(Assuming atmospheric pressure is 14.696 psi, or 101.3 kPA. 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 Using a tyre pressure chart can be a useful way of converting measurements. 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. 1kPa 0.14504Psi The pressure p in psi (Psi) is equal to the pressure p in kilopascal (kPa) times 0.14504, that conversion formula: p (Psi) p (kPa) × 0. If the temperature varies 10% (i.e., by 30 kelvins ), the pressure varies 10%. Result : 230 Kilopascal 33.35868 Psi How to convert Kilopascal to Psi 1 kilopascal (kPa) is equal to 0.14504 psi (Psi). 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. Although the pascal is more frequently used in scientific research, the psi is most often used in day-to-day contexts.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. The PSI is the unit most commonly used for measuring tyre pressure, as well as gas pipeline pressure and various other pressure measurements. One psi is approximately equivalent to 6,895 pascals. It’s defined as the pressure resulting from one pound-force applied to a one-square-inch area. Convert pressure values from kPa units to psi pressure units using the following method: .76 Pascals (Pa) Pascals (Pa) psi value x 6894.76 Pa kPa value x 1000 Pa psi value kPa value x 0. You can view more details on each measurement unit: kPa or pound/square inch The SI derived unit for pressure is the pascal. PSI (Pound-force per square inch)Ī pound-force per square inch (PSI) is an imperial unit of pressure calculated based on avoirdupois units. We assume you are converting between kilopascal and pound/square inch. The bar has been specified by the International Bureau of Weights and Measures as a unit that authors are permitted to use, but it is not included in the list of units accepted for use with SI. 1 bar is equal to 0.987 atmospheres, which is the unit most commonly used as a reference of standard pressure.ĭespite being a metric unit of pressure, the ‘bar’ is not accepted by the International System of Units (SI), and is no longer used in certain fields. Pressures above 35-36 psi for SL tires and 41-42 psi for XL tires will not increase the load capacity of the tire. A ‘bar’ is a unit of pressure defined exactly as 100,000 pascals.
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