This paper investigates the impact of takt time on the efficiency of automotive assembly lines, focusing on real-world data from various plants in Germany and Japan. Takt time, the average time for the production of a unit to meet customer demand, is found to significantly influence assembly line efficiency. Through empirical analysis of 55 observations, the study reveals a strong nonlinear relationship between takt time and the percentage of value-added time. Shorter takt times correlate with higher efficiency, with a 1% efficiency gain for every 5-s decrease in takt time for takt times between 30 and 120 s. The paper also emphasizes that improvements in manufacturing systems, such as lean tools and work standards, are critical for optimizing efficiency. The results suggest that faster, high-volume lines tend to be more efficient, though continuous improvement remains key.