Thursday, April 15, 2021 Detailed Auto Topics
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Properly setting the air pressure in tires can improve performance and extend life. Two pounds per square inch (PSI) can have a noticeable effect. Something not often considered is the accuracy of the gauge being used. Many gauges can read off by up to ten percent or more.

laboratory certified test instrument to calibrate air gaugesAccuracy can be a relative term, so how close is "close enough?" Most experts agree that two pounds per square inch (PSI) change in pressure will change performance. In race cars as little as a quarter PSI is considered significant. I think most people would agree, the closer the better. (please click on images for closer view)

Using a laboratory calibrated tester, we checked several gauges. Most we checked were only capable of accuracy around 10% of their reading. Setting a tire to forty PSI meant actually having between thirty-eight and forty-two PSI. Worse, these were new gauges, which are at the peak of their accuracy.

Pencil tire gauges work with a calibrated springThere are multiple types of gauges on the market.

 Ironically the simple pencil type gauge seems more accurate than many of the other gauges we tested. It can be assumed the simple design gives less room for error. This gauge consist of a barrel fitted with a piston. Air pressure enters the chuck and pushes a piston down, against a calibrated spring. This also pushes a scale out where pressure can be read.

The pencil gauges we tested were most accurate in a narrow range.

This range was usually close to the middle of the scale. At lower and higher pressure accuracy fell off significantly. Finding a gauge where your tire pressure is near the center of the scale may help. For instance if your tires call for 35 PSI, look for a gauge that reads up to 70 PSI.

The Bourdon tube style pressure gauge.  Accurate if quality components are usedDial type gauges normally operate with a Bourdon tube. This is a curved copper tube attached to the indicator needle by links and gears. Air pressure causes the tube to expand and move the gauge needle. With such a complex arrangement, quality of the internal parts is imperative.

A very well built Bourdon tube gauge can give excellent results.

Unfortunately, even expensive tire gauges tend to use very cheap dial-gauges.

Purchasing a test-grade gauge and the cheap gauge in one of these units will give very good results. The problems are, the expense of buying the better test-grade gauge and durability. Test-grade gauges are expensive. They also tend to be very fragile and are easily knocked out of calibration.

The final gauge type is the digital gauge. These gauges depend entirely on the quality of their electronic load cell for accuracy.

Most digital gauges that we tested use very inexpensive imported components and were no more accurate than the dial gauges


The Accura tire inflator from PCL Air TechnologyThere are very high quality digital gauges available. These offer the highest degree of accuracy, durability and tend to be accurate over their entire range. These gauges are precision instruments and come at a much higher price. Plan on spending around $120.00 for a quality digital gauge.

Caring for a quality gauge

Aggie, the AGCO Automotive logo A quality tire pressure gauge should be treated like any other piece of precision equipment. It should always be stored in a dry and cool place.

Aggie, the AGCO Automotive logo Always keep caps on the stems of tires. Debris in the valve stem will be forced into the gauge and cause inaccuracy. Use the gauge to blow any debris from the stem opening before attaching.

Aggie, the AGCO Automotive logo Any gauge must have an air tight seal at the valve stem. Tire chucks come is a variety of styles. Pick one that gives the best seal with your tires.

Aggie, the AGCO Automotive logo Tire inflators combine the gauge with an air valve to add and remove air from the tire. These are well worth the cost and add greatly to the ease of use.

Aggie, the AGCO Automotive logo If you store a digital gauge for a long period, remove the battery(s).

A precision tool makes the job easier and last for years.  Quality is always less expensive, when considered over time.

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