![]() ![]() This added pressure does nothing for load capacity. Some tires list 44 psi and many higher speed tires will list 50-51 psi. The maximum allowed pressure listed on a tire's sidewall can be higher however. Light and Standard Load tires have a maximum capacity pressure rating of 35-36 psi and Extra load tires have a maximum capacity pressure rating of 41-42 psi. However, they have added load capacity above certain pressures. Passenger tires will be rated Light Load (LL), Standard Load (SL), or Extra Load (XL).Įxtra Load tires of the same size will typically have the same load capacity at the same pressure as the Standard Load tire. ![]() Too little air can wear the tires unevenly on the outer edges and will reduce the tires load capacity below the engineered level.Įach tire is rated with a load range, load index number, and max pressure rating. Too much air can wear the tires unevenly in the center and can create a wondering effect on the vehicle's handling. Tire load capacity is directly related to air pressure in the tires.Īs tire pressure goes up or down, so does the load capacity of the tire. The size and pressure have been engineered specifically by the manufacturer for correct load capacity and will typically render the best results for tire wear and ride quality. (Assuming atmospheric pressure is 14.696 psi, or 101.3 kPA.Listed inside the driver's side door jamb of your vehicle there will be the originally installed tire size, load rating, and tire pressure for the front and rear tires. Variation of tire pressure with temperature in Fahrenheit and Celsius For tires that need inflation greater than 32 psi it might be easier to use a Rule of Thumb of 2% pressure change for a change of 10 degrees Fahrenheit.įrom the table below, one can see that these are only approximations: In SI units, tire pressure increases 1.1 kPa for each 1 Celsius degree increase in temperature, or conversely decreases 1.1 kPa for each 1 Celsius degree decrease in temperature. Tire pressure increases 1 psi for each 10 Fahrenheit degree increase in temperature, or conversely decreases 1 psi for each 10 Fahrenheit degree decrease in temperature and ![]() Hence, for a tire filled to 32 psi, the approximation usually made is that within the range of normal atmospheric temperatures and pressures: So if the tire was filled at 80 ☏ to 32 psi (or 47 psi absolute when we add atmospheric pressure), the change would be 4.7 psi for this 30 Celsius degree change, or 0.16 psi per Celsius degree or 0.1 psi per Fahrenheit degree or 1 psi for every 10 Fahrenheit degrees. If the temperature varies 10% (i.e., by 30 kelvins ), the pressure varies 10%. To understand this, assume the tire was filled when it was 300 kelvin (approximately 27 degrees Celsius or 80 degrees Fahrenheit). Cold tire absolute pressure (gauge pressure plus atmospheric pressure) varies directly with the absolute temperature, measured in kelvin.įrom physics, the ideal gas law states that PV = nRT, where P is absolute pressure, T is absolute temperature, V is the volume (assumed to be relatively constant in the case of a tire), and nR is constant for a given number of molecules of gas. Tire pressure is commonly measured in psi in the imperial and US customary systems, bar, which is deprecated but accepted for use with SI or the kilopascal (kPa), which is an SI unit.Īmbient temperature affects the cold tire pressure. Excessive pressure, on the other hand, will lead to impact-breaks, decreased braking performance, and cause increased wear on the center part of the tread surface. Drivers are encouraged to make sure their tires are adequately inflated, as under inflated tires can greatly reduce fuel economy, increase emissions, cause increased wear on the edges of the tread surface, and can lead to overheating and premature failure of the tire. 40% of passenger cars have at least one tire under-inflated by 6 psi or more. Most passenger cars are recommended to have a tire pressure of 30 to 35 pounds per square inch when not warmed by driving. Recommended cold inflation pressure is displayed on the owner's manual and on the placard (or sticker) attached to the vehicle door edge, pillar, glovebox door or fuel filler flap. A tyre pressure gauge displaying bar (outside) and Pounds per square inch (inside)Ĭold inflation pressure is the inflation pressure of tires before a car is driven and the tires (tyres) warmed up. ![]()
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