<p>This study presents a comprehensive comparative analysis of tribological and thermal properties of PA-based composites, investigating PA66 reinforced with short glass fibers containing PTFE/silicone versus PA6 reinforced with glass beads in gear pairings. Durability lifetime tests were performed to analyze the tribological behavior of steel pinion and driven composite gear systems under controlled torque conditions at high, medium, and low loadings at room temperature to investigate load-failure mechanism correlations. DSC measurements were performed to research how glass transition temperature (<i>T</i>_g) and different crystallization behaviors impact lifetime performance. Abrasive wear on gear flanks was measured to evaluate the impact of glass reinforcements on friction properties. Thermal feedback regarding gear operation was obtained through infrared camera measurements of gear surface temperatures. Results demonstrate that thermal monitoring reveals temperature spikes exceeding 20&#xa0;°C precede failure, with PA6 reinforced with glass beads exhibiting thermal runaway at high torques while PA66 with glass fibers and PTFE/silicone maintains steady-state thermal profiles. PA6 with glass beads demonstrates superior low-torque performance through isotropic reinforcement, whereas PA66 with glass fibers and PTFE/silicone provides consistent high-torque reliability via internal lubrication mechanisms.</p>