It's called the "3 ball wear test" and the SAE uses that test to rate oils. The measurements taken are wear, heat generation at different pressures and speeds, and at what point the metals begin to fuse or gaul. There is another factor that is of concern when you are talking about cars that get driven only on short trips durring good weather, that is the ability of the oil to suspend water in solution. When the hot car is parked, it sucks air into the crank case as it cools, this process is repeated as hot days and cool nights cause the air to expand and contract. condensation forms within the crank. Since the engin block stays cool as it sits, the condensation builds up in the oil pan. This is the reason I run amsoil 100% synthetic in everything that I own with a motor, of all the oils I looked at, amsoil has the ability to suspend the highest percentage of water in solution at all temps below 212 degrees F, at which point the oil looses the water to vapor. This reduces sludge, wear, and the oil can also better deal with the condensation and acids therein at cold start. Everything gets a fresh dose of oil in the spring and filter replacements based on mileage throughout the year. I have not had an oil related problem with any of my cars or equipment since I started using this practice, what else can I say.