If live in the Colorado Rockie Mountains, where the altitude is above 8,000 feet then the highest octane the gas stations will sell is below 85 octane.
At sea level ca by 92 octane. But with the crappy ethanol - that stuff acts like you have water in your gas.
I had a 87 Honda Rebel and the state is trying to kill me by using ethanol - I had to put in octane booster AND gas dryer in it for every fill up. Or else I wouldn've died ten times over because when hit the gas to pull into traffic or go faster on the on ramp to the highway - The ethanol KILL the engine - and me along with it.
I hate ethanol..... Makes food prices higher, and takes more fuel to make it than it's supposed to save......... And deadly on a 1987 Honda Rebel 250cc.