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Just wondering if using 91 octane and over is really that necessary?

Well, that really depends on your bike!

If the compression on your bike is high, and you use lower octane fuel, you run the risk of predetonation, or "Knocking". In a nutshell, octane actually makes the fuel 'less flammable.' So if you are running high compression ratios in your engine, and your fuel is 'too flammable' (octane too low) then the fuel may ignite before the spark plug sets it off.

This creates two flame fronts in your cylinder. (Combustion isn't an explosion per se ... it's more of a controlled burn) The first flame front is from predetonation, and the second flame front is created by your spark plug. The resulting reaction of two flame fronts in your cylinder could very easily blow a hole through your aluminum piston over time.

basically ... Just stick with what your manufacturer recommends

Unles your owners manual says so, I wouldn't. For example, my kz650 is a pretty low compression engine, so unless I advance my timing, I actually get worse performance and lower mileage with premium, along with rapid plug fouling at around town speeds. I have tested this thoroughly, and for my bike this is true. I run 87 octane. your bike may be higher compression. If you don't have a manual, maybe someone with the same bike will help you out. What bike is it?

I have a suzuki 650 savage, the manual recommends 91 or higher, i guess ill have to stick with that then, i was just hoping to save some money

Run the tank down to reserve, then put a gallon of 87 in it. See how it runs. If it pings badly, fill it the rest of the way with premium and stick with the good stuff. If not, you can save some coins at fuel stops. I suspect your Savage will handle the 87-89 stuff just fine, but.....

To me, saving 30 cents a fillup isn't worth risking a grand in engine damage. I can forego that latte a week to put the good stuff in my bike. But if you really want to pinch every penny, try what Buzzz said.

I'm a bit of a hypocrite in this area. My bike runs on anything and recommends 87, but I at least put 89 in it and fill up in the next county so I don't get the ethanol and additives in the gas. My car requires 91 octane minimum, and I've been running 87 in it for 91,000 trouble free miles. I tried a few tanks of 92/93, but the mileage was the same and the power output, as far as I could tell, was the same.

Octane that is higher arrests combustion at a lower temp. Pinging or pre-ignition is what it supposes to avoid. pre-ignition is a hot spot in your cylinder that ignites before the sparkplug can do its job of igniting the fuel (called the charge). Not all car or bikes benefit from higher octane, and as a matter of fact, some might run better on lower octane.

The Buzz test is a very valid one and a good way to save money where the manufacture might be covering their butt.

Great topic, I have moved it to the Total Motorcycle Garage (-= Everything Else =-) for all to read and to add their views on.

Mike.