Plastic gears are manufactured cost-effectively in large quantities. They are primarily used in low power applications. However, the continuous development of polymer materials is leading to a growing number of applications in higher performance classes. As a result, plastic gears can also be used in transmissions for e-bikes and small electric vehicles, where the acoustics of the drivetrain are important. In literature, plastic gears are often presented as a low-noise alternative to steel gears. Recent results from system test rigs show that the substitution of individual steel gears with plastic does not necessarily lead to a lower excitation behavior. Based on this, a more detailed consideration of the excitation behavior of plastic gears is of great importance. One value that can be used to assess the excitation behavior is the transmission error, which evaluates the non-uniform motion component of the rotary transmission. The transmission error is largely dependent on the stiffness behavior of the gearing, which is influenced not only by the tooth geometry but also by the material. While the Young’s modulus of steel may be assumed as constant in usual gearbox operating conditions, the elastic modulus of polymers is dependent on temperature and load frequency due to the viscoelastic material behavior. This paper investigates the influence of material properties on the transmission error. For this purpose, the static transmission error of two different polymers (POM, PEEK) is measured at different temperatures and loads on a component test rig. Tests with a steel gear pair serve as reference. The experiments are complemented by measurements of structure-borne vibration, which can be used to correlate the transmission error with the excitation behavior. By comparing the measured transmission errors with those calculated using analytical calculation programs, an outlook on the applicability of current calculation methods, primarily developed for calculating steel gears, for plastic gears is given.