The study aimed at analyzing the relationship between assembly ergonomics, assemblability (“ease of assembly”), and product quality and at quantifying these relationships in economic terms. This was in order to better to support the development of more ergonomic product and assembly solutions, particularly at early stages of the car development process. The assembly of 24,443 cars was studied for 8 weeks in an assembly plant and for another 16 weeks as factory-complete vehicles. The results show increased risks for quality errors of 3.0 and 3.7 times and total action costs that were 8.7 times and 8.2 times higher for high and medium physical load assemblies compared to low physical load assemblies for 55 tasks assessed.