Join Date: Dec 2014
Location: Brisbane, QLD, Australia
The easy answer is to use an oil that meets the specified API rating, and also carries the JASO MA rating, as for viscosity, use the range that suits the climate as per the chart in the manual.
As we are dealing in multigrade oils only, then there are some benefits with synthetic based oil. They don't use viscosity index improvers in them, like mineral based oils do. Since it is these improvers that break down and cause loss of oil viscosity, then synthetics are a more viscosity stable oil.
The use of a good mineral based oil will provide very good performance. The key is to change oil as per schedule, or more often if you use the bike hard. In general, stick to a known good brand. A good mineral oil may well be better than a dodgy synthetic oil.
While on the subject of synthetic oils, we should be aware that in many countries, oil companies are allowed to sell their hydrocracked mineral oils under a synthetic oil. If you do really want a synthetic, it might be worthwhile doing some homework and finding out if the oil is a group 3 or group 4. Group 3 are hydrocracked mineral oils, while group 4 are proper synthetic oils.
In times gone by, we used to be able to use car oils with no drama. There was one documented study done on a Fireblade using GTX oil. It used this oil for 500'000klm, with very little loss of power. It was measured on a dyne at intervals during this time. These days, car oils are all about low friction and low fuel consumption. This is why we need to avoid them these days, or at least read their specs carefully. It has been the use of these oils that has seen a number of transmission failures in recent years.
Oh, and while I think of it, if you do lots of short trips, you will need to change your oil more often. The combustion process is just a very aggressive chemical reaction. In the air we have some oxygen. The fuel is a chain of hydrogen and carbon, and in some cases like E10 it will also have some oxygen in it too. Part of that normal combustion process is to bond some of the hydrogen and oxygen together, forming water. If we factor in some of the high sulphur contents in some fuels on the market, then we have H2OSO4 formed, or sulphuric acid, or battery acid if you like. This builds up in the crankcase. Oils have a buffer agent in their additive package to help protect against this, but when we do lots of short trips the water is never boiled out of the oil, and so it will build up to a level that the buffers won't be able to protect the engine components.