It’s important to note, though, that all these pressure units are interconnected. There are certainly more pressure units out there, like atmospheres (ATM), millimeters of mercury (mmHg), and torr, but BAR, PSI, and KPA are our main players when it comes to tire pressure. In the tire pressure context, a typical car tire might be inflated to about 200 to 250 KPA. The pascal is the metric system’s way of measuring pressure (and yes, it’s named after the famous French mathematician and physicist Blaise Pascal). This unit might sound the most alien, but it’s really quite straightforward. Last but definitely not least, we have KPA, short for Kilopascal. Sounds high, right? But it’s necessary to carry all that weight! What Does KPA Mean? In the tire world, passenger car tires are typically inflated to between 30 and 35 PSI, while truck tires can go up to 100 PSI. The weight of that pound pressing on that square inch is 1 PSI. Picture a one-pound weight resting on a one-inch by one-inch square. “Pound-force” here refers to a unit of force, based on the weight of a pound. Next in line is PSI, which stands for Pound-force per Square Inch. Remember this: If we say a tire’s pressure is 2.0 BAR, it’s pretty darn inflated! What Does PSI Mean In Tires? One BAR is roughly equal to the atmospheric pressure at sea level, which is quite a bit of pressure! But when it comes to tires, we usually deal with fractions of a BAR. No, not the place where you might grab a drink after work, but something far more important for our tires! A bar, in our context, is a unit of pressure. What Does Bar Mean In Pressure?įirst up, let’s talk about BAR.
These are the big guys in the tire pressure world, and they’re essential for keeping our wheels spinning smoothly. We’re going to focus on three main units: BAR, PSI, and KPA. They might sound complicated at first, but trust me, once you understand what they stand for, they’re as easy as pie. Meteorologists and weather reporters worldwide often use this unit for convenience, since working in pascals would result in much larger values.ġ5 psi = 15 × 0.0689475729 bar = 1.Hey there, tire enthusiast! Let’s delve into the nitty-gritty world of pressure units. Millibars (symbol: mb) are also commonly used when referencing atmospheric air pressure, where atmospheric pressure equals 1013.25 mbar (101.325 kPa). The International Bureau of Weights and Measures has specified the bar as a unit that authors should have the freedom to use but has chosen not to include the bar in the list of non-SI units accepted for use with SI. The term "bar" comes from the Greek word "baros," which means weight.Ĭurrent use: Although the bar is a metric unit of pressure, it is not accepted within the International System of Units (SI) and is even deprecated within certain fields. History/origin: The unit, bar, was introduced by Vilhelm Bjerknes, a Norwegian meteorologist who founded modern weather forecasting. It is equal to 0.987 atmospheres (101,325 Pa), the unit often used as a reference of standard pressure. Barĭefinition: A bar (symbol: bar) is a metric unit of pressure that is defined as exactly 100,000 pascals (symbol: Pa). Although the pascal is more widely used in scientific contexts, psi is more often used in everyday contexts, particularly in countries like the United States as well as others under the US customary or imperial systems of units. As such, the prototype pound at the time was known as the avoirdupois wool pound.Ĭurrent use: The psi is fairly widely used to measure numerous pressures, such as tire pressure, scuba tank pressure, natural gas pipeline pressure, among others. The system is believed to have come into use in England around 1300 and was used in the international wool trade. It is based on the avoirdupois system, a system that uses weights in terms of the avoirdupois pound, which was standardized in 1959. History/origin: Pound-force per square inch is a unit that originated in the imperial and US customary systems of units. One psi is approximately 6,895 pascals (N/m 2). It is defined as the pressure that results when a force of one pound-force is applied to a one-square-inch area. Definition: A pound-force per square inch (symbol: psi) is an imperial and US customary unit of pressure based on avoirdupois units.
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