To answer a question i have been asked many many times over the years. “Do i use a fully synthetic oil in my bike”. Ducati for example have have always recomended the use of Fully synthetic in their bikes whilst the Jap manufacturers suggest a Semi synthetic. Why? It is normally due to tollerances, at least for a while anyway. A semi synthetic oil will allow the engine to “run in” and if you change it regularly is perfect for most bikes. Triumph for example suggest a Semi until the bike reaches 12000 miles and then start using a fully synthetic. Unless you are racing it i would always suggest using a Semi in Jap bikes unless it is really big on miles. One thing a fully will do is stick to the metal parts even if you have not used the bike for some time, great in the winter of course, better for the first start up of the season. Oil manufactuers always stress that most engine wear happens at start up when the engine is cold.
Most manufacturers suggest you use a semi synthetic oil in your bike. Lets use a GSXR600 for example, a 10w40 semi changed every 3500-4000 miles. Why do oil manufacturers sell fully synthetic? If you use your bike for track days then a fully synthetic oil is a very good idea and it will be able to cope with the high temperatures and continue to offer the anti wear properties even at competition level performance. Another good use of fully synthetic oil is when you dont use you bike very much, it sticks to metal much better than a semi oil and will help prevent engine wear on start up if you have not used your bike for a few weeks. If you use your bike regularly on the road and change the oil at regular service intervals then a semi sythetic oil is perfect.