Air Pressure – Correct, Underinflated and Overinflated

Air Pressure – Correct, Underinflated and Overinflated

Advantages of Correct Tire Inflation

Maintaining correct tire inflation pressure helps optimize tire performance and fuel economy. Correct tire inflation pressure allows drivers to experience tire comfort, durability and performance designed to match the needs of their vehicles. Tire deflection (the tread and sidewall flexing where the tread comes into contact with the road) will remain as originally designed and excessive sidewall flexing and tread squirm will be avoided. Heat buildup will be managed and rolling resistance will be appropriate. Proper tire inflation pressure also stabilizes the tire’s structure, blending the tire’s responsiveness, traction and handling.

Disadvantages of Underinflation

An underinflated tire can’t maintain its shape and becomes flatter than intended while in contact with the road. If a vehicle’s tires are underinflated by only 6 psi it could lead to tire failure. Additionally, the tire’s tread life could be reduced by as much as 25%. Lower inflation pressure will allow the tire to deflect (bend) more as it rolls. This will build up internal heat, increase rolling resistance and cause a reduction in fuel economy of up to 5%. You would experience a significant loss of steering precision and cornering stability. While 6 psi doesn’t seem excessively low, remember, it usually represents about 20% of the tire’s recommended pressure.

Disadvantages of Overinflation

An overinflated tire is stiff and unyielding and the size of its footprint in contact with the road is reduced. If a vehicle’s tires are overinflated by 6 psi, they could be damaged more easily when running over potholes or debris in the road. Higher inflated tires cannot isolate road irregularities well, causing them to ride harsher. However, higher inflation pressures usually provide an improvement in steering response and cornering stability up to a point. This is why participants who use street tires in autocrosses, track events and road races run higher than normal inflation pressures. The pressure must be checked with a quality air gauge as the inflation pressure cannot be accurately estimated through visual inspection



Our Recommendations:

For normal street cars, we generally recommend following the manufacturers recommended pressures. Even if you upgrade your wheels and tires, these pressures are set for the car. This applies to all “proper” fitting wheel and tires packages. For custom applications, our recommendations would change. If you have a stretched tire setup, your should probably run more pressure, up to the maximum that is recommended for the tire. For track and race cars, we would typically recommend a goal of 37-38psi hot, which means you will start your session with approximately 32psi, this will vary between cars and environments. Accurate measurement is essential here. The pressures should be fine tuned based on handling feedback and tire wear patterns. For more information, feel free to contact us at the shop.


RRT Automotive is Northern Virginia's premier BMW, Porsche, Audi and Mercedes service, repair and performance facility.