AbstractA previously developed piston ring lubrication model has been further extended so that the piston ring frictional losses can be predicted in both hydrodynamic lubrication and metal‐to‐metal contact regions for various engine operating conditions. Ring friction results for two engine types are presented for both hot motoring and engine firing conditions. The hot motoring predictions were found to be in good agreement with tests. Results show that when the engine is motored, piston ring friction losses in the hydrodynamic lubrication region predominate. If the engine is fired, the losses in the metal‐to‐metal contact region become dominant due to high gas pressure and temperature effects. Ring friction loss can be significantly reduced by using low tension rings with a correct ring sliding face profile.