Weird Psi Issue

impactplayer · 07-08-2013, 07:26 PM

I started getting a TPMS malfunction in iDrive and it won't allow me to do a reset. I double checked my tire pressure this morning (when tires were cold) and three of the four tires had dropped to approximately 35 psi (from 39/41 F/R) in the last month or two. However, one tire (rear driver) was at 45 psi. This is an increase of 4 psi from what I filled it up at a month or two ago, and 9 psi higher than the other tires. Any clue what happened? I'm a little confused

VMRWheels · 07-09-2013, 12:01 PM

It's fairly normal to lose some pressure over time. You aren't losing it at a super alarming rate. Now, I don't know why your pressure would go up on one corner but go down on the other three. Could be that whatever you checked your pressure with was inaccurate (before, or even now).

If you think you have a slow slow leak from somewhere, the old soap and water method would show you exactly where.

N8N · 07-09-2013, 12:10 PM

Is the weather significantly warmer (as in, tens of degrees F warmer) than it was when you filled the tires? Alternately, had you been driving for a while when you checked the pressure in your tires? remember PV = nRT and what that basically means to you is that pressure scales linearly with temperature (expressed in absolute degrees, e.g. Kelvin) so a hotter tire with the same number of molecules in it as a colder tire will read more pressure. That does NOT mean that you should let air out if you check the pressures with the tires hot, just that you should check the pressure after the car has been sitting overnight for the most accurate readings/fill of your tires.

07-08-2013, 07:26 PM	#1
impactplayer Private 1 Rep 54 Posts Drives: '08 E90 Join Date: Jan 2012 Location: Texas iTrader: (0)	Weird Psi Issue I started getting a TPMS malfunction in iDrive and it won't allow me to do a reset. I double checked my tire pressure this morning (when tires were cold) and three of the four tires had dropped to approximately 35 psi (from 39/41 F/R) in the last month or two. However, one tire (rear driver) was at 45 psi. This is an increase of 4 psi from what I filled it up at a month or two ago, and 9 psi higher than the other tires. Any clue what happened? I'm a little confused __________________ 2008 BMW 335i (E90) - Black on Black! 2010 Audi Q7 - Gray/Black
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07-09-2013, 12:01 PM	#2
VMRWheels BimmerPost Supporting Vendor 2045 Rep 25,989 Posts Drives: BMW Join Date: Jun 2007 Location: Anaheim, CA iTrader: (4) Garage List 2013 BMW M3 [10.00] 2015 BMW M4 [0.00] 2013 BMW F30 [0.00] 2014 BMW F22 [0.00] 2013 BMW F06 [0.00]	It's fairly normal to lose some pressure over time. You aren't losing it at a super alarming rate. Now, I don't know why your pressure would go up on one corner but go down on the other three. Could be that whatever you checked your pressure with was inaccurate (before, or even now). If you think you have a slow slow leak from somewhere, the old soap and water method would show you exactly where. __________________ VMR\|Wheels \| 714.442.7916 \| sales@velocitymotoring.com \| www.velocitymotoring.com \| facebook \| flickr \| Instagram
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07-09-2013, 12:10 PM	#3
N8N Lieutenant Colonel 170 Rep 1,843 Posts Drives: 2009 E92 335i 6MT Join Date: Sep 2012 Location: Berwyn Heights, MD iTrader: (2)	Is the weather significantly warmer (as in, tens of degrees F warmer) than it was when you filled the tires? Alternately, had you been driving for a while when you checked the pressure in your tires? remember PV = nRT and what that basically means to you is that pressure scales linearly with temperature (expressed in absolute degrees, e.g. Kelvin) so a hotter tire with the same number of molecules in it as a colder tire will read more pressure. That does NOT mean that you should let air out if you check the pressures with the tires hot, just that you should check the pressure after the car has been sitting overnight for the most accurate readings/fill of your tires.
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