Porsche and elementary math
10-03-2021, 07:20 PM
#2
I gave up trying to figure out how to set optimal tire pressures on the car. Have you read the manual? It's a total confusing mess with specific tire pressures for all the various carrera models, then for each model there are comfort and standard settings, then for each there are winter and summer tire pressures, then within each of those choices, you have to choose normal or loaded (as if anybody adjusts pressures when they carry a couple of passengers), then when you think you have it all figured out, they throw in the sunroof curve ball saying this setting either is or isn't if your car is equipped with a sunroof and aerokit. It's German engineering at its finest... stressing about tiny details that really doesn't matter but missing gigantic details like the fact that everybody in American needs a couple of easy to access garage door opener buttons that don't require a system boot up to work.
So, bottom line is, I just try to eyeball the pressures in a relative range after reading that cluster F of a manual and pump them up as needed.
So, bottom line is, I just try to eyeball the pressures in a relative range after reading that cluster F of a manual and pump them up as needed.
Last edited by AlterZgo; 10-03-2021 at 07:22 PM.
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10-03-2021, 10:00 PM
#3
Burning Brakes
Is it possible the deviations are corrected for temperature, ie. the RR tire was warmer than the others?
10-04-2021, 06:07 AM
#4
Burning Brakes
rounding differences. And I'm sure they are using SI units internally and converting to English units.
And temperature as noted above I would think.
And temperature as noted above I would think.
Last edited by breny4104; 10-04-2021 at 07:29 AM.
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10-04-2021, 08:39 AM
#5
RL Community Team
Rennlist Member
Rennlist Member
Do not rely on the app. The dash is typically very accurate. Use a digital tire gauge with tenths and you’ll be able to get them reporting the same. While driving, you will see variations with tire temperature, so don’t get too OCD about this stuff.
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Mikey K (10-05-2021)
10-04-2021, 09:48 AM
#6
Three Wheelin'
I think the OP is commenting on the fact that the left rear is 42 PSI and showing as 4 PSI over (so assuming 38 PSI is the target) and the right rear is showing 45 PSI but still 4 PSI over what should be the same 38 PSI target. So, one of these two "variances" is wrong. If A-4=38 and B-4=38, then A must equal B.
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riwu (10-04-2021)
10-04-2021, 10:24 AM
#7
Burning Brakes
^^^Thanks for the heads up. We are just trying to rationalize it as not a math error.
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10-04-2021, 10:52 AM
#8
Three Wheelin'
I get it, but I think we a jamming square pegs into round holes. The "+4" is pretty obviously a measure of the actual pressure over the target pressure. I am more inclined to believe this is a glitch as opposed to some undisclosed algorithm.
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breny4104 (10-04-2021)
10-05-2021, 07:31 AM
#9
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The system is smart. It takes into account the current temperature of each tire. It basically shows the deviation from the optimal pressure for each tire separately, i.e. how much you need to change the pressure of each tire for it to be on the recommended level. In the case of OP, if you lower the pressure 0,4 PSI for each rear tire, they will both then have the recommended pressure (whatever it is). Afterwards, the system may (and most likely will depending on the prevailing temperatures) still show that one tire has higher pressure the other but that is just because the other tire is currently warmer, which again makes the current pressure higher (and vice versa if the tires are cold). As long as the shown deviation is +/- 0,0 for each tire, the pressures are correct.
Last edited by TheGreatJ; 10-05-2021 at 07:34 AM.
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Mercuriell (10-06-2021)
10-05-2021, 11:11 AM
#11
Instructor
Thread Starter
The system is smart. It takes into account the current temperature of each tire. It basically shows the deviation from the optimal pressure for each tire separately, i.e. how much you need to change the pressure of each tire for it to be on the recommended level. In the case of OP, if you lower the pressure 0,4 PSI for each rear tire, they will both then have the recommended pressure (whatever it is). Afterwards, the system may (and most likely will depending on the prevailing temperatures) still show that one tire has higher pressure the other but that is just because the other tire is currently warmer, which again makes the current pressure higher (and vice versa if the tires are cold). As long as the shown deviation is +/- 0,0 for each tire, the pressures are correct.
Most car manuals just instruct you to pump air when tires are cold.
It's actually recommending 38 (or 41). I pumped it up for autocross.
10-05-2021, 11:50 AM
#13
Three Wheelin'
My understanding from the owner’s manual is that the pressure “difference” that is showed in the PCM and the Connected App is the variance between the current actual pressures and the pressures when the TPMS was last baselined. It is NOT the difference with theoretical “target” pressures. As others have stated, it also factors the temperature of the tires, meaning the number represents by how much the tire pressure needs to be adjusted by to achieve the set baseline pressure.
Last edited by CanAutM3; 10-05-2021 at 01:57 PM.
10-05-2021, 12:40 PM
#14
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I came up this thing on my own... Nope!
The 992 manual advices exactly what I wrote above (I guess I am a bit nerdy but I read through the manuals of the vehicles that I own). You can fill the tires based on the deviation shown on the instruments. I guess this feature makes life a tad easier when you don't have to make sure that the tires are cold first...Also, starting from 2021 or 2022 models, I believe, when you have the Sport Chrono package, the individual tire temperatures are also shown in the PCM. However, the pressure deviation functionality should work even if you don't have the temperatures shown there.
Last edited by TheGreatJ; 10-05-2021 at 12:50 PM.
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jfr0317 (10-05-2021)
10-05-2021, 09:19 PM
#15
I gave up trying to figure out how to set optimal tire pressures on the car. Have you read the manual? It's a total confusing mess with specific tire pressures for all the various carrera models, then for each model there are comfort and standard settings, then for each there are winter and summer tire pressures, then within each of those choices, you have to choose normal or loaded (as if anybody adjusts pressures when they carry a couple of passengers), then when you think you have it all figured out, they throw in the sunroof curve ball saying this setting either is or isn't if your car is equipped with a sunroof and aerokit. It's German engineering at its finest... stressing about tiny details that really doesn't matter but missing gigantic details like the fact that everybody in American needs a couple of easy to access garage door opener buttons that don't require a system boot up to work.
So, bottom line is, I just try to eyeball the pressures in a relative range after reading that cluster F of a manual and pump them up as needed.
So, bottom line is, I just try to eyeball the pressures in a relative range after reading that cluster F of a manual and pump them up as needed.