Had a question about this topic. My Mini Cooper requires 91+/premium fuel, which in my area equates to 93 octane. I'm not asking this out of cheapness or frugality, but I'm genuinely wondering: would 89 octane actually be BETTER to run in the winter than 93? To preface, my drive to work is roughly 2.5 miles. I drive there and back and then the car sits. So the engine is always cold when it gets driven. Given 30deg and below temperatures, I'm wondering if 89 will actually burn better than 93 under these conditions? I'm obviously not revving, racing, redlining the car on these commutes. The air is denser, which makes the air/fuel leaner. The air is colder, which resists knock better. Which of these factors "wins" out? Are there other factors aside from detergents in 93? I liken driving in the winter to running a cold air intake, in any case anything you use to cool the air/fuel lets u run leaner and produce more power - on the flip side, can you run a lower octane?