop one end up an inch or two.
3. Set the car at the top and let it roll. Watch which way it drifts.
4. If it drifts left, the front wheel on that side is toed in. Pull that axle a tiny bit and re-set it with a very slight tilt, or tap it in a hair deeper on the other side. Tiny adjustments. Roll again. Repeat until it rolls straight for four feet.

This is fiddly and it's the last thing you do before graphite, after paint. Give it a whole evening. A car that rolls straight for four feet on the kitchen floor will run straight for 32 feet in the gym.

Dry powdered graphite comes in a little squeeze tube at the hardware store (it's sold for sticky locks) or the hobby shop. It's the only lubricant our rules allow and it's the only one you'd want anyway. The night before the derby, with the wheels on:

• Puff graphite into the gap between the wheel hub and the car body, and between the hub and the axle head, on all four wheels.
• Spin each wheel with your finger for a good while, 30 seconds or so, to work it in. Puff in more. Spin again. Do this three or four times per wheel.
• Tap the car on a paper towel to knock off the extra. Graphite is messy and it gets on everything, so do it over newspaper, not the dining room table (I'm speaking from experience, and so is my wife).

Some folks graphite the wheels before they put them on, by spinning them on an axle in a drill with graphite in the hub. Both ways work. The main thing is: graphite the night before, spin the wheels a lot, and don't touch it after check-in.

Here's the honest truth: at 32 feet and maybe 12 miles an hour, the shape of the car hardly matters. Weight, axles, alignment and graphite decide the race. A low, thin wedge is a little better than a tall block, mostly because it's easier to put the weight where you want it, but I've seen a car shaped like a bar of soap win the pack. So let the boy make it look like whatever he wants: a wedge, a race car, a shark, a school bus, a stick of butter (we had one). It's his.

Cutting: The boy draws the side view on the block with a pencil. A grownup runs the saw, band saw or coping saw, with the boy watching from a safe distance and saying "a little more off the front." That's the one step a nine-year-old shouldn't do alone, and everybody understands that.

Sanding: All him. 80 grit, then 150, then 220. Takes a couple of evenings. Smooth wood takes paint better.

Paint: Spray paint or brush-on model paint, thin coats, let each one dry all the way. Two or three color coats and a clear coat. Do the paint before the final weigh-in on your kitchen scale, because paint weighs something. Decals, stickers, a driver made of clay, pipe-cleaner flames: all fine, just count the weight. Keep the underside and the axle slots clean of paint so the wheels spin free.

I've been to five derbies and I can tell you which cars the dads built from across the gym. They're beautiful. They're perfect. They've got airbrushed flames and a clear coat you could shave in. And the boy standing next to one is holding it like it's somebody else's, because it is.

Then there's a car with a slightly crooked paint job and a thumbprint in the putty, and the boy holding that one is bouncing, because he made it, and he knows every inch of it, and when it wins its heat he's going to remember it when he's forty. And when it loses its heat, he's going to want to build a better one next year, which is the actual point of the whole thing.

So here's what I ask every family in Den 6:

• He designs it. His idea. Draw it on paper first.
• You cut it (saws), he does everything else he safely can: sanding, drilling the weight holes with you holding the drill, gluing, puttying, painting, polishing the axles with you holding the drill, graphite.
• Explain the why. Why the weight goes in the back. Why the axles have to be smooth. He's a Bear; he's ready for it. That's a science lesson he'll actually remember.
• Your job is patience, safety and the saw. Not the car.
• Let it be a little crooked.

There's a "Dad's Race" after the boys' race, an open class, no rules but the weight. If you've got something to prove, prove it there. Last year's Dad's Race winner spent, by his own admission, forty hours on his car. It was gorgeous. His son's car, which his son built, came in fourth in the pack. Guess which one's on the mantel.

A little bit every couple of weeks beats a panic on January 20. Here's the schedule. Den meetings are Saturday mornings at the church.

Last year's den was Wolves, and they did us proud. Every car passed inspection on the first try, which had never happened before. Here's how it came out. Every boy raced four heats, one in each lane, and places are by total points.

And the Dad's Race was won by Brandon's dad, for the second year running, and we'd all like him to take a year off.