<p>The article reviews interrelation of wear speeds of the accelerating and decelerating <br /> gears’ teeth heads and legs, at an account of the ratio of a relative wear of the teeth depending <br /> on the number of gear teeth participating in meshing and gear ratio. Regularities of wear rate <br /> changes between gear teeth head and foot, hardened by bulk hardening, hardening by high <br /> frequency current, cementation and nitriding, in the presence and absence of abrasive particles <br /> in the working environment, when the gear ratio has increasing (accelerating) or decreasing <br /> (reducing) tendency, have been established. Hardness laws of the friction surfaces of the driven <br /> gear wheel teeth friction surfaces of the accelerating and reducing gears have been determined.</p>