Got this with a Google search.
"%
zinc is the amount of
zinc used as an extreme pressure, anti- wear additive. The
zinc is only used when there is actual metal to metal contact in the engine. Hopefully the
oil will do its job and this will rarely occur, but if it does, the zinc compounds react with the metal to prevent scuffing and wear. A level of .11% is enough to protect an automobile engine for the extended
oil drain interval, under normal use.
Those of you with high reving, air cooled motorcycles or turbo charged cars or bikes might want to look at the oils with the higher zinc content. More doesn't give you better protection, it gives you longer protection if the rate of metal to metal contact is abnormally high." Check out this website. It gives the zinc content of pretty much every
oil available.
http://www.micapeak.com/info/oiled.html From the chart the zinc content in Shell Rotella is .12%. I have always used Kendall GT-1 oil in my cars. The chart reads that the Kendall has a zinc content of .16%. Good stuff!
