Your Pneumatic dragster may be small, but it's going to be moving at incredible speeds when you race it. That means it will be subjected to a wide variety of forces that affect its motion and velocity. Here are some of the principal forces involved:
Mass: Obviously, this is how large and heavy the car is. Simply put, the less weight your dragster has, the faster it will go. This is the most important factor that will figure into your design. Keep it light!
Thrust: The air provider by the compressor to the car. We'll cover this in a bit.
Friction: The second most important fact you'll face. Because the dragster has parts moving against one another, friction is created. You can help reduce it by making sure the axles are free to rotate, and that the wheels and tires are not rubbing on the car body.
Drag: Here's where aerodynamics come into play. As an object moves through the air, it is met with air resistance as speeds increase. This air resistance pushes against your Pneumatic car and prevents it from going as fast as it could in a vacuum. You can't completely ever remove drag, but you can help reduce it by building a more aerodynamic car. Those are more difficult to create.
Since the compressor will be releasing the exact same amount of air pressure in each car, the car that wins the race is the one that is the lightest and most aerodynamic. Think of it as a drag race between two cars with the same engine but different bodies.