I have had my car serviced at the same place for almost 20 years. You see the help come and go, and a lot of the ‘kids’ nowadays have very little training in the basics. At least these ‘newbies’ are well-supervised at this place.
But they never get the tire pressures right. I checked the tires a couple days ago, and they’re all over the place for pressure. On the little car, a difference of 2 PSI really makes a difference in the way it handles. And the differences were 5 PSI in a couple of cases. It was enough that the TPMS system was triggered so I had to stop on my way to work and check air in a driving rainstorm.
When I was doing this for a living, speed and accuracy were of equal importance, since it’s related to safety. And WOW did we get a lecturing if we let a car go out with the tires unsafely inflated. Typically we’d be sentenced to work for the next couple of days with the inflation and gauge head in our pocket. That thing was big, weighed a couple of pounds and you constantly knew it was there. You usually only do THAT once…
Here’s how it’s supposed to be done.
With a little practice, you can check/reinflate a tire within three seconds.
- Stab the air chuck (the end of the hose) onto the valve, making a good (noise-free seal). The reading stick in the gauge will rise to show the amount of air in the tire. This is not the correct reading! Continue and you’ll see why.
- Give the tire a short shot of air. The gauge will drop and rise again. This is STILL not the correct reading! At this point the gauge is reading the air from the high pressure side of the hose and it will always read high.
- This is key! Press (tap) the air valve enough to make it hiss, dumping the high-pressure air from the supply, and dropping the reading stick into the gauge. Now when you release the air valve, and when the measuring stick rises again, THIS will be the correct reading. Tap the air valve twice and average the two readings. This is as close to perfect as you will get with one of these hose-end gauges.
The best thing if you want absolute perfection is to get a gauge from a motorcycle shop. They are expensive but very accurate and rugged.