The recommended inflation pressures for tires are specified in pounds per square inch (psi) or kilopascals (kPa) as indicated on the vehicle tire placard, certification label or in the owner’s manual.
Never set tire inflation pressures below the recommended inflation pressure found on the vehicle tire placard, certification label or owner’s manual. Underinflation causes excessive heat build-up and internal structural damage that may lead to a tire failure, including tread/belt separation, even at a later date. Do not exceed the maximum inflation pressure shown on the tire sidewall. Over inflated tires (over the maximum molded on the tire sidewall) are more likely to be cut, punctured or damaged by sudden impact from hitting an obstacle, such as a pothole.
Proper Inflation is Critical
Inflation pressure enables a tire to support the load and to control the vehicle, therefore proper inflation is critical. With the right amount of inflation pressure, the vehicle and the tires will achieve their optimum performance. In addition to tire safety, this means your tires will wear longer and improve vehicle fuel consumption. Note that some vehicles may have different cold inflation pressures for tires on the front and rear axles.
Operating a vehicle with just one tire under inflated by 8 psi (56 kPa) can reduce the life of the tire by 9,000 miles and can increase the vehicle’s fuel consumption by 4%.
Tires driven even a short distance while underinflated may be damaged beyond repair. Running a tire underinflated is like running the vehicle’s engine without enough oil or coolant. It may seem to work fine for a time, but serious permanent damage has occurred. Adding oil or coolant won’t repair engine damage, and adding inflation pressure won’t fix tire damage. The tire will remain seriously damaged and can still fail, even after inflation pressure is corrected.
It is impossible to determine whether radial tires are properly inflated just by looking at them. You must use a tire gauge to properly check the inflation pressure. Motorists should have their own gauge and keep it in the vehicle.
Checking Tire Pressure
Check your tire inflation pressures, including the spare, at least once a month and before going on a long trip. Tire pressure should be measured when tires are cold – that is, they have not been driven on. Otherwise, your tires may have heated up, increasing the inflation pressure inside them by several pounds. This is normal. Never “bleed” or reduce the inflation pressure in a hot tire.
Remember that tires lose pressure when the air temperature gets colder (about 1 psi or 7kPa for every 10°F drop in temperature). Tires may also lose a certain amount of pressure due to their permeability (about 2 psi or 14 kPa per month).
Failure to maintain correct inflation pressure may result in rapid wear and uneven tread wear, improper vehicle handling and excessive heat buildup, which may result in tire failure. (Evidence of a continuous leak or repeated underinflation requires tire removal and expert inspection.)
Tire Pressure Monitoring Systems (TPMS)
It is still important to check inflation pressure at least once a month, even on vehicles that are equipped with a TPMS. Tire pressure monitoring systems are designed to be beneficial and accurate. However, a TPMS should not be solely relied on for inflation pressure maintenance since some systems may have limitations, such as:
- Lack of warning of low inflation pressure until one or more tires are as much as 25% below the vehicle manufacturer recommendations.
- May only detect inflation pressure differences between tires (in other words, if all tires are losing inflation pressure at the same rate, it is possible that the TPMS will not adequately warn of inflation pressure loss).
- May not warn of rapid inflation pressure loss in a single tire.
Underinflation (prior to a TPMS warning) is increasingly dangerous at high speeds, heavy vehicle loads, extended distances and at high ambient temperatures.
Tire Inflation with Nitrogen
One of the most important factors in tire care is maintaining proper inflation pressure, regardless of the inflation gas. Nitrogen is an inert (non-flammable) gas – basically, nothing more than dry air with the oxygen removed (air contains about 78% nitrogen). Nitrogen inflation does not harm tires nor does it affect the warranty.
Proper tire inflation, whether nitrogen or normal air, helps tires wear longer, saves fuel, and helps prevent accidents. Under inflation, regardless of the inflation gas, can make it harder to steer and stop your vehicle, result in loss of vehicle control, cause sudden tire destruction, and lead to serious injury or death. Nitrogen and air can be mixed in any and all proportions. Nitrogen filled tires can and should have air added whenever nitrogen is not readily available, to maintain proper inflation as specified by the vehicle manufacturer.