Why does tire pressure decrease when a car is left unused for a long time?

[Thompson]

It is normal for tire pressure to decrease when a car is left unused for a long time. All tires require periodic inflation, especially those filled with air, as tire pressure fluctuates significantly with temperature changes. As long as the pressure doesn't drop rapidly within a short period, it is considered normal. Hazards of low tire pressure: Increased friction coefficient with the road surface, leading to higher fuel consumption; Causes heavy steering and potential alignment issues, compromising driving safety; Increases movement in various parts of the tire, leading to excessive rolling and abnormal heat generation; Reduces the functionality of the cord and rubber, potentially causing delamination or cord breakage, as well as excessive friction with the rim, resulting in damage to the tire bead and abnormal wear; Multiplies friction between the tire and the ground, causing a sharp rise in tire temperature, softening the tire, and drastically reducing its strength. This can lead to blowouts during high-speed driving; Increases tire deformation, making the tire sidewalls prone to cracking and inducing flexing movements, which generate excessive heat, accelerate rubber aging, fatigue the cord layers, and break the cords. It also enlarges the tire's contact area with the ground, speeding up shoulder wear.

[DiBryce]

As an automotive enthusiast, I've researched the reasons for tire pressure dropping after prolonged parking. The main cause is the slow permeation and leakage of air molecules through the microporous structure of tire rubber material, similar to a balloon slowly deflating. Additionally, temperature fluctuations can exacerbate gas expansion or contraction, leading to fluctuating pressure drops. Long-term vehicle inactivity can accelerate wear on the valve core seal, increasing air leakage, especially in older car models. Regular tire pressure checks are crucial—for example, inflating to the manufacturer's recommended value before parking and measuring monthly to prevent deformation, which also saves fuel and extends tire life. I keep a tire pressure gauge in my garage for convenient monitoring to avoid unnecessary troubles.