This reply should be stickied to the front and everyone who asks the question forced to read it first! I've listened to the argument for years. The above is the best advice.wheelie_steve said:If you can hear pinging you have some major detonation issues. Most engine misfires (detonations, pinging) can not be heard. If you can physically hear the detonation, that sound is the equivalent to hitting the piston with a hammer. Believe it or not, in a spark ignition engine the burn process of the air/fuel mixture is actually a controlled burn NOT an explosion like most people refer to it. When you have detonation (aka Pinging) it is an actual explosion and not a conrolled burn like it is supposed to be. the lower the octane the fuel the more volatile it is, this means it will ignite easier. In a 4 cycles engine you have exactly that, 4 cycles. These cycles are intake, compression, power, and exhaust. Pinging occurrs at the end of the compression stroke. When an air/fuel mixture gets compressed the fuel and air atomize and ignite easier. In a high compression engine the air/fuel mixture is obviously compressed more than a lower compression engine. Therefore, when using a lower octane gas (More volatile) in a high compression engine the air/fuel mixture will rapidly explode instead of burn, this is what creates the detonation. Severe detonation can result in bent connecting rods, and holes burned through the top of the piston. High compression isn't the only factor that plays a role in what octane to use eventhough it is the biggest reason for detonation. It may also depend on Valve timing, ignition timing, RPM, etc. Higher octane fuel will decrase the chance of detonation, but will not give you more power or gas mileage. If the manual says use 87 you could most likely get away with it or you could play it safer and go with 89, or even go with 100 octane if you really wanted to. Anything that is higher octane than what is needed is just a waste of $$$. In a motorcycle it is not a huge deal because you do not use that much fuel. I would just use what the manual says unless you have your engine modified. Changine the fuel curve with a power commander (if fuel injected), changing the jetting of the carb, changing ignition or cam timing, etc. will change what octane you need. Especially ignition timing. Advanced ignition timing need higher octane fuel. As I have said, Just use what the manual recommends or higher (never lower octane). I doubt a major motorcycle manufacturer would mislead you because they wouldnt want broken bikes with engine problems going back to the dealer for warranty work.