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All cars will eventually lose air from their tires, whether driven or not. This article will explain why some tires lose air quicker than others, whether parked or driven regularly.

When a  vehicle is parked for an extended period, you might notice that the tires gradually lose air pressure or slowly deflate. This is because rubber is porous, and although it usually wouldn’t be enough to create a problem, air molecules will slowly leak through the rubber over time.

Why Do Tires Leak Air When Not Driven?

Porous Equalize Pressure

Air will find a way out of the tire in the end, whatever steps we take.

Tires will lose air regardless of whether your car is driven regularly, parked, and sitting on the wheels, up in the air on axle stands, or as a spare in the trunk of your car.

High pressure will always try and escape to lower pressure.

This is because rubber is a porous material, and air molecules – oxygen and hydrogen – will always find a way of escaping, even if the seal around the bead is perfect.

One strange fact about this is that air pressure of 15 to 20 psi drops less quickly than a tire with more standard 30 – 35 psi of air inside it.

This has to be due to the pressure difference between 35 psi and normal air pressure compared to a tire inflated at 15 psi, causing an inversion.

If your parked car is losing more air pressure than one or two psi per month, it could be escaping from the bead seal. The leak won’t improve until the tire is reseated at a tire shop.

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Rim Damage

Even the slightest distortion of the rim will cause the tire not to seat correctly and stop it from being airtight. Air will exploit it and find its way out if there is a flaw. Most rim damage won’t affect the tire’s ability to hold the pressure, but damage around the lip will cause a leak.

Tire Bead

Over time air will escape through tire beads. If the wheel and tire are in good condition, you can expect to lose half a psi per month, resulting in a drop of maybe six psi over a year. Anything more indicates that not enough sealer was applied to the tire when the technician fitted it or the rim is slightly bent.

Dry Rot

Car tires stored and not driven for long periods are more susceptible to dry rot. Although oil-based chemicals that contact the tire when on the road will cause early aging of a tire, the tire is far more susceptible to premature aging when stored in high temperatures in direct sunlight.

Dry what isn’t dry rot at all. Only trees can get dry rot. But it is a term often used to describe the brittleness you see on tires as they dry out.

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As noted, rubber is a porous material; eventually, air will find its way out. But the air can escape sooner if the tire is affected by dry rot.

Tire Flat Spotting

A train of thought says if a car is left in park for more than a month, the flat spot and the bottom of the tire will let air escape. This normally happens in hot climates, where the rubber becomes more pliable, but not exclusively.

Usually, a tire flat spot will remedy itself once the car is driven again. But if the tire has gone flat when stored on a car in hot conditions, it may be irreparable and needs to be replaced.

Therefore it is always worth driving the car backward and forwards slightly every couple of weeks to ensure the same part of the tire isn’t in contact with the ground all the time.

Valve Stem

Suppose you haven’t washed your wheels and tires before storing or parking your vehicle for an extended period. The chemicals on the road, especially in winter, might have started to erode the valve stem slightly.

In normal circumstances, as you drive your car, occasionally in the rain, this will wash away any debris, dirt, or chemicals that may accumulate around the tire and valve stem and prevent this from happening.

Tire Pressure When Parked or Jacked On Axles

If you take the pressure off stationary tires and put the wheels on stands or jack up on the axle, you’ll preserve your tires for longer. If you need the car regularly, this isn’t an option.

In summary

All tires will lose air pressure eventually, whether parked, jacked up, or driven regularly.

The factors that can affect how quickly air pressure is lost is

  • The quality of the rims.
  • How good the tire bead was sealed to the rim at the tire shop.
  • Whether the tire is starting to show signs of dry rot.
  • The tire has been moved backward and forward slightly to avoid flat spotting.
  • Whether the tire was washed if being stored for long periods.

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