A fantastic core and upper body exercise.
Place hands on the ground and feet up on the tyre wall. Move side ways by bringing hands together and apart. Move feet slowly around the edge of the tyre too. Once you have completed a full lap around the tyre, change directions and go back. Keep your butt down and shoulders over your hands.
Variations: You can have up to 4 people doing this at once, just start them at different quadrants of the tyre. Make it easier by only going halfway around the tyre and back.