Success! =)

It works! My three-wheel design worked!

I had two wheels in front, and one in the back (the back one is supported with Knex pieces and kabob sticks) and the balloon is attached to a straw that goes through the foam and propels it from the ground.

In terms of trial runs, this car works a lot better than the previous one. I got rid of one CD and 54 square inches of foam, making it much lighter. My only concern is that it pulls a bit to the left, but I'll be fixing the back wheel today as I noticed I alligned it incorrectly.

Trial runs:

(The first one I accidentally forgot to convert into cm, since I was measuring in inches)

Because of the turning issue, it kept hitting the dining table.

After leaning it to the right a bit, it went the full way, across the hall and the living room, and hit the wall with a thud. Clearly I'm going to need a bigger trial area!

I'll update with more trial runs after the car is fixed. I'll most likely be taking it outside to see how it performs.