Ford Mustang Owner's Manual page 249

Comparisons With EPA Estimates
EPA fuel economy figures are obtained from
laboratory tests under simulated road conditions
and may not reflect the actual conditions you
experience or your style of driving. The EPA
fuel economy estimate is not a guarantee that
you will achieve the fuel economy shown.
The following decrease fuel economy:
Lack of regular, scheduled maintenance
Rapid acceleration and excessive speed
Driving with your foot on the brake
Sudden stops
Extended engine idling
Using speed control in hilly terrain
Extended use of the A/C, defroster, rear
window defroster and other accessories
Underinflated tires
Heavy loads
Aftermarket add-ons such as bike, ski or
luggage racks, bug deflectors, etc.
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