A few months ago, I replaced tires on my Dodge Journey. One had a major flat, one had a leak, and the other two were low on their tread. While this tire change definitely kept me safer on the road, I noticed that no matter what I seemed to do as winter crept in I kept loosing air in my tires. Not a ton of air. Not anything that would lead me to go back to my tire guy, but small amounts as the weather got colder, but why? Did I have a slow leak? Did I have a bad valve stem? I didn’t think so, because the amount of air being lost wasn’t that big and seemed to go back up once the sun came back out and things warmed up a bit. After doing some research, here are a few reasons I’ve found as to why tires lose air in the winter.
It’s the Law – Charles’s Law
Anyone with a degree in chemistry can recite Charles’s law to you. This is also known as the law of volumes and what it basically boils down to is that the volume of a gas is directly proportional to its temperature. In its most basic form this means that gasses expand when they are heated and shrink when they cool. You can reliably expect a 1psi drop in pressure for every 10-degree Fahrenheit drop in temperature. A TPMS (Tire Pressure Monitoring System) can help you better monitor your tire pressure and takes out a lot of the guess work, but just because you get a warning light on a cold morning doesn’t mean you have a puncture. While it can be tempting to keep topping your car’s tires off during the winter months, be careful because once things warm up again your tire could blow if you don’t let some of the air out.
Air molecules are small, like really small, and they can naturally go through the larger ATOM structure of Rubber, not too fast, but you can reasonably expect to lose 1-3 psi per month just because of simple osmosis. The rate of loss depends a lot on the make and rubber style of your tire, so check your tires permeation rating to see if you are experiencing more loss than the tire should be. This permeation loss is the reason why mechanics and manufacturers recommend you check your tires pressure at least once a month just to see how much air your tire is losing.
Tire inflation is important. Properly inflated tires help keep you on the road, prevent skidding and sliding, and extend the life of your tires. Underinflated tires can cause a loss of control and even blowouts in the wrong circumstances. Check your pressure regularly and stay safe. Also, don’t be afraid to buy yourself an air compressor. You never know if you’ll need it while out on the road.