Just as socks disappear in the washing machine, air always disappears from tires in the winter. Both are annoying!
Where did the air go?
Yesterday we went shopping in Strømstad. Among the things on the shopping list was Pepsi Max. When I found the bag of Swedish empty plastic bottles to return, I noticed something strange. All the bottles looked as if the air had been sucked out. I always screw the cap on empty bottles, and now there was a big vacuum in all the bottles.
These bottles were purchased this summer. After being emptied, they have been stored in an underground garage where the temperature fluctuates somewhat. I was amazed at how much they had shrunk, and that they were still shrunk after being brought to room temperature.
The same thing happens to the air in the tires when the temperature fluctuates. When the temperature drops significantly, the air pressure drops. When the air gets warmer, or cars enter a warm garage, the air pressure doesn't return.
The air pressure did not return
I took the car out of a warm garage (12 degrees), drove it up into the mountains one winter day and left it outside overnight (-18) while I monitored the tire pressure. The next day, the air pressure in all four tires had dropped 0.2 bar – one had fallen below the tire pressure warning limit. I neglected to top up. Once home in the garage, the air pressure rose slightly, but the air had to be topped up to get back to the same level.
A car that is left outside all day will gradually lose tire pressure as the temperature changes, but probably less than cars that are driven into a warm garage every night. With temperature changes of +-10 degrees every day during the winter months, the tires will experience the same as Pepsi Max bottles. This can cause the tire pressure warning to light up as often as every 3 weeks. Filling up with more air than prescribed may give longer intervals, but can also cause abnormal tire wear. I experienced this when I filled up 0.2 bar extra throughout the winter.
The message is that you need to check and top up your tires more often in winter than in summer. Check your tire pressure when your tires are cold.
Other sources of air loss
Not all rim and tire solutions withstand Norwegian winter roads equally well. I suspect that wheels with a short distance between the rim and the road surface may be prone to air loss due to salt and dirt in the transition between the tire and rim. Air loss can also be caused by a nail or screw getting into the tire. Last year I had to have a tire plugged because of a screw that had barely penetrated the tire. The air loss was barely noticeable.
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Interesting read, thanks for sharing your knowledge.