According to oil and bike manufacturers their motocycle oils have superior wear protection, engine cleanliness, high-temperature stability, lower volatility/lower oil consumption and often better anti-corrosion performance. For a.m. reasons it is not recommend to use passenger car oils in bikes. http://www.prod.mobil1.com/motorcycle/index.jsp http://www.shell.com/home/Framework?siteId=advance-en&FC1=&FC2=&FC3=%2Fadvance-en%2Fhtml%2Fiwgen%2Fgetting_more%2Fclean_4t_ga_0104.html&FC4=&FC5= OK, most likely it's true. Then why would not we use a good motorcycle oil for 4-stroke engines in a car engines ? Think we may disregard an impact on catalytic converters for the following reasons: 1). lower volatility, if it's so, should offset a higher phosphorous level; 2). higher phosphorous does not yet mean this will damage the converter faster because the process of its giving off depends more on additive chemistry; 3). gas is not perfect everywhere too and it may content so many impurities that they can kill converter earlier then phosphorous. Where the truth ?