definitely fun to drive around in the way most "make a weird thing and roll it" games are.
my first impulse was like, maybe if you got to see the course and set the wheels in advance? but i think something that's cool about this design is being able to change how the wheels are inflated on the fly, so losing that seemed like throwing the baby out with the bath.
the idea of the car's weight being what modifies the wheels is still appealing to me, but maybe changing their setup via a menu would give the player the control they need for the design to come together. I hope you keep playing with this idea!