It's that time of year again.....check tire pressure.


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It's that time of year again.....check tire pressure.

This week, a strong Arctic cold front moved across much of the U.S., plunging many areas into record-cold temperatures (and snowfall) for the date. Just one more classic reminder of the annual Change of Seasons.....and, all else equal, as the air temperature drops, so does your average tire pressures, which rise or fall (roughly) 1 PSI for each 10 degrees in air temperature. That, of course, can make a real difference in places like Denver, which went from the 80s to below freezing and snow in a matter of a few hours. But, of course, many other factors can affect PSIs as well. Tires, being black in color, absorb most of the sun's ultraviolet rays, so tires exposed to the sum can heat up significantly compared to tires that aren't. This explains why, sometimes, tires on one side of the car, facing the sun for awhile, will be a couple of PSI higher than those on the opposite side, in the shade (or a front/rear difference). Tires will also warm up from the friction of rolling on the road surface as you start to drive the vehicle....and, in some cases, from proximity to engine/transmission heat....I notice that in my FWD Buicks, where the fronts will sometimes heat up before the rears. Heat, of course, adds PSIs. Too-low PSIs will make the problem worse, because overly-soft tires will make even more heat...that was a classic problem with the old Explorer Ford/Firestone conflict in the recommended PSI.

All American-market vehicles, for their original factory-mounted wheels/tires (and which is probably the case in many other countries, too) have an official PSI recommendation for the vehicle. That can usually be found on a label or plaque on the driver's lower-door jamb (the door must be open to view it)...or, if not, under the hood somewhere on a label/plaque, inside the glove-compartment (or what passes for some glove compartments nowadays LOL), or in the Owners Manual. And, needless to say, in most cases, it is the day-to-day responsibility of the vehicle's owner to maintain the correct tire pressures, not Smiling Sam the Service-Advisor at the dealership, although, of course, they often check or adjust them during routine things like oil changes and periods inspections. But the dealership can't precisely set the PSIs under all conditions...the tires will often be warmer, at the dealership, after driving for awhile (or sitting in the sun), than they are cold. And that's important, because the a cold tire is defined as sitting of three hours or more, out of the sun. The recommended PSIs on the vehicle-label itself will be for a cold tire, not warm.

Some gas stations have free air pumps....others charge you for them with coin or bill-operated machines. I have a free air pump at the Shell station nearest my house, and, for emergencies, carry a small portable air-compressor in my trunk, which plugs into the vehicle's power outlet....they can be useful for helping out other people in a pinch, too.

All new American-market vehicles built in the last several years have a Federally mandated tire-pressure-monitoring device that warns of low pressure.....but the specifics and details of the system is not regulated. So, the hardware and readouts that you actually get depend on the bean-counters who design the vehicle, and how much money that they (and management) allow to be spend on it. Some systems, like on the Mazda6 I recently test-drove, use cheaper sensors and integration methods that warn when one or more tire is low, but only do it by comparing the straight-line rotation speeds of one or more wheels compared to the others (outer tires naturally roll faster on curves than the inner tires). If one tire is significantly or continually rolling faster than the others (a sign of low pressure and smaller diameter), a warning light will flash, and you must stop the vehicle, get out, and try and determine which tire is the culprit. (one more reason to carry a good-quality tire gauge with you). Other vehicles, like Buicks and other GM products, use a better (IMO) system that continually monitors the exact pressure in each tire.....all four PSIs are continually displayed in the dash-readout. I keep that readout on display at all times as I drive, so I can spot a significant drop in a tire before the warning-light in the cheaper system would go off. If there is an extreme drop in PSI the dash-display system, of course, even if you aren't monitoring the display, an emergency message will appear when the tire is down to 10 PSI or so....that actually happened once on my former Buick Verano. (I had to replace the had picked up major damage). But you can't necessarily depend on even the more sophisticated system after it has been sitting really needs to have the vehicle moving to give you accurate readings. And you can't always depend on the classic bulge in the lower part of the tire to warn you of low pressure.....the lower the tire-profile, the less of a bulge you will have to visually see low pressure. (one more, of many reasons, why I don't like low-profiles).

So, after my (often long-winded) ramblings...the basic moral is: All else equal, lower temperatures = lower PSIs. Simply keep an eye on them, and add air as needed.