Tire Pressure Monitor Vs. Tire Shop Gauge Reading

[EasternSP]

I had my wheels rotated yesterday and in the process they checked the balance and air pressure.
They inflated them to 51PSI. When I left I checked the on screen pressure and it was reading 56PSI.
Which one would be correct?

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[UberNoob]

All gages need calibration after a while, I’d guess both was correct under the conditions. I’m no tire expert, but I’d guess pressure under load increases on the truck vs off? I’m thinking squeezing a bag of Doritos eventually it bursts open.

 

[Gigahorse]

Could be filled cold to 51, warmed up with driving to 56

 

[REM]

if you want the most accurate fill, you have to equalize before the sun even comes up if you don't garage keep. temperature and thermal mass makes that big of a difference.

in the hot summer months, I usually underinflate cold temps to about 48, and the PSI will climb to 53ish to 55 during a drive on a particularly hot day.

 

[EasternSP]

I knew I was forgetting to include a specific piece of information.
I checked the pressure on the service screen just a block or so from the tire shop. less than a minute from leaving the tire shop. Air temp was in the 50s so I don't think they heated up in that short a time.

 

[mrcarcrazy]

Third (known good) gauge is needed to be sure. But it’s entirely possible the tire shops gauge was incorrect. It’s even plausible that both are incorrect.

If it was me; I’d drop the pressure to 50 in the truck if I wasn’t interested in checking with a known good gauge.

 

[Tallgeese179]

As mentioned, just check them in the morning before the sun rises. Adjust them to 50 psi on a dedicated gauge and then see what it reads out on the truck's screen. Keep an eye on it and adjust when you have large temperature swings.

They will of course increase in pressure as you drive, when the temp rises, or when the sun is beating down on them. The recommend tire pressure is for "cold" state, which is generally interpreted as "morning, steady state, not driven recently".

Extreme use cases will require variation from the recommendation of course.

I have one of these in all of my cars. They tested well on Project Farm and are cheap. Seem to be accurate within +/- 0.2 psi from the 3 different style gauges I have.

https://a.co/d/04ubWH2z

 

[SlegMD]

Good ol’ manual gauge

AZ has been somewhat tricky as temps range from high 60 to 90, tire pressure is ranging 46 in morning to 52 in afternoon

 

[EasternSP]

The two guys workin on my wheels were using two different work stations. Each one had their own air hose with gauge. It seems odd that both gauges would be off exactly the same amount as all four tires were at 56psi.

 

[SlegMD]

They were 56 after the drive home? Or when picked up the truck?

 

[HaulingAss]

I knew I was forgetting to include a specific piece of information.
I checked the pressure on the service screen just a block or so from the tire shop. less than a minute from leaving the tire shop. Air temp was in the 50s so I don't think they heated up in that short a time.

The TPMS display will indicate it's reading a stored temperature. It will say, for example "an hour ago" or "5 minutes ago". If it doesn't indicate it's a stored reading, it's a current reading.

The two guys workin on my wheels were using two different work stations. Each one had their own air hose with gauge. It seems odd that both gauges would be off exactly the same amount as all four tires were at 56psi.

You haven't given us enough information to say one way or the other with any certainty.
But in this case I would bank on the four TPMS gauges being more accurate. Do you know what the chances are of four individual TPMS gauges all reading exactly 5 psi too high?

Check them first thing in the morning before driving with a stand-alone gauge and let us know what they read. Then drive 25 mph for one or two blocks (until the display indicates the TPMS is reading the current pressure) and let us know what the TPMS reads.

My experience is the TPMS gauges in each of my Cybertruck tires (including the winter wheel/tire set I purchased from Tesla) are the most accurate TPMS gauges I've ever seen. Not only do they all read exactly the same pressure after I've equalized all four tires by connecting them together with my 4-way hose setup, but the pressure readings also correspond exactly to the two best and newest tire gauges I have (one digital and one analogue). Our three Model 3 TPMS's are good, but not this good (they might have a one PSI variation when they all have equal pressure). My previous Mazda and the F-150 was not nearly as good. You could fill all tires to exactly the same pressures and the TPMS would vary by up to 2 PSI per tire.

Note that it's normal for pressures to vary quite a bit from tire to tire when one or more tires have had more sun exposure than the rest. This even happens on a cold sunny day.

 

[EasternSP]

As I indicated, I checked them just a couple blocks from the shop. I left the service page on as I drove just in case it hadn't updated. It was still reading the 56 when I got home, just a couple miles away.
I didn't check it again after that as I didn't go anywhere. Will check em today when I go out.

 

[mongo]

TPMS tracks to within 1 psi to my M12 Milwaukee inflator.

 

[EasternSP]

Went out today and checked the pressure just a 1/4 mile down the street. 54PSI in all four tires.

 

[mongo]

Went out today and checked the pressure just a 1/4 mile down the street. 54PSI in all four tires.

The shop may run their regulators a little high to speed inflation.

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