How . Im Suppose to build my ballloon car

I haven't really gave a thought about how im suppose to build a balloon car. But i thought that in order for it to reach a certain speed i would like the car to be light weighted. Since the car is lightweighted it would probably go faster since the balloons don't have to drag along a great amount of weight. I want the wheels to be built out of lego tires or those rubber ones that are from those big toy cars. The big wheels are probably going to put weight on the bottom of the car, so that the car would be attached to the ground even though its very light weighted at the top. I would like my car to actually look like a Bugati Veyron as hard as that may sound. Good Luck to me=)