This paper shows how design of experiments can be used with a ring-pack simulation program to optimise the design of a piston-ring assembly. Ten factors are varied—six describing the ring profile, three ring tensions, and the lubricant viscosity. Statistical analysis shows that there are some significant interactions between some of the factors—an issue that should be considered when performing test- bed measurements on engines. It is shown that an improved design can be achieved that reduces ring losses by 57% whilst reducing upward oil flow by 39%. This could lead to a 7% improvement in fuel economy provided there are no deleterious effects in other parts of the engine.