Ford: “We do not recommend the use of gasolines labeled as “Regular” that are sold with octane ratings of 86 or lower in high altitude areas.”
Corolla Owner’s Manual instructs to use 87 octane or higher in our four-cylinder engine.
It does not discourage using 85 at high elevation. (Denver octane ratings: 85, 87, 91. Occasionally 89 is found.)
Would 85 octane be OK at Mile-High Denver?
Or is better performance and less fuel consumption (if any) worth the increased co$t?