This is definitely a two-person operation, so it is an ideal parent-son cooperative step. If you can find a tile floor that is level and has smooth joints between the tile, and has a clear stretch of between 30' and 40', you're all set. If the floor is tiled with typical 9" or 12" tiles, you will have the reference marks you need, built in.

The object of this exercise is to get the car to roll so straight that it will stay on a single 12" line of tile for at least 30 to 40 feet. Any deviation from that must be corrected.

Steps in the process:

• Sit at opposite ends of the floor, at least 30' apart, lined up on the same line of tile.
• Roll the car to each other and observe which direction it curves off to the side. If it always goes to the same side of the room (i.e. curves left one direction, right the other), you have a floor that isn't level enough and you need to find a different location for this testing.
• If, on the other hand, the car consistently turns to its left or its right, you should adjust the steering as follows:
• Gently pull the "running" front wheel out of the body of the car.
• Using the drill bit in your hand (no mechanical aids, please!), gently turn it and press it at an angle so it cuts just a little bit from the inside end of the hole where it intersects the vertical "steering holes" drilled through the body. Better to do too little and have to re-do than to do too much the first time, so a light touch is required.
• Now, press the axle back into the hole, using the plastic shim to control the final wheel/body spacing. Then take one of the brads and wedge it between the axle hole and the axle where the tip of the axle sticks into the "steering hole." Whether you put the brad in front of or behind the point of the axle depends on which direction you're trying to bias the car's steering.
• Now repeat the "roll it back and forth" process and make successively smaller adjustments to the hole and the amount of the brad that is pressed into the hole in front of or behind the axle until the car runs absolutely straight. You may find that if you just slightly overcorrect the car, you can make better final adjustments by adding a second brad on the opposite side of the axle as the first one. How much patience you and your son have and how much time you take to make the car run really straight will have a lot to do with how well you finish on race day.
• When you are satisfied with the car's steering, put a dab of hot-melt glue on the end of the axle and the brad(s) to hold them all in place inside the "steering hole."