I feel "specialty" oils are a waste of money on this bike. The filtration system is very crude so you really need to change the oil and check/clean the filters often, like every thousand miles. An expensive synthetic oil that can run 10,000 miles does no good in this case, it's just a waste of money. I use any oil without the "Energy Conserving" endorsement. Those oils have additives that can make your clutch slip. Typically, only 30wt and below have that endorsement so I run 20-50 car oil. Many like the 15-40 diesel oil. I tried it but the 10 point thinner rating resulted in more top end noise so I went back to the 50.