Bmw X5 Owners Manual

My 01 BMW X5 owner's manual recommends that I have to use gasoline octane level. But is it really make a difference especially since I live in Denver, CO where the altitude is 5280ft above sea level I know that using higher octane high altitudereally doesnot make a difference . In addition to the price of gas is very expensive.

and the octane number of a motor to do with the compression ratio engine, so I'd say go with what the manual says

You can try using a lower octane and if you ping go higher, you will not hurt anything to try one or two tanks of low octane. I think you will find under way with the factory recommendation works best in this case. Going above that recommended is generally a waste of money though.

Your car has a "knock" sensor on it. If you get an engine light, yu'll not know why.