You could have the best tires in the world on your vehicle, but it wouldn't matter if the air pressure inside them was less than perfect. Tire load capacity, durability, traction and handling go hand-in-hand with air pressure, so pull out that air gauge. Too little or too much pressure can negatively affect performance.
Most people assume that the tire itself determines air pressure, and while this holds some truth, most air pressure is determined by the vehicle itself. Yes, the vehicle—tires can fit a variety of different vehicles, but the vehicle manufacturer knows exactly what type of tire pressure will draw out the greatest performance. The psi branded on a tire's sidewall indicates the tire's maximum cold inflation pressure, but that maximum pressure might not be what your individual vehicle needs for maximum performance. So, when using your air gauge, you should always check your vehicle manufacturer's air pressure recommendation found in your owner's manual. (Read more.)
See all air gauges available at Tire Rack.
Most people assume that the tire itself determines air pressure, and while this holds some truth, most air pressure is determined by the vehicle itself. Yes, the vehicle—tires can fit a variety of different vehicles, but the vehicle manufacturer knows exactly what type of tire pressure will draw out the greatest performance. The psi branded on a tire's sidewall indicates the tire's maximum cold inflation pressure, but that maximum pressure might not be what your individual vehicle needs for maximum performance. So, when using your air gauge, you should always check your vehicle manufacturer's air pressure recommendation found in your owner's manual. (Read more.)
See all air gauges available at Tire Rack.

Depending on which 2004 Mustang model you have, our records indicate Ford recommends 30psi, 32psi or 35psi.
Depending on which tire you are using, the maximum cold inflation pressure could be 35psi, 44psi, 50psi or 51psi.
While higher inflation pressures will reduce tire rolling resistance, they will also reduce ride quality and the tire’s ability to absorb impact with potholes, driveways, curbs and debris on the road. This could possibly lead to road hazard damage or tire failure.
An increase of 7mpg simply due to using higher cold inflation pressures is beyond what the laboratory results indicate is possible, so we’ve got to believe you fine-tuned your driving style as well. Running the maximum cold inflation pressure branded on the tire sidewall is within the tire manufacturers’ specifications, however it is not a substitution for the vehicle’s recommendation.