One can slightly file or bevel the bearing surface of the wheel to reduce the amount of friction touching the car surface. It is strongly recommended that one refrain from using weights which contain toxic levels of lead. Details are important. A high gloss finish. The length should be suitably long enough to allow the cars to accelerate and maintain speed.
Some cars start fast, others maintain speed better.
The best cars do both. The starting gate should be made so that all cars start at the same time. A lane strip is used to force the cars to follow a set path down the track. Sufficient cushioning should be placed at the end of the track to catch the cars and thus avoid damage. For ruggedness, permanent joints should be glued with white glue and screwed.