air pressure measurement adjustment based on outside temperature

bmw_guy_2020 · 02-01-2011, 01:14 PM

Do you adjust your air pressure measurement based on outside temperature?

I remember hearing that if you've been driving around all day then the air pressure measurement for your tires will be skewed.

So what if the outside temperature is freezing? Like 20F?

I measured the air pressure in my front tires this morning and they were at 20psi but I'm not sure if this low measurement was partially due to the freezing outside temps.

So would you expect this air pressure measurement to be higher if the outside temp were 80F+?

Tim B. · 02-01-2011, 01:27 PM

All your tires were at 20psi?? Is the car garaged? Obviously pressure increases as temp increases and same with cold(decreases) but it's usually not more than a few lbs.

**ben@tirerack** · 02-01-2011, 01:38 PM

Not exact, but a good rule of thumb: every 10 degrees will roughly equal 1psi. So if your tires are at 20psi at 20 degrees, they'd be at ~26psi at 80.

For street cars (circuit racing is a whole different subject), air pressure is properly measured when the tires are 'cold', meaning at whatever the current ambient temperature is. This will often mean adding air when the weather turns cold, and sometimes bleeding air out if you move rapidly from a cold to a hotter climate.

bmw_guy_2020 · 02-01-2011, 01:50 PM

Quote:

Originally Posted by ben@tirerack

Not exact, but a good rule of thumb: every 10 degrees will roughly equal 1psi. So if your tires are at 20psi at 20 degrees, they'd be at ~26psi at 80.

For street cars (circuit racing is a whole different subject), air pressure is properly measured when the tires are 'cold', meaning at whatever the current ambient temperature is. This will often mean adding air when the weather turns cold, and sometimes bleeding air out if you move rapidly from a cold to a hotter climate.

Ben - thanks for that math! I like reasoning supported by math!

02-01-2011, 01:14 PM	#1
bmw_guy_2020 Private First Class 30 Rep 182 Posts Drives: Mercedes CLS 550 Join Date: Sep 2010 Location: Dallas, TX iTrader: (0)	air pressure measurement adjustment based on outside temperature Do you adjust your air pressure measurement based on outside temperature? I remember hearing that if you've been driving around all day then the air pressure measurement for your tires will be skewed. So what if the outside temperature is freezing? Like 20F? I measured the air pressure in my front tires this morning and they were at 20psi but I'm not sure if this low measurement was partially due to the freezing outside temps. So would you expect this air pressure measurement to be higher if the outside temp were 80F+?
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02-01-2011, 01:27 PM	#2
Tim B. Lieutenant 19 Rep 561 Posts Drives: 2010 Jet Black E92 M3 Join Date: Dec 2009 Location: Baton Rouge, LA iTrader: (0)	All your tires were at 20psi?? Is the car garaged? Obviously pressure increases as temp increases and same with cold(decreases) but it's usually not more than a few lbs.
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02-01-2011, 01:38 PM	#3
ben@tirerack M3Post Supporting Vendor 87 Rep 964 Posts Drives: 740i Join Date: Mar 2008 Location: South Bend, IN iTrader: (0)	Not exact, but a good rule of thumb: every 10 degrees will roughly equal 1psi. So if your tires are at 20psi at 20 degrees, they'd be at ~26psi at 80. For street cars (circuit racing is a whole different subject), air pressure is properly measured when the tires are 'cold', meaning at whatever the current ambient temperature is. This will often mean adding air when the weather turns cold, and sometimes bleeding air out if you move rapidly from a cold to a hotter climate. __________________ _______________________________________________ I have accepted a new position at Tire Rack and am no longer in the sales department. gary@tirerack.com is available to assist with M3 questions.
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