at bikes! We take students and adults up the Gap Road in the Humvee and head back down on our FAT Bikes! The large volume low pressure tires act as shock absorbers. They have the comfort of an air ride equipped semi, but with the maneuverability of a sports car. 3.8-inch tires grab up traction on slick or loose surfaces, floating you down the mountain road. Fat Tire Bikes are offered all summer long.