Cold inflation pressure is the

inflation In economics, inflation is an increase in the general price level of goods and services in an economy. When the general price level rises, each unit of currency buys fewer goods and services; consequently, inflation corresponds to a reducti ...

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and ...

tire A tire (American English) or tyre (British English) 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 t ...

s before the

car A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded as ...

is driven and the tires(tyres) warmed up. Recommended cold inflation pressure is displayed on the

owner's manual An owner's manual (also called an instruction manual or a user guide) is an instructional book or booklet that is supplied with almost all technologically advanced consumer products such as vehicles, home appliances and computer peripherals. ...

and on the

placard A placard is a notice installed in a public place, like a small :wikt:card, card, Signage, sign, or :wikt:plaque, plaque. It can be attached to or hung from a vehicle or building to indicate information about the vehicle operator or contents of a ve ...

(or

sticker A sticker is a type of label: a piece of printed paper, plastic, vinyl, or other material with temporary or permanent pressure sensitive adhesive on one side. It can be used for decoration or for functional purposes, depending on the situation ...

) attached to the vehicle door edge,

pillar A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member. ...

glovebox A glovebox (or glove box) is a sealed container that is designed to allow one to manipulate objects where a separate atmosphere is desired. Built into the sides of the glovebox are gloves arranged in such a way that the user can place their hand ...

door or fuel filler flap. 40% of passenger cars have at least one tire under-inflated by 6 psi or more. 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 Psi, PSI or Ψ may refer to: Alphabetic letters * Psi (Greek) (Ψ, ψ), the 23rd letter of the Greek alphabet * Psi (Cyrillic) (Ѱ, ѱ), letter of the early Cyrillic alphabet, adopted from Greek Arts and entertainment * "Psi" as an abbreviatio ...

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 The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and ph ...

. From physics, the

ideal gas law The ideal gas law, also called the general gas equation, is the equation of state of a hypothetical ideal gas. It is a good approximation of the behavior of many gases under many conditions, although it has several limitations. It was first stat ...

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. To understand this, assume the tire was filled when it was 300 kelvin (approximately 27 degrees Celsius or 80 degrees Fahrenheit). If the temperature varies 10% (i.e., by 30 kelvins lso 30 degrees Celsius or 54 degrees Fahrenheit, the pressure varies 10%. So if the tire was filled at 80 °F 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. Using SI units, that would be 1.1 kPa/K. Hence, for a tire filled to 32 psi, the approximation usually made is that within the range of normal atmospheric temperatures and pressures: 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 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. 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. From the table below, one can see that these are only approximations:

Variation of tire pressure with temperature in Fahrenheit and Celsius

(Assuming atmospheric pressure is 14.696 psi, or 101.3 kPA.)

References

{{Tires, state=collapsed Tire inflation Pressure Motor vehicle maintenance

Variation of tire pressure with temperature in Fahrenheit and Celsius

See also

References