pglaves
#13338
It should be stated that oils like those with weights 20w50 can and are still being produced to meet the API SG/SH grades because there is virtually zero chance that this heavy weight of an oil will make it to a vehicle that has a catalytic converter. Lighter oils, those destined for use in cars, with weights of 5w15, 0w30, etc., will never have these anti wear additives which are needed for the older engines.
Motorcycle specific oils in weights 20w50 and 10w40, with API SG ratings can be bought at either Auto Zone or many O"reilly stores, and at some Walmart stores. 10W40 is in spec for a number of cars with cat cons, and let us not forget that many recent BMW motorcycles:
a. have catalytic converters
and
b. are specified to use 10w40 or 20w50 viscosities with SG ratings.