Cold inflation pressure is the tire pressure pressure before the car is moved and the tire warmed. The recommended cold inflation pressure is displayed in the owner's manual and on the plaque (or sticker) affixed to the door, pillars, glovebox door or fuel filler cover. Drivers are encouraged to make sure their tires are lifted enough, as non-optimal tire pressure can greatly reduce fuel economy, increase emissions, increase wear on the edges of the tire surface, and can lead to premature tire failures. Excessive pressure, on the other hand, can cause impact collisions, decreased braking performance, and cause uneven wear (ie, greater wear on the center of the tire surface).
The tire pressure is usually measured in psi in imperial systems and US custom systems, bars, which are not valid yet accepted for use with SI or kilopascal (kPa), which are SI units.
The ambient temperature affects the tire pressure. The absolute cold tire pressure (measuring pressure plus atmospheric pressure) varies directly with absolute temperature, measured in kelvin.
From physics, the ideal gas law states that PV = nRT where P is the absolute pressure, T is the absolute temperature (Kelvin), V is the volume (assumed to be relatively constant in the case of the tire), and nR is constant to be given a number of gas molecules. To understand this, assume the tire is filled when it is 300 kelvin (80 degrees Fahrenheit). If the temperature varies 10% (ie, with 30 kelvins [also 30 degrees Celsius or 54 degrees Fahrenheit]), the pressure varies by 10%. So if the tire is charged at 80F to 32 psi (or 47 psi absolute when we add atmospheric pressure), the change will be 4.7 psi for a change of 30 degrees Celsius, or 0.16 psi per degree Celsius or 0.1 psi per degree Fahrenheit or 1 psi for every 10 degrees Fahrenheit. Using SI units, it would be 1.1 kPa per kelvin.
Therefore, for tires that are charged up to 32 psi, the normally-made approach is within the range of normal atmospheric temperature and pressure: Tire pressure increases 1 psi for every 10 degrees Fahrenheit increase in temperature, or otherwise decreases 1 psi for every 10 degrees Fahrenheit decrease in temperature and in SI units, tire pressures increased by 1.1 kPa for each temperature rise of 1 degree Celsius, or vice versa 1.1 kPa for each drop of 1 degree Celsius temperature. For tires requiring inflation greater than 32psi, it may be easier to use Rule of Thumb from a 2% pressure change for a 10-degree Fahrenheit change. From the table below, one can see that this is only an estimate:
Video Cold inflation pressure
Variations of Tire Pressure with Temperature in Fahrenheit and Celsius *
* Assuming the atmospheric pressure is 14,696 psi or 101.3 kPA. This disclaimer needs to discuss how much water is in this air. I assume this table is for regular air in a garage or garage with certain water content. Many sources say that the increase in water content makes the pressure more varied. Many sources say that one benefit of nitrogen is to remove water and not just air, and then pressure variations will decrease. I can not find a reference for how much less. It would be better to have a table for air as above which states a% water content, and another table with 93% Nitrogen, with very low water content in the rest of the air. It would be good to see the difference here for comparison purposes. Shops that provide nitrogen for free with tire services seem to overestimate the benefits of nitrogen, in this case. https://www.edmunds.com/car-care/should-you-fill-your-cires-tires-with-nitrogen.html
Maps Cold inflation pressure
See also
- Direct TPMS
- Tire pressure gauge
- Tire pressure monitoring system
References
Source of the article : Wikipedia
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