[eNyoron]

You can add more traction to the wheels by adding downward force onto the wheels. Any additional weight would be dispersed by the wheels regardless of where it's centered unless the robot has another point of contact with the ground (or if it goes all the way through the trailer). So you could add force with springs or with pneumatics, thereby adding traction.

But I'm wondering, could you propel yourself by say, pushing off of walls? There have got to be some ways to move outside of the traditional wheels on the ground that are still legal within the competition constraints.