One published guideline for clincher inflation pressure is to pick the value for each wheel that produces a 15% reduction in the distance between that wheel rim and the ground between loaded (i.e. with the rider) and unloaded. Pressures below this lead to increased rolling resistance and likelihood of pinch-flats. Pressures above this lead to less rolling resistance in the tire itself, but to larger energy losses in the frame and rider. Bicycle tires are essentially thin-walled pressure vessels and so the circumferential force in the casing is directly proportional to the internal pressure and to the tire diameter, and the force in the longitudinal direction is half of this.