The connection between transmission error and noise and vibration during operation has long been
established. Calculation methods have developed to describe the influence such thatit is possible to evaluate
the relative effect of applying a specific modification at the design stage. The calculations can allow the
designer to minimize the excitation from the gear pair engagement at a specific load. This paper explains the
theory behind transmission error and the reasoning behind the method of applying the modifications through
mapping the surface profiles and deducing the load sharing. It can be used to explain the results of later
experimental validation on various types of tip relief in low contact ratio (LCR) gears, from very long to very
short. The paper will also demonstrate that though the effects of modification in any specific case can be
modeled with some certainty, the same modifying strategy can not be applied universally but must consider
the required operating conditions. It ilustrates that the effect of tip relief on transmission error and load sharing
is not a black art but can be fully explained by applying existing theory.