Re: Why do highly-rated shops overfill my tires?
One other thing to keep in mind is that most tire pressure gauges are very inaccurate. Having been a master distributor for Intercomp, I have tested a number of pressure gauges and have talked with their engineers on the topic. Dial and standard digital gauges can vary +/- 5 psi. These include ones used by tire shops and very seldom will two read the same. This is why professional racing teams use calibrated digital gauges that cost hundreds of dollars and read to a hundredth of a pound. Manufacturers recommend even those are returned once a year for recalibration. I happen to have one of these gauges and take it with me whenever I have tires mounted or rotated. You’d be amazed how inaccurate the gauges tire shops use are. I always tell the installer to over inflate my tires and then I bleed them down to where I want them as soon as they are mounted. With that all said, the gauge you keep in your car or toolbox may not be as accurate as you think or as accurate as the tire shop’s. Also remember there are a number of other factors that can cause tire pressures to fluctuate after they are mounted; the car sitting in the sun vs shade, and ambient temperature change(1 psi for every 10 degree change up or down). Jus food for thought.
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