More realistically you would lower your gas mileage since the higher the octane, the harder it is for your car to ignite.
Hello Everyone, I just wanted to introduce myself. I have been watching these threads for over a year now, but decided to register now. I have an 89 325i that I can never seem to stop modifying. Located in Sunny Florida. I wanted to say that this quote is not exactly true. I'm not sure about worse gas mileage, but it ISN'T harder for your car to ignite. A higher octane fuel is more refined than a lower octane fuel, as lower fuels pre-ignite before the piston reaches dead top. Higher octane fuel resists this pre-ignition by only igniting near the top of the cylinder walls, driving the piston down with greater force than a lower fuel. Yes, it is true that some engines are designed to use lower octane fuel and would not benefit from anything else, but with higher mileage engines, I wouldn't feel comfortable having my pistons igniting at different times.