and rb is the base radiusSee 6.4.8 for the method of calculating an approximate value of mred. See Clause 9 for the stiffness cγα.Method A is to be preferred for less common transmission designs. A method for deriving approximate values is specified for the following cases:a) pinion on large diameter shaft;b) two neighbouring gears rigidly joined together;c) one big wheel driven by two pinions;d) simple planetary gears;e) idler gears.The ratio of pinion speed to resonance speed is termed the “resonance ratio”, N (n1 is in revolutions per minute):