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V10 upgrade and decreased tire psi?

I just received my V10 upgrade on my Aug 2019 build LR AWD Model 3 and today I noticed that all of my tires are set to 42 psi. Prior to my upgrade my tires were set to 45 psi since delivery at the end of August even though my driver door panel says it should be 42 psi.. So, is it possible that there is some coding in the V10 release that automatically sets the Model 3's to 42 psi? Anyone else notice that with their car after the upgrade?
 
Your tire pressure is affected by the temperature outside.

So in late August, the temperature was in the high 70's? Now it's in the low 60's.
Yeah, I know the outside temps have an effect on the tires psi but just find it odd that a couple of days ago they were all 45 and today they are all exactly 42. So, I'm guessing it's no correlation to the recent upgrade. The temps in my area have pretty much been upper 80's to upper 90's the last few weeks. Today we have mid 70's during the day and low 50's overnight. In a month or two when it gets to the 30 and 40's should I expect my psi to drop a few more pounds or does it level off and maintain around 40-42 without me adjusting it?
 
The relationship between tire pressure and temperature is nearly linear, depending on the water content. So it will continue to drop as temperatures drop, and rise as temperature rises.

They could absolutely change the indicated pressure on the screen, but that wouldn't make a lot of sense to lie about the pressure.
 
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Reactions: NuttyM3
Isn't the temp relationship 1lb for every 10deg F?

Is it possible the firmware upgrade reset your TPMS?
I never thought of that but I guess it's a possibility. Oh, and with the decrease to 42 psi I can definitely tell the difference in the overall ride. It is smoother and unless it's just me the car is not as "road noisy" either. I still love driving it either way but the recent change seems like a good improvement.
 
I expect it to be a software thing.
Some TMPS compensate for temperature.
Then the little tmps- computer in car calculates the pressure back to 65 or 68 degr F.
Mayby with the update, that has chanched.
Did you read the 45 psi ( much to high to my opinion) on your screen or on the pressure device when filling?
 
I expect it to be a software thing.
Some TMPS compensate for temperature.
Then the little tmps- computer in car calculates the pressure back to 65 or 68 degr F.
Mayby with the update, that has chanched.
Did you read the 45 psi ( much to high to my opinion) on your screen or on the pressure device when filling?
I did verify the 45 psi reading on the car display screen with my tire pressure gauge and it was spot on. Now, I haven't checked the tires with the tire pressure gauge since the car screen readings went to 42 psi. I will need to do that to see if it maintains the same readout.
 
The relationship between tire pressure and temperature is nearly linear, depending on the water content. So it will continue to drop as temperatures drop, and rise as temperature rises.

They could absolutely change the indicated pressure on the screen, but that wouldn't make a lot of sense to lie about the pressure.

This is true, but the confusing/misleading aspect of this statement is that it is linear with *absolute* temperature (i.e., degrees Rankine or degrees Kelvin, vs. Fahrenheit or Celsius).

This means that going from 10 degrees Fahrenheit to 20 degrees Fahrenheit doesn't double the tire pressure, it just increases it by about 2%.

This is because absolute zero is actually -459.67 degreees Fahrenheit. So the actual temperature change on an absolute scale (rounded) is from 470 degrees Rankine to 480 degrees Rankine, or an approximately 2% change. (Note that 2% is fairly close to 1PSI at a pressure of 45PSI, so the rule of thumb that KenC mentions is not far off).
 
This is true, but the confusing/misleading aspect of this statement is that it is linear with *absolute* temperature (i.e., degrees Rankine or degrees Kelvin, vs. Fahrenheit or Celsius).

This means that going from 10 degrees Fahrenheit to 20 degrees Fahrenheit doesn't double the tire pressure, it just increases it by about 2%.

This is because absolute zero is actually -459.67 degreees Fahrenheit. So the actual temperature change on an absolute scale (rounded) is from 470 degrees Rankine to 480 degrees Rankine, or an approximately 2% change. (Note that 2% is fairly close to 1PSI at a pressure of 45PSI, so the rule of thumb that KenC mentions is not far off).

Then you forget that the pressure in tire is 14,7 psi higher then the outside air, so first add that before you calculate lineair from absolute zero temp ( - 459.67) , the n afterward substact the 14.7 psi again.
Doing that , might give that 1psi/10degrF. Rule of tumb.
Better would be a percentage of cold pressure for every 10degrF. Added a list I made with Excell. In this you see the 1psi/10degrF goes exact for 38 psi cold at 65 degr F.
 

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