Weigh In
1. Get the weight as close to the 5 ounce limit as possible. Add the last little bit of weight at the race. Remember, the official scale may not weigh the same as yours.  

2. Everyone has an opinion on where to put the weight. Many believe that the weight needs to be predominantly in the rear so that gravity can act upon the weight further up the incline and for a longer period of time. A car with more 
weight to the rear generally grabs more speed down the slope. Many suggest having the center of gravity at 1 to 11/2 inches in front of the rear wheels. But be careful not to put too much in the rear or you'll pop a wheelie.  

3. What kind of weight? Hobby shops and the scout shop sell special weights for derby cars. Tubular weights can be sunk in the sides; flat weights can be attached to the car bottom if it is carved in a bit. Incremental weights ( with pre-marked grooves) are easier to snap off into the size you need. Some folks just use nuts & bolts, pennies, washers etc., but these must be glued so that they can not move. No movable weights or mercury are allowed.  

4.  You can include the weights in your design and paint them.   

5. Keep the weight low on the car and in the center (Left/Right of the car). Put the weight just in front or behind the rear wheels for less wheel chatter.