Three attributes that will help your car go fast.

Weight:  The CO2 cartridges that power your vehicle will release the same amount of CO2 each time. The weight of your car will be a major factor.

Aerodynamics:  Wind friction will slow your car down. The better your car cuts through the air the faster it will go. Use the wind tunnel to test your vehicle.

Friction: Your cars shape, craftsmanship, wheel contact with the floor, and your tires ability to spin freely should all be major concerns.