Far too often, I’m checking the tire pressures on a car and they are way overfilled. Most of the cars I work on specify tire pressures around 30-35 psi, and unless they’re low from a leak, they’re usually somewhere around there. But then sometimes I stick my gauge on the valve stem and it has way more air than it should.

My gauge is reading over 60 psi on this tire, which should have only about half that much. Whenever this happens, my guess is that the owner of the car saw the tire pressure light or thought the tires looked low, so they went to an inflation pump at a gas station, and just filled them until the looked full, rather than using a gauge to make sure they were putting in the correct amount. Tires on a car that’s sitting on the ground will never look full. The weight of the car will make the bottom of the tire bulge out a little bit. When a car’s weight is off the tire, it will be completely round, but you can’t use that to gauge whether the tire is properly filled. Always use a tire pressure gauge to ensure that you’re putting the correct amount of air in your tires.

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-Dan