Your brake rotors vs standing water 

Gas Mileage and Octane Basics!

- Check and adjust tire pressures at least once a month. The less air a tire has in it the more road friction it creates. More friction equals less gas mileage, not to mention more tire wear.

- Use the air conditioning instead of driving with open windows. Open windows disturb the areodynamics and create air resistance which in turn affects gas mileage.

- Use the best fuel possible. Your car will adjust to the fuel that you use regardless of octane level, (except when high level of Ethanol, over 10% which will affect running quality). However, you most likely are not saving any money when using 87 octane and here is why; assuming that you are using 87 octane fuel gives your vehicle a range of 300 miles during your normal weekly drive. Using 93 octane with the same driving habits may increase your range, let's say 360 miles. Basically, the lower octane requires more engine RPM to achieve the same vehicle speed. All things being equal, there is no point in taking a chance on the lower octane rated fuel.

- Lower your speed limit. Going from an average of 70 mph to 60mph can increase your gas mileage noticeably. The additional several minutes on the road is a good exchange.
 
- Ethanol Blends. Most gas stations sell fuel blended with 10% Ethanol. Customers inquire about the possibility of using alcohol fuels (e.g. E85) in BMW vehicles. No, your vehicle will not run on E85 at all, so do not use it. Most fuels, especially lower octane, have up to 10% Ethanol, which on its own should not pose a problem. The problem rises from the fact that Ethanol is Hydroscopic, (mixes with/absorbs water). As a result, ou could get fuel mixed with water which has the potential to cause engine or fuel system components damage. There is no way to tell and/or prevent this from happening, you can minimize the odds by filling up at busy gas stations and using high octane fuels.