Cold inflation pressure is the inflation pressure of tires before a car is driven and the tires (tyres) warmed up. 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. Most passenger cars are recommended to have a tire pressure of 2.1 to 2.4 bars (210 to 240 kPa ; 30 to 35 psi ) when not warmed by driving. [1] A 2001 NHTSA study found that 40% of passenger cars have at least one tire under-inflated by 0.4 bars (6 psi) or more. [2] 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. 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.
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.
Ambient temperature affects the cold tire pressure. Cold tire absolute pressure (gauge pressure plus atmospheric pressure) varies directly with the absolute temperature, measured in kelvin.
From physics, the ideal gas law states that PV = nRT, where P is absolute pressure, T is absolute temperature, V is the volume, and nR is constant for a given number of molecules of gas. If the volume of the tire remains constant, a 1% increase in absolute temperature results in a 1% increase in absolute pressure.
As an example, a tire is inflated to 2.2 bar (220 kPa; 32 psi) at an ambient temperature of 300 K (27 °C; 80 °F). If the absolute temperature of the air in the tire increases by 1% to 303 K (30 °C; 86 °F), the absolute pressure also increases by 1%. The absolute pressure is the sum of the ambient atmospheric pressure (approximately 1.01 bars [101 kPa; 14.7 psi] at sea level) and the gauge pressure, giving a total of 3.21 bar (321 kPa; 46.6 psi). This 3 K (3.0 °C; 5.4 °F) increase results in a change of .0321 bar (3.21 kPa; 0.466 psi). However, a similar tire inflated at an ambient temperature of 250 K (−23 °C; −10 °F) only needs to be warmed up by 2.5 K (2.5 °C; 4.5 °F) to see the same 1% increase in pressure.
Due to the temperature-dependent pressure changes, seasonal temperature fluctuations can result in appreciable changes in tire pressure. [1]
(Assuming standard sea-level atmospheric pressure of 14.696 pounds per square inch or 101.33 kilopascals) [3]
Pressure at 20 °C (68 °F) | 10 psi | 20 psi | 30 psi | 40 psi | 50 psi | 60 psi | 70 psi | 80 psi | 90 psi | 100 psi | |
---|---|---|---|---|---|---|---|---|---|---|---|
104 °F | 11.7 psi | 22.4 psi | 33.1 psi | 43.7 psi | 54.4 psi | 65.1 psi | 75.8 psi | 86.5 psi | 97.1 psi | 107.8 psi | 40 °C |
86 °F | 10.8 psi | 21.2 psi | 31.5 psi | 41.9 psi | 52.2 psi | 62.5 psi | 72.9 psi | 83.2 psi | 93.6 psi | 103.9 psi | 30 °C |
68 °F | 10.0 psi | 20.0 psi | 30.0 psi | 40.0 psi | 50.0 psi | 60.0 psi | 70.0 psi | 80.0 psi | 90.0 psi | 100.0 psi | 20 °C |
50 °F | 9.2 psi | 18.8 psi | 28.5 psi | 38.1 psi | 47.8 psi | 57.5 psi | 67.1 psi | 76.8 psi | 86.4 psi | 96.1 psi | 10 °C |
32 °F | 8.3 psi | 17.6 psi | 26.9 psi | 36.3 psi | 45.6 psi | 54.9 psi | 64.2 psi | 73.5 psi | 82.9 psi | 92.2 psi | 0 °C |
14 °F | 7.5 psi | 16.4 psi | 25.4 psi | 34.4 psi | 43.4 psi | 52.4 psi | 61.3 psi | 70.3 psi | 79.3 psi | 88.3 psi | −10 °C |
−4 °F | 6.6 psi | 15.3 psi | 23.9 psi | 32.5 psi | 41.2 psi | 49.8 psi | 58.4 psi | 67.1 psi | 75.7 psi | 84.3 psi | −20°C |
−22°F | 5.8 psi | 14.1 psi | 22.4 psi | 30.7 psi | 39.0 psi | 47.3 psi | 55.5 psi | 63.8 psi | 72.1 psi | 80.4 psi | −30 °C |
−40 °F | 4.9 psi | 12.9 psi | 20.8 psi | 28.8 psi | 36.8 psi | 44.7 psi | 52.7 psi | 60.6 psi | 68.6 psi | 76.5 psi | −40 °C |
Pressure at 20 °C (68 °F) | 69 kPa | 138 kPa | 207 kPa | 276 kPa | 345 kPa | 414 kPa | 483 kPa | 551 kPa | 620 kPa | 689 kPa | |
104°F | 81 kPa | 154 kPa | 228 kPa | 301 kPa | 375 kPa | 449 kPa | 522 kPa | 596 kPa | 670 kPa | 743 kPa | 40 °C |
86 °F | 75 kPa | 146 kPa | 217 kPa | 289 kPa | 360 kPa | 431 kPa | 502 kPa | 574 kPa | 645 kPa | 716 kPa | 30 °C |
68 °F | 69 kPa | 138 kPa | 207 kPa | 276 kPa | 345 kPa | 414 kPa | 483 kPa | 551 kPa | 620 kPa | 689 kPa | 20°C |
50 °F | 63 kPa | 130 kPa | 196 kPa | 263 kPa | 329 kPa | 396 kPa | 463 kPa | 529 kPa | 596 kPa | 662 kPa | 10 °C |
32 °F | 57 kPa | 122 kPa | 186 kPa | 250 kPa | 314 kPa | 378 kPa | 443 kPa | 507 kPa | 571 kPa | 635 kPa | 0 °C |
14 °F | 52 kPa | 113 kPa | 175 kPa | 237 kPa | 299 kPa | 361 kPa | 423 kPa | 485 kPa | 546 kPa | 608 kPa | −10 °C |
−4 °F | 46 kPa | 105 kPa | 165 kPa | 224 kPa | 284 kPa | 343 kPa | 403 kPa | 462 kPa | 522 kPa | 581 kPa | −20 °C |
−22 °F | 40 kPa | 97 kPa | 154 kPa | 211 kPa | 269 kPa | 326 kPa | 383 kPa | 440 kPa | 497 kPa | 554 kPa | −30 °C |
−40 °F | 34 kPa | 89 kPa | 144 kPa | 199 kPa | 253 kPa | 308 kPa | 363 kPa | 418 kPa | 473 kPa | 527 kPa | −40 °C |
Pressure measurement is the measurement of an applied force by a fluid on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure mechanically are called pressure gauges,vacuum gauges or compound gauges. The widely used Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge.
Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the pressure relative to the ambient pressure.
Standard temperature and pressure (STP) are various standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and Technology (NIST), although these are not universally accepted standards. Other organizations have established a variety of alternative definitions for their standard reference conditions.
Atmospheric pressure, also known as air pressure or barometric pressure, is the pressure within the atmosphere of Earth. The standard atmosphere is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth; that is, the Earth's atmospheric pressure at sea level is approximately 1 atm.
A tire or tyre is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface over which the wheel travels. Most tires, such as those for automobiles and bicycles, are pneumatically inflated structures, which also provide a flexible cushion that absorbs shock as the tire rolls over rough features on the surface. Tires provide a footprint, called a contact patch, that is designed to match the weight of the vehicle with the bearing strength of the surface that it rolls over by providing a bearing pressure that will not deform the surface excessively.
The bar is a metric unit of pressure, but not part of the International System of Units (SI); it is defined as 100,000 Pa (100 kPa). A pressure of 1 bar is slightly less than the current average atmospheric pressure on Earth at sea level. By the barometric formula, 1 bar is roughly the atmospheric pressure on Earth at an altitude of 111 metres at 15 °C.
The Firestone and Ford tire controversy of the 1990s saw hundreds of people die in automobile crashes caused by the failure of Firestone tires installed on light trucks made by Ford Motor Company.
A tire-pressure gauge, or tyre-pressure gauge, is a pressure gauge used to measure the pressure of tires on a vehicle. Tire-pressure gauges can be used both professionally and casually and come in many different sizes.
ISO 5775 is an international standard for labeling the size of bicycle tires and rims. The system used was originally developed by the European Tyre and Rim Technical Organisation (ETRTO). It is designed to make tire sizing consistent and clear. It replaces overlapping informal systems that ambiguously distinguished between sizes. For example, at least 6 different "26 inch" sizes exist, and "27 inch" wheels have a larger diameter than American "28 inch" wheels. The Japanese Industrial Standards Committee also cooperates with ISO 5775. The corresponding Japanese standards are JIS D 9112 for tires and JIS D 9421 for rims.
The manifold absolute pressure sensor is one of the sensors used in an internal combustion engine's electronic control system.
Inch of mercury is a non-SI unit of measurement for pressure. It is used for barometric pressure in weather reports, refrigeration and aviation in the United States.
A standard cubic foot (scf) is a unit representing the amount of gas (such as natural gas) contained in a volume of one cubic foot at reference temperature and pressure conditions. It is the unit commonly used when following the customary system, a collection of standards set by the National Institute of Standards and Technology. Another unit used for the same purpose is the standard cubic metre (Sm3), derived from SI units, representing the amount of gas contained in a volume of one cubic meter at different reference conditions. The reference conditions depend on the type of gas and differ from other standard temperature and pressure conditions.
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Inspection and maintenance of tires is about inspecting for wear and damage on tires so that adjustments or measures can be made to take better care of the tires so that they last longer, or to detect or predict if repairs or replacement of the tires becomes necessary. Tire maintenance for motor vehicles is based on several factors. The chief reason for tire replacement is friction from moving contact with road surfaces, causing the tread on the outer perimeter of tires to eventually wear away. When the tread depth becomes too shallow, like for example below 3.2 mm, the tire is worn out and should be replaced. The same rims can usually be used throughout the lifetime of the car. Other problems encountered in tire maintenance include:
A bicycle tire is a tire that fits on the wheel of a bicycle or similar vehicle. These tires may also be used on tricycles, wheelchairs, and handcycles, frequently for racing. Bicycle tires provide an important source of suspension, generate the lateral forces necessary for balancing and turning, and generate the longitudinal forces necessary for propulsion and braking. Although the use of a pneumatic tire greatly reduces rolling resistance compared to the use of a rigid wheel or solid tire, the tires are still typically, the second largest source, after wind resistance, of power consumption on a level road. The modern detachable pneumatic bicycle tire contributed to the popularity and eventual dominance of the safety bicycle.
The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, in contact with the object.
The pound per square inch or, more accurately, pound-force per square inch, is a unit of measurement of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force with magnitude of one pound-force applied to an area of one square inch. In SI units, 1 psi is approximately 6,895 pascals.
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The metresea water (msw) is a metric unit of pressure used in underwater diving. It is defined as one tenth of a bar.