The main issues, according to Goodyear, seem to be handling and performance.
According to the tire maker, "tires inflated over the vehicle manufacturer-recommended inflation pressure:
- "Will be stiffer than the manufacturer intended, which can result in reduced ride comfort, due to less ability to absorb road irregularities, and (have) greater susceptibility to tire/suspension damage because of harder impacts with pot holes and hazards;
- "Will have a smaller contact patch with the road, meaning less traction; and
- "Can be prone to fast center line wear due to reduced deflection in the contact patch area."
Goodyear said the more a tire is overinflated, the more these conditions will be amplified. For example, a tire with a vehicle manufacturer-recommended inflation pressure of 30 psi will be 17 percent overinflated at 35 psi, a condition Goodyear described as "significant." At 42 psi, or plus 12 psi in this example, the tires would be 40 percent overinflated.
Asked why proper inflation is so important, the tire maker noted that it's the inflation pressure in the tire that supports the vehicle's load, and "both over- and underinflated tires can lead to issues of uneven wear, accelerated wear, increased susceptibility to impact damage and sub-optimized handling and stopping power."
Goodyear also noted that "because a given tire size might be fitted by various vehicle manufacturers on different cars — all with different loads and driving characteristics — the recommended tire inflation pressure for any specific car is specified by the vehicle manufacturer and always should be found on the car."
In fact, this information can be found in several places in the vehicle, Goodyear said, including the owner's manual, and/or on the label inside the driver's door-side jamb, or inside the glove box or on the inside of the fuel door.