Does ambient temperature affect tire pressure gauges?

Staff
By Staff Writer
Jun 23, 2022 | Tire Pressure, Pressure Gauge | Posted in Shop Work , News and Notes | From the Nov. 2009 issue | Never miss an article

[Editor's note: This article originally appeared in the November 2009 issue of Grassroots Motorsports.]

As we fine-tune our setups, we often make small tire pressure adjustments to help balance the car and manage tire wear. Small changes can make a difference, and the gap between winning and second place can be smaller still. So how accurate is your tire pressure gauge?

To find out how the various commercially available tire pressure gauges behave in real-world conditions, we tested several types against a calibrated, high-end digital unit. We used a tire and wheel assembly initially set at 40 psi, and took multiple samples with each gauge. Readings were taken back to back with the reference gauge to minimize the influence of air loss due to those multiple readings. The reference gauge and tire were kept in a climate-controlled room for consistency.

The Gauges

From left to right, our test subjects included a reasonably pricey enthusiast-grade dial gauge, an inexpensive gas station stick gauge, and high- and low-end consumer-grade digital gauges.

  • Reference: This high-end digital gauge has been calibrated for 1/10 psi accuracy.
  • $50 0-60 psi dial gauge w/bleeder valve: This gauge has been in service for several years, replacing one that was ruined by a single drop onto the pavement.
  • $18 low-cost digital gauge: We’ve used this one daily for nearly a year and have dropped and banged it a number of times.
  • $5 pocket digital gauge: This one’s brand-new.
  • $1 pencil-style stick gauge: This gauge has led an unknown but lengthy service life.

Room Temperature (72 Degrees F)

  • Dial gauge: 0.9 psi low, 2.26 percent error
  • Low-cost digital gauge: 0.4 psi high, 0.98 percent error
  • Pocket digital gauge: 6.4 psi high, 16.11 percent error
  • Pencil gauge: 5.6 psi low, 14.18 percent error

The low-cost digital gauge proved to be consistent and accurate despite its hard service life. The $50 dial gauge was also reasonably close, but it was off by more than 2 percent. Think all digital gauges are the same? The pocket digital gauge had a 6.4 psi error versus the reference—that’s 16 percent—along with a 2 psi variance in its readings. And since most pencil gauges are known to be inaccurate, our example’s 6 psi error wasn’t much of a surprise.

Below Freezing (4.5 Degrees F)

  • dial gauge: 2.0 psi low, 5.13 percent error
  • low-cost digital gauge: not functioning, no reading
  • pocket digital gauge: not functioning, no reading
  • pencil gauge: 4.8 psi low, 12.37 percent error

Have you ever left your gauge in a glovebox or unheated garage during cold winter months? Just as tire pressures change with temperature, so can the readings on your mechanical gauge. Why? Its pressure readings rely on a temperature-sensitive spring. 

To measure the effects of a chilly environment on our gauges, we stuck them in a freezer for 18 hours. At subzero temperatures, the dial gauge read 2 psi lower than the reference—that’s a 5 percent difference. Interestingly, the pencil gauge was slow to give its final reading, taking more than 2 seconds. Alarmingly, neither of the digital gauges worked. Their LED flashlights continued to function, so we knew their internal batteries still had some power.

In the Sun (105 Degrees F)

  • dial gauge: 0.8 psi low, 2.06 percent error
  • low-cost digital gauge: 0.2 psi high, 0.52 percent error
  • pocket digital gauge: never resumed functioning post- freeze, no reading
  • pencil gauge: 1.5 psi low, 3.9 percent error

After giving the gauges 24 hours to return to room temperature, we placed them in the sun for several hours. We wanted to simulate a gauge left on the pit wall or in a tool box. The air temperature was 79 degrees F, but the gauges heated up to 105 degrees.

Conclusions

Our tire gauge tests taught us a few things, and helped us come up with some recommendations for gathering the best readings possible:

  1. Treat your tire pressure gauge like the precision instrument it is.
  2. Go digital. Even $20 will buy an accurate gauge; spending more adds features and may allow for recalibration, but the bonus features probably won’t improve accuracy.
  3. Mechanical gauges are more prone to fluctuations in temperature. They can also be permanently damaged by even minor bangs and bumps.
  4. Always use the same pressure gauge, and take notes. Different gauges are likely to give different readings. Using the same gauge will at least keep all of your readings relative.
  5. Have your gauge regularly checked for accuracy.
  6. If your gauge reads low, you are over-inflating your tires. If your gauge reads high, you are unknowingly under-inflating your tires. 

And keep in mind: We conducted our test with our wheel and tire set to 40 psi. If your pressures are higher or lower, or if you’re using a different brand of gauge, your results are likely to be different. After all, even variance is variable.

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Comments
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Floating Doc (Forum Supporter)
Floating Doc (Forum Supporter) GRM+ Memberand PowerDork
4/30/22 7:04 a.m.

Hopefully this will get some replies with personal experiences. 

gunner (Forum Supporter)
gunner (Forum Supporter) GRM+ Memberand HalfDork
4/30/22 9:42 p.m.

One time at an autocross I was checking my tires to adjust them and another racer came over with a high end dial gauge and offered to show me how accurate it was. Of course I wanted him to show me, I'm always on the lookout for cool gadgets. The neat part was I had a digital gauge that was the twin to the low cost digital gauge tested here and the readings were identical between his gauge and mine.

livinon2wheels
livinon2wheels GRM+ Memberand New Reader
6/23/22 1:50 p.m.

Love the mechanical dial gauges but they are fragile. I have found digital gauges both fragile and unreliable. I hate battery powered anything when at remote locations like most autocross locations and many tracks. 

kb58
kb58 SuperDork
6/23/22 1:52 p.m.

Well the short answer is "yes", but the real question is, "by how much", which could/may vary widely between brands and measurement method.

J.A. Ackley
J.A. Ackley Senior Editor
6/23/22 2:21 p.m.

Also take care in selecting the right gauge for the right application. I encountered a successful oval-track racer who was struggling mightily. He then got faster. I found out later what went wrong.

He was using a tire pressure gauge intended for trucks rather than race cars, since his regular gauge broke. His pressures were way off. A gauge has a sweet spot for its accuracy. If you're looking to measure tires with pressures around 10psi, a truck gauge won't have anywhere close to the accuracy you need for that range.

MisterJA
MisterJA New Reader
6/24/22 7:56 p.m.

For HPDE days I use a dial gauge w/bleeder valve. After the first session I typically bleed off 6-8 psi of really hot air, probably near 180 F. Any idea how accurate the gauge is at that point? 

PT_SHO
PT_SHO New Reader
6/27/22 2:49 p.m.

In reply to MisterJA :

OOOooo, great question.  I was at Thunderhill for an autocross this weekend.  Afternoon conditions, air 105F, track surface 135+, tire tread surfaces 140+ after a couple of runs.  The air coming out as I was bleeding the tires made it uncomfortable to even be in the way of it!

So here's what you do.  Read off a tire that hasn't been run and is in the shade.  Then bleed off the tire you're interested in.  Then go back to the shade tire and take a reading of the "known" pressure.  If it changed much, there's your answer.  Extra credit: if it changed, then bleed a little, maybe 1/2 psi, through your gauge and see if it cools it enough to make a difference.  YMMV.

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