I am a coach for 2nd grade gravity racers and my students are wondering whether the rubber tires must be included on the 4 wheels that are required? Can they just use the gray plastic wheel without the tire attached?
The rubber tires are not required. The only relevant rule is "4. Teams may use as much or as little of the kit as they wish as long as all four wheels are used to roll the racer on two axles." Wheels and tires are technically two different parts, and the Gravity Racers description never mentions tires.