[Val Walkinshaw]

At 14k replaced stock GY with Michelin Pilot Sport 4S. After ~750 miles on them I'm noticing fluctuations in pressure compared to stock. I've measured my tires with 2 external pressure gauges to compare against the car.

As a test I put all tires at 35 on a 55 degree day.
- All measured values per the car when cold are 3-5 lower than what I've measured. (Cold the car read 29-30 when set at 34.)

- After warmed up the measured values per the car are 3-4 higher than what I've measured.(Warm the car read 36-38 when set at 34)

Hope this makes sense. I understand the compound is different with the 4S vs GY but how do I deal with this. Is this a calibration issue?

[HOJO]

Did you ever conduct this same test with the Goodyears. It not then you could have had similar variations. I’m not to sure how exact the tpms system is. My gauge and DIC reading are always off a couple points from one another

[Vtor_ZL1]

As long as difference is consistent, gauge can be off, calibrated ?


My PS4S will be 29 psi cold and warm up to 32-35 psi depending on ambient and how much work I asked them to do.


I can tell which side of the car was facing the sun - pressure read from TPMS is that accurate.

[TJay74]

There is no way to calibrate the TPMS sensors, they read what they read.

As far as the fluctuations in the pressure readings in regards to time of day and temps, that is normal. If you put 32psi in the tires as the door card calls for on a warm day and the next morning the temps drops down lower the psi in the tires will be lower as well, that is caused by the temperature differential.

You have to stay on the tire pressure when the temps go from cold to hot or hot to cold.

[Val Walkinshaw]

The GYs didn't fluctuate . On rare occasion 2 PSI. With a 30 degree temp change. Not just driving around town.

[arpad_m]

Hm, tire pressures with my PS4S set (285/35/20 rear, 255/40/20 front) don't fluctuate during street driving, warmed up pressure is 2-3 psi higher than cold. After cooling down to approx the same ambient temp, they measure the same as before.

I have a mechanical Jaco tire gauge and it also shows roughly the same pressures as the TPMS (+/-0.5 psi).

I'm surprised that your TPMS readouts vary so much compared to your gauges, since you say you double-checked this with 2 gauges, they are unlikely to both be off so much. Are the values in the car uniform across tires, or do you see a diff between fronts/rears or individually, too?

[Val Walkinshaw]

It varies between all tires. (Not in any direct sunlight) Sometimes the right front is off by two. Once it's been off by 5.

I'm checking with both an external analog and digital gauge.

[VinnAY]

Some TPMS will see multiple PSI variance than with a gauge, it's frustrating to see it out of whack with a gauge. If it's reading that far off you might be able to try the warranty angle perhaps?? Or replace them yourself.

[Val Walkinshaw]

Warranty. Dealer. Ugh.
I think I'll more or less ignore the TPMS readouts unless they are squeaking at me. I'll remain diligent with checking them manually. I wonder because of the compound difference between them and the GY and if that's why I'm noticing this. Maybe the PS4S are more reactive to temp fluctuations due to the expanding/contracting nature of the 2 different compounds.

[arpad_m]

Originally Posted by BlueUnicorn

Warranty. Dealer. Ugh.
I think I'll more or less ignore the TPMS readouts unless they are squeaking at me. I'll remain diligent with checking them manually. I wonder because of the compound difference between them and the GY and if that's why I'm noticing this. Maybe the PS4S are more reactive to temp fluctuations due to the expanding/contracting nature of the 2 different compounds.

That is an interesting and somewhat plausible thought, at least to me, a relative tire noob.

I did observe up to +/-2 psi variances temporarily between sides and even individual tires on the TPMS during drives, say, if I make many more hard right turns than left or vice versa, but over time these settle and equalize again. Usually by the time I'm back home in the garage, pressures are the same across all tires again, maybe off by 1 occasionally. (Switching to metric units, kPa in this case, adds higher and interesting precision, because the system displays no decimal points and numbers are almost 7 times higher in kPa.)

Also understand your reluctance to see the dealership, but bumper to bumper is there specifically to get you covered for minor niggles like potentially inaccurate TPMS sensors. Are you afraid they'll damage the car, lift it wrong or something?

[ctrlz]

I find the TPMS readings to be quite accurate compared to my digital pressure gauge. All are within 1-2 psi. I am not sure how the TPMS reporting works as far as rounding to whole numbers. So, is 34.4 reported as 34 or 35?

[TJay74]

Originally Posted by arpad_m

That is an interesting and somewhat plausible thought, at least to me, a relative tire noob.

I did observe up to +/-2 psi variances temporarily between sides and even individual tires on the TPMS during drives, say, if I make many more hard right turns than left or vice versa, but over time these settle and equalize again. Usually by the time I'm back home in the garage, pressures are the same across all tires again, maybe off by 1 occasionally. (Switching to metric units, kPa in this case, adds higher and interesting precision, because the system displays no decimal points and numbers are almost 7 times higher in kPa.)

Also understand your reluctance to see the dealership, but bumper to bumper is there specifically to get you covered for minor niggles like potentially inaccurate TPMS sensors. Are you afraid they'll damage the car, lift it wrong or something?

Do as you like, but the dealership wont replace the TPMS sensors just because someone says they dont like how accurate they are. They are nothing more than a fail safe due to the .Gov requiring them. They are never right at start up and take a bit of driving before they start to report correctly due to needing to wake up.

The 1st and primary way to check the tires is either with a quality mechanical gauge or a good electronic gauge. I use that 1st and foremost, the cars TPMS system is just a quick check and or backup to let me know if I have a low or going flat tire.

[Redlinez]

Mine fluctuate with temp no more or less than my Goodyears. I will say having low profile tires (30-40 series) it doesn't take much at all for it to happen. It only takes a nano second with shop air to add a few pounds.