Tire pressure gauge question...

I have a Jegs round 15 lb tire gauge, and I need to know how it works.

Does it measure an absolute pressure, against a spring, for example, or does it measure the difference between ambient pressure and what it sees in the tire?

The reason I ask is because I live at some pretty big altitude. My shop is just under 7000 feet. If the gauge reads absolute, then when it shows 6lbs the tire is really seeing a difference of 9.5lbs from the ambient pressure (since our ambient is 3.5lbs less than sea level), so the tire will behave as if it had 9.5 lbs at sea level. If I want the tire to behave like it had 6lbs at sea level I would have to set it to be 2.5 here.

If, on the other hand, the gauge reads the delta between ambient pressure and what is in the tire, I would be OK setting it at 6 lbs.

Any help?

-Scouder

 

Tire pressure is a relative thing. Most guys vary it according to the race track. Maybe lower when the track is stickier or higher depending on what your car does. Essentially what that means is that the number isn't always the most important thing as long as the gauge reads consistently. On the other hand I was using that same 15$ moroso gauge and it read a whole lb less than other guys CSR gauges. I threw it away and bought a new gauge. I want something that reads the same as the other guy's. At least then I can double check it with a couple of other gauges. A good tire gauge is expensive and I wouldn't trust my Moroso gauge anymore. It lied to me for 6 months and we struggled to get down race tracks till I found it was a P.O.S. . Dave Germain

 

Dave:

He's asking how the gauge detects pressure and if changes in altitude (high and low atmospheric pressures) affects the reading of the tire gauge.

"Does it measure an absolute pressure, against a spring, for example, or does it measure the difference between ambient pressure and what it sees in the tire?"

Pressure is always going to a function of atmospheric pressure vs the pressure inside the tire. Higher altitudes will mean less air is required to reach a certain pressure because of lower atmospheric pressure on the outside of the tire, but that pressure will always measure the same. Setting the pressure with a reliable gauge will always have the same effect on the tire at any altitude and almost any guage, CSR or Moroso will remain constant, errors included. So the effect of 6 PSI set in a tire at Vail, Colorado, will be the same as 6 PSI set in a tire at Houston. However, if you set the tire at 6 PSI in Houston and take it to Vail, Colorado, without resetting it, it will read high because of the lower atmospheric pressure against the outside of the tire. If you set the tire at 6 PSI in Vail and take it to Houston without resetting it you may have a flat tire.

If you are curious, take the back off the gauge and look. I'm not sure about the Jegs gauge, but the CSR gauge uses a diaphram and they can be checked and recalibrated at NHRA national events.

RG

 

tire gauge

can anyone compare the CSI to the Buxtonenginering gauge? Thanks Don

 

Thanks Randy,

I'll pull the back and see if it's got a diaphram.

-Scouder