What does PSI mean? PSI, in relation to tire pressure, stands for pounds per square inch. PSI is a unit of measurement for the pressure within a vacuum system, such as tire inflation or engine compression levels. A tire’s maximum inflation pressure is the highest cold inflation pressure that the tire is designed to hold. It is important to remember that the tire pressure should be checked and changed when the tire is cold. Cold can be defined as conditions that are early in the morning before the days ambient temperature, suns heat or any heat generated from the tire being used (driven). It is very important to routinely check the air pressure of tires to ensure they are within the recommended manufacturer’s PSI range.
What affect does climate have on tire pressure, more specifically, what does a cold/winter climate do to your tires? As your tires spin and warm up, the air inside of them expands. If the PSI is too high (an over inflated tire), it could cause the expansion to burst the tire. Several vehicle manufacturer’s owner’s manuals recommend operating winter tires several PSI (typically 3-5) higher than their recommended pressures for summer and all-season tires.
If the tire is designated as a “winter tire,” it usually features more aggressive tread designs, softer tread compounds and are often molded with deeper beginning tread depths than summer or all-season tires. While the combination of these design elements allow winter tires to remain more pliable in sub-freezing temperatures to provide more traction in snow and on ice, it often results in tires that have somewhat reduced responsiveness to driver input. The 3-5 psi higher recommended inflation pressures increase tire stability and help offset the reduction in responsiveness.
Additionally ambient air temperatures in winter typically range 40- to 50-degrees Fahrenheit colder than typical summer temperatures for the same location. The lower ambient temperatures allow tires to be more efficient at radiating heat and the tires will run cooler, building up less hot tire pressure. In this case, the 3-5 psi higher recommended inflation pressure increase helps offset the reduced hot tire pressures resulting from less heat buildup.
And finally, all tire pressures are intended to be measured cold, which means when the tires are at the same temperature as the air outside. Unfortunately, unless you park your vehicle outside or in an unheated, detached garage, and measure its tire pressures first thing on dark, cold mornings, the influence of attached garages or higher ambient air temperatures later in the day often means that drivers are actually measuring tires that are not completely cold. In this case the 3-5 psi higher recommended inflation pressure increase helps offset the reduced tire pressures associated with the conditions in which the tire pressures are typically measured.
Correct tire pressure not only allows drivers to experience the tire comfort, durability and performance designed to match the needs of their vehicles, but also helps the tire to wear correctly, thus leading it’s life to the fullest extent.
*Technical information obtained from TireRack.com.