Tire Pressure Monitor (TPM) and Fill Status

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Dec 7, 2012 | 02:54 PM
  #1  
Does anyone understand how the "Tire Pressure" and "Fill Info" are supposed to relate to each other? Look at the pictures below, taken while parked (cold tires) about 10 seconds apart. (Ignore the German--I figured if the car is German, its language should be German, too )
- Tire pressure shows 35, 33 in front, 44, 41 in back.
- Fill info shows 1psi overfill for fronts and 1psi underfill for right rear.
- Full load and Comfort level are selected.
- I have 20" wheels and the temperature is 22.5ºC.
Now, page 263 lists for 20" wheels at 20ºC, full load & comfort pressure 31psi for the front and 40psi for the back.

Further, the manual says on page 105:

Quote:
[The "Tire pressure"] display is only for information.

Under no circumstances should the tire pressures be changed based on this display.
(Emphasis by me.) Accordingly, page 106 states:

Quote:
Use only the pressure values shown in the "Fill info" display in the "Tire pressure" main menu or from the corresponding tire pressure warning when correcting the tire pressure.
Now, if I subtract the values displayed in "Fill info" from the target values, I get actual tire pressure values of 32, 32 in front and 40, 39 in the back, which is quite a difference from what the "Tire pressure" display shows.

So, what's the point of the "Tire pressure" display? Is it just me or is this really a bit too complicated?

  

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Dec 7, 2012 | 03:00 PM
  #2  
On a related note, if you drive 50% alone, 30% with 2 kids in the back and 20% with the wife, do you select "full load" or "partial load"?

Sorry if this is a silly question.
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Dec 7, 2012 | 03:59 PM
  #3  
Quote: On a related note, if you drive 50% alone, 30% with 2 kids in the back and 20% with the wife, do you select "full load" or "partial load"?

Sorry if this is a silly question.
Depends on the weight of the kids

ChuckJ
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Dec 7, 2012 | 04:10 PM
  #4  
Quote: Depends on the weight of the kids
OKOK, I guess I was asking for that comment Assume regular kids (age 4-8, 35-50lbs). And before you follow up with the wife, assume 120lbs/25 years, like they all are
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Dec 7, 2012 | 10:06 PM
  #5  
i'm a single guy and 99% of the time i'm the only passenger and once in a while I have one more passenger. I suppose I need to untick FULL LOAD?

Quote: On a related note, if you drive 50% alone, 30% with 2 kids in the back and 20% with the wife, do you select "full load" or "partial load"?

Sorry if this is a silly question.
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Dec 7, 2012 | 10:14 PM
  #6  
Quote: i'm a single guy and 99% of the time i'm the only passenger and once in a while I have one more passenger. I suppose I need to untick FULL LOAD?
I'd guess so, unless "partial load" means "nobody, not even a driver"
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Dec 8, 2012 | 07:40 AM
  #7  
The TPMS is so unreliable I'd just stick to measuring and setting the pressures by hand and be done with it. Mine routinely shows +3psi over the actual pressures for each wheel.
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Dec 8, 2012 | 07:53 AM
  #8  
Quote: The TPMS is so unreliable I'd just stick to measuring and setting the pressures by hand and be done with it. Mine routinely shows +3psi over the actual pressures for each wheel.

I'm going to follow your suggestion, as I'm also seeing unreliable readings.
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