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I haven't heard of any stations systematically offering lower octane in their fuels at higher altitudes. This is a good thing as there are plenty of turbocharged engines that would maintain the same compression in the engine regardless of the altitude.
I suggest some of you guys go to places like Glacier National Park and see what your octane options are. Maybe if you stay on high volume roads like freeways you have more choices, but when you get on a 2 lane road/hiway, your choices are few. Your bike still runs OK.
For those who say a CV carbed bike suffers none at altitude, you will be surprised when it happens. Or disappointed. Or both.BTDT.
Not because of thinner air its actually lower pressure(atmospheric, less BMEP!). Along I-40 thru NM the places I stop at are 90 tops.:-)
As higher the field elevation, as lower the air density. A carburator engine has only one setting, the lack of air at high field elevations results in a richer (up to way too rich) air/gas mixture which causes the well known lack of power.