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Discussion Starter · #1 ·
Just got a nice, new analog tire gauge. Tires all measured 30 PSI, but why does my TPMS read 30 Fs, but 32 Rs? Which one should I rely on?
 

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Discussion Starter · #3 ·
I would rely on the gauge over the TPMS. Is 30 psi what's recommended on your door jamb? Mine says 33. That said, when I fill my tires to 33psi using a digital gauge my TPMS will reflect the same value.
My GTS 4.0 door jam says 35 all around, but also says 30 all around for "Comfort Setting" or something like that terminology. I got it w/30 all around and haven't messed with it. Is there a reset I could do?
 

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So the other day I was out for a run in the country and noticed my tire pressures seemed to be a little high, so I stopped at a local park and my good old analog gauge wasn't registering so I just took a little out of the tires and tried to do the same all around. Back on the road, the pressures weren't that much lower so I decided after 20-something years I'd get a new tire gauge, digital this time. I've got an HPDE coming up this weekend and knew I'd need to check my air before the trip to the track and then track day adjustments. There's a good discussion on here on what gauges everyone likes, but I didn't have time to have the agreed best to ship, so I went with another one someone liked. I went to Auto Zone and bought a Slime 20017 digital. Now, I have to tell you that this old man doesn't like hovering over an analog gauge anymore and it was painless and easy to adjust all my 18" tires down to 29 psi. After doing that, I think I've fixed the old one, so it is coming along as a backup.
 

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Discussion Starter · #5 ·
Interesting, my battery went dead on my Michelin digital gauge, so I went back to an analog gauge again, with a great bleeder. Besides, the Michelin claimed to have a bleeder valve, but mine never worked! So, found in the Good to Know app this Comfort setting is only for cars that have the option in the MFD, and I don't believe mine does. I think only the GT4 has it. Will check again to confirm, but I'm pretty sure my GTS 4.0 doesn't have that option. If that's the case, then I'm running 5 lb lower than recommended. It also mentions in the app it's country dependent.
 

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Interesting, my battery went dead on my Michelin digital gauge, so I went back to an analog gauge again, with a great bleeder. Besides, the Michelin claimed to have a bleeder valve, but mine never worked! So, found in the Good to Know app this Comfort setting is only for cars that have the option in the MFD, and I don't believe mine does. I think only the GT4 has it. Will check again to confirm, but I'm pretty sure my GTS 4.0 doesn't have that option. If that's the case, then I'm running 5 lb lower than recommended. It also mentions in the app it's country dependent.
You should have the comfort setting (my car has it). Also, the comfort setting just lets the tpms know that you are running lower pressure so it lowers its threshold to give you a low pressure warning light. It does not affect the actual PSI readout that appears for each tire.
 

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While I have several very accurate pressure gauges, including ones that compensate for temperature, ultimately the only value that matters to owners is what the TPMS reports. So, I fill a tire to what my gauge says is the correct pressure, then I use an Autel scanner to read what the TPMS sensor reports, compute the delta and fill to what makes the TPMS report the correct pressure. I typically see anywhere from a 1 to 4 PSI difference between what my gauge reads vs. what the TPMS sensor reports. Calculating this difference is a pain, but less pain than having to visit a customer again to add a couple PSI!

So, I'd say you should figure out the average delta between what your gauge shows and what the TPMS system reads, and fill to make your TMPS happy. Unless you like looking at the orange warning light and dismissing alerts in the info center, that is…
 

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I'm sure that one gauge will give more consistent results than 4 in the TPMS.
Of course accuracy in the one gauge may be off. I had mine checked by 3 tyre shops and adjusted it for the average.
If I had one TPMS reading 4 lbs off I'd be asking for a warranty fix.
 

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Without doubt use a gauge for correct repeatable reading. It doesn’t have to be ‘super’ precise
I would guess that +/- 1 or even 2 would not be perceivable in normal use, what’s more important is that they are the same on the same axle etc.

TPMS is just an emergency facility to warn of a loss of air from those set as above to warn of a difference.
I often notice that if the right side is in the morning sun, the TPMS shows even a +2 psi over the left side but not as a warning just the numbers.
then down the road after a few miles it all evens up.

Not sure what the warning difference criteria is on TPMS, perhaps 5 psi🤔

So no, don’t use TPMS as a pressure setting tool IMHO.
 

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Discussion Starter · #10 ·
Without doubt use a gauge for correct repeatable reading. It doesn’t have to be ‘super’ precise
I would guess that +/- 1 or even 2 would not be perceivable in normal use, what’s more important is that they are the same on the same axle etc.

TPMS is just an emergency facility to warn of a loss of air from those set as above to warn of a difference.
I often notice that if the right side is in the morning sun, the TPMS shows even a +2 psi over the left side but not as a warning just the numbers.
then down the road after a few miles it all evens up.

Not sure what the warning difference criteria is on TPMS, perhaps 5 psi🤔

So no, don’t use TPMS as a pressure setting tool IMHO.
Right. I agree with you. TPMS is for monitoring rise or fall in pressure. I have always trusted my gauge for accuracy. Still need to see if my GTS 4.0 has a Comfort setting in the MFD. I honestly don't think it does, but I could've missed it. I do know the GT4 4.0 does.
 

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Discussion Starter · #11 ·
You should have the comfort setting (my car has it). Also, the comfort setting just lets the tpms know that you are running lower pressure so it lowers its threshold to give you a low pressure warning light. It does not affect the actual PSI readout that appears for each tire.
Turns out I do have a Comfort setting on the MFD. Was on the next page. It was already set there. The door jamb placard say 30 for Comfort Setting, 35 Regular. May split the difference, maybe I'll run 32, idk.
 

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Turns out I do have a Comfort setting on the MFD. Was on the next page. It was already set there. The door jamb placard say 30 for Comfort Setting, 35 Regular. May split the difference, maybe I'll run 32, idk.
IIRC there are some cautions/guidelines in the manual about Comfort Setting, including an increased likelihood of rim damage from pot holes.
 

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Just got a nice, new analog tire gauge. Tires all measured 30 PSI, but why does my TPMS read 30 Fs, but 32 Rs? Which one should I rely on?
Just finished my first HPDE last weekend. That sent TPMS into a tizzy and is still wrong, even though all tires are at 33 psi. Not sure how to reset. It's easy on my Audi A3. Any tips?
 

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I often notice that if the right side is in the morning sun, the TPMS shows even a +2 psi over the left side but not as a warning just the numbers.
then down the road after a few miles it all evens up.
...
Hah, never considered the sunny-side effect. I'll have to pay attention next time. Had one of the four tires 2psi higher recently. Maybe that was it.
 
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