Pump vs Tire Gauge vs TPMS

[kmcdonal]

This is a question I have long wondered about. Figured I would get the expertise of this group on it.

I have often seen a significant difference between the tire pressure as measured by my pumps vs my tire pressure gauges vs the TPMS. I am wondering which one to trust. Here is the data from this morning. All tires were cold:

• 38 PSI as measured by the TPMS
• 40 PSI as measured by 2 tire pressure gauges
• 42 PSI as measured by two pumps that have built in gauges

Which one do I trust or am I overthinking it? 4 PSI difference seems like a fair bit. Plus if I trust the pumps, the TPMS may start complaining that the tires are underinflated.

Thanks in advance for the feedback.

Sponsored

 

[WuffvonTrips]

Good question. I claim no expertise but have a look at this article-

https://motorwerksag.com/everything...em makes use of,the dashboard of your Porsche.

Maintaining Your Porsche’s TPMS
For your TPMS to work properly, it is vital to service it regularly. Even though your Porsche has this device, it is still a good idea to physically inspect the tires often. Check your tire pressure with a good quality tire pressure gauge and compare the pressure with the one indicated in the car manual.

The TPMS sensors are known to have a certain life expectancy and it is usually between 5-7 years of usage. If the sensors are worn out or you have observed constant problems with them, it may be time to replace them. When you are changing your tires or even when you are rotating them, ask the technician to clean the sensors and also check for any signs of damage.

 

[Jonathan S.]

Definitely not the indicator at the pump.

As a possible solution, I've been using this:
https://www.amazon.com/gp/product/B07JL8YB36/
I don't care about tenths of a psi, but it's nice for not wonder whether "40" is really 39.5, whereas the TPMS "38" might be 38.4, in which case the differential is about half what it might be appear to be.
The other nice little feature on that model is that you can overshoot the target, then press a little valve button to bleed out the air until you're spot-on where you want to be, without having to reposition the gauge.

 

[MrBlueSky]

A regular check with a quality/accurate pressure gauge is what I opt for. TPMS has never been accurate in any of my cars and the only real benefit is to warn of pressure loss in my opinion.

 

[SergeyIndy]

I will have to double check but my gauge and TPMS are always the same, however, if I would have a 2 psi difference, I would still trust the car as it may use a different algorithm to calculate the pressures to take into account other variables that a direct gauge is not. I do understand that TPMS sensors can go bad but usually one at a time, therefore, if one is an outlier then it is most likely bad and needs replacement.

I use this one that states it is certified and accurate: https://www.amazon.com/gp/product/B07S4LKTY2/

 

[kmcdonal]

Thanks for the feedback. The car is only 4 months old (2025 model) so the TPMS should be good. The two gauges that read 40 PSI are pretty similar to what @Jonathan S. suggested above.

 

[kmcdonal]

Thanks for the feedback. The car is only 4 months old (2025 model) so the TPMS should be good. The two gauges that read 40 PSI are pretty similar to what @Jonathan S. suggested above.

Also, just to clarify, the pumps are ones that I own. Now that cars don't have spare tires, I keep a small pump in the trunk in each of my cars in case I need to add air in the middle of nowhere. The pumps have digital monitors built in.

 

[Speuk]

I always go by my tyre pressure gauge it gave readings very close to the TPMS on my 4S CT. I've now got a MY2025 4S ST and the tyre pressure gauge and TPMS are both giving me the same readings.

Try forcing a remeasure in the car. Select a different tyre size or type then change back to the correct tyre settings and the TPMS will remeasure from scratch when you drive off.

 

[Tooney]

Most new tire pressure gauges are not accurate.

 

[kmcdonal]

Most new tire pressure gauges are not accurate.

Thanks. I am going to order one of the gauges that does well in his test and see what happens.

Doing a little more reading, I think one thing that could be playing a factor is that I am at 5,500 feet above sea level. It sounds like different gauges and TPMS are not perfect at altitude.

 

[Tooney]

Thanks. I am going to order one of the gauges that does well in his test and see what happens.

Doing a little more reading, I think one thing that could be playing a factor is that I am at 5,500 feet above sea level. It sounds like different gauges and TPMS are not perfect at altitude.

'A man with one gauge always knows what the tire pressure is. A man with two gauges is never sure.'

 

[Jonathan S.]

Love that video!
(Bonus points for how all three digital gauges I have just happen to have performed nearly perfectly in his test.)
Even though all of the testing was summarized in a single summary table at the end, his unpretentious and earnest presentation was worth watching in its entirety -- I'm going to start watching all his videos and buy the highest-performing products, even if I have no use for them!

 

[RAHRCR]

I check/adjust my pressures regularly and have consistently found that the TPMS is exactly accurate to the compressor I use.

 

[f1eng]

I have never expected the pressure gauges to be accurate on the 12V DIY pumps I have owned and never use them. I have used a pressure gauge for over 50 years but now correct to the Porsche display.

 

[thefunkygibbon]

apologies if this isnt the right place to ask this, but it feels like it is.
So my TPMS has been moaning on an off for the nearly 2 weeks since i've had the car. so i went to the local garage that has a air pump and filled it to 39 at front and 37 at back as per the documentation.
in the TMPS its telling me its 38 and 36. so i can understand that its maybe slightly off as per all the chat in this thread. but the issue i have now is that in the other part of TPMS where it tells you the deviation, its saying that there is -1, -2, -1, -2 differences... which I'm baffled about given that all the readings are effectivly around -1 from the "recommended"
does TPMS not recalibrate itself and therefore the deviations should all be 0? even if not, should it not all be -1? if the tpms is faulty then surely i'd see that in the actual pressure part of the page and see all of the tyres being different values of pressure?

Sponsored