Cold inflation pressure is the

inflation In economics, inflation is an increase in the average price of goods and services in terms of money. This increase is measured using a price index, typically a consumer price index (CPI). When the general price level rises, each unit of curre ...

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 eve ...

tire A tire (North American English) or tyre (Commonwealth English) is a ring-shaped component that surrounds a Rim (wheel), wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide Traction (engineeri ...

s as measured before a

car A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people rather than cargo. There are around one billio ...

is driven and the tires warmed up. Recommended cold inflation pressure is displayed in 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 peripheral ...

and on the Tire Information Placard attached to the vehicle door edge, pillar,

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. Cold inflation pressure is a gauge pressure and not an

absolute pressure Pressure measurement is the measurement of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in unit of measurement, units of force per unit of surface area. Many techniques have been developed for the me ...

. This article focuses on cold inflation pressures for passenger vehicles and trucks. The general principles are, of course, applicable to bicycle tires, tractor tires, and any other kind of tire with an internal structure that gives it a defined size and shape (as opposed to something that might resemble a very flexible balloon). A 2001 NHTSA study found that 40% of passenger cars have at least one tire under-inflated by or more. The number one cause of tire failure was determined to be under-inflation. Drivers are encouraged to make sure their tires are adequately inflated at all times. 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 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 or ψ), the twenty-third letter of the Greek alphabet * Psi (Cyrillic), letter of the early Cyrillic alphabet, adopted from Greek Arts and entertainment * "Psi" as an abbreviat ...

in the imperial and

US customary United States customary units form a system of measurement units commonly used in the United States and most U.S. territories since being standardized and adopted in 1832. The United States customary system developed from English units that ...

systems, bar, which is deprecated but accepted for use with SI, or the kilopascal (kPa), which is an SI unit.

Variation of tire pressure with temperature

Daily temperature fluctuations can result in appreciable changes in tire pressure. Cold inflation pressure should therefore be measured in the morning, as this is the coldest time of day. This will ensure a tire meets or exceeds the required inflation pressure at any time of day. Seasonal temperature fluctuations can also result in appreciable changes in tire pressure, and a tire that is properly inflated in the summer is likely to become underinflated in the winter. Because of this, it is important to check tire pressures whenever the local seasons change.

Variation of tire pressure with altitude

Atmospheric pressure will decrease around 0.5 psi for every 1000 feet above sea level. As a vehicle descends from a high altitude location, the absolute pressure inside the tire remains the same, but the atmospheric pressure increases; therefore the gauge pressure will decrease. Take for example a vehicle which had its cold inflation tire pressure set near Denver (altitude 5300 feet), and is descending towards Los Angeles (altitude 300 feet). The tires could become underinflated by as much as 2.5 psi. Cold inflation pressure should therefore be readjusted after any significant changes in altitude.

References

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

Variation of tire pressure with temperature

Variation of tire pressure with altitude

See also

References