In large airliners, for example, the tiller is often used as the sole means of steering during taxi, and then the rudder is used to steer during takeoff and landing, so that both aerodynamic control surfaces and the landing gear can be controlled simultaneously when the aircraft is moving at aerodynamic speeds. The specified selection criterion, e.g., minimum size, weight, or pressure, are used to select suitable tires and wheels from manufacturer's catalog and industry standards found in the Aircraft Yearbook published by the Tire and Rim Association, Inc. The choice of the main wheel tires is made on the basis of the static loading case. The total main gear load formula_1 is calculated assuming that the aircraft is taxiing at low speed without braking:  where formula_3 is the weight of the aircraft and formula_4 and formula_5 are the distance measured from the aircraft's center of gravity(cg) to the main and nose gear, respectively. The choice of the nose wheel tires is based on the nose wheel load formula_6 during braking at maximum effort:  where formula_8 is the lift, formula_9 is the drag, formula_10 is the thrust, and formula_11 is the height of aircraft cg from the static groundline. Typical values for formula_12 on dry concrete vary from 0.35 for a simple brake system to 0.45 for an automatic brake pressure control system. As both formula_8 and formula_9 are positive, the maximum nose gear load occurs at low speed. Reverse thrust decreases the nose gear load, and hence the condition formula_15 results in the maximum value:  To ensure that the rated loads will not be exceeded in the static and braking conditions, a seven percent safety factor is used in the calculation of the applied loads. Provided that the wheel load and configuration of the landing gear remain unchanged, the weight and volume of the tire will decrease with an increase in inflation pressure. From the flotation standpoint, a decrease in the tire contact area will induce a higher bearing stress on the pavement which may reduce the number of airfields available to the aircraft. Braking will also become less effective due to a reduction in the frictional force between the tires and the ground. In addition, the decrease in the size of the tire, and hence the size of the wheel, could pose a problem if internal brakes are to be fitted inside the wheel rims. The arguments against higher pressure are of such a nature that commercial operators generally prefer the lower pressures in order to maximize tire life and minimize runway stress.