Dear Car Talk:
My wife and daughter freak out when the tire pressure warning light comes on in their cars. I bought pumps that plug into what we used to call the cigarette lighter, but it’s just too complicated for them.
If the tire isn’t visibly low, is it OK to drive for a while until someone else can pump it back up? — Larry
Larry, if you had a roof leak, would you patch the roof, or try to find a bucket that your wife and daughter could empty more easily? I think you’re taking the wrong approach here. The real question is, Why do their tires keep losing air?
For most people, seeing the low tire pressure warning light is a rare occurrence. A tire in good working order shouldn’t lose any air at all or should lose it so slowly that the light comes on somewhere between once a year and never.
The problem with many low-pressure warning lights is that they don’t tell you a lot. They generally come on once the tire pressure falls about 10% below where it’s supposed to be. So, if your tire calls for 32 psi, for instance, and your pressure drops to 28, the light will come on. And at that point, you’re probably not in a lot of immediate danger.
But how fast is it dropping? Are you losing 1 psi per month? Or 1 psi per hour? The light won’t tell you that. And once the light is on, it can’t come on again to say “Hey, now you’re really low. I mean it, pull over!”
A visual inspection isn’t much use either. To the untrained eye, it can be hard to tell the difference between a tire that’s down 10% from a tire that’s down 30%. And the danger is that if you drive on a tire that’s under-filled, the tire can overheat. That’s particularly true if you’re driving at high speed and in hotter weather.
If the tire overheats, its inner structure can pull apart and cause a blowout, leading to a loss of control of the car and other unpleasant things. So, I generally recommend you address a low tire as soon as reasonably possible. Obviously, if it’s warm out and you’re driving at highway speed, you should act with much greater urgency.
But the bigger question for you, Larry, is, Why do these tires keep losing air? You could have a leak that’s caused by a flaw or nail hole in the tire itself, it could be a bad filler valve or it could be a problem with the rim, where the rubber of the tire meets the metal of the wheel.
If you’re losing air regularly, a tire shop can submerge each tire and find the leak and fix it for you. That’s the best solution, Larry. And you can finance the repair by selling those air pumps on eBay.
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