Whats your Tire Pressure?



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Thread: Whats your Tire Pressure?

  1. #21
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    Quote Originally Posted by jgiurleo View Post
    Could it be? One would usually check/fill tires when they're cold. So the tires inflated with cold air in the winter... which expands in the heat of the summer. So even if some air leaked out, you're still up from where you were in the winter.

    I'm not sure how much more pressure the air would exert on the tire with, say, a 60 degree temperature increase for the summer months, (PV=nRT... maybe later!) but I've un-scientifically experienced the same thing with my cars.
    I just did a couple of quick calculations and came up with a very rough estimate that suggests that if you have 36 psi in a tire at 20 degrees, and then warm the tire up to 80 degrees, said tire will register 42 psi, and that works out to roughly 1 psi for every ten degrees. Given that I can only roughly estimate the volume of air in the tires, the above calculations are very iffy.

    That said, given that I put 38 in the tires on a day that I think was at least 20 degrees (maybe a bit lower), and given that I took the pressure readings Saturday morning at something over 70 degrees, that would equate to a 5 pound increase in pressure, and I showed an extra 4 on the gauge.

    That of course brings me back to my original question, could it be possible that all four of my new tires lost virtually no air in eight months of driving?
    Sold: 1998 DGC Sport 3.8 (Final odo: 178,000 miles)
    Sold: 1998 Chrysler T&C LXi 3.8 (Final odo: 190,000 miles)
    Sold: 2003 DGC ES 3.8 (Final odo: 172,000 miles)
    1998 Audi A4 Quattro (5-Speed manual)
    2001 Honda Accord EX V6 (4-Speed automatic)
    2009 Mazda3 i Touring (5-Speed manual)
    2012 VW GTI (6-Speed manual)

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  3. #22
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    Quote Originally Posted by jgiurleo View Post
    Could it be? One would usually check/fill tires when they're cold. So the tires inflated with cold air in the winter... which expands in the heat of the summer. So even if some air leaked out, you're still up from where you were in the winter.

    I'm not sure how much more pressure the air would exert on the tire with, say, a 60 degree temperature increase for the summer months, (PV=nRT... maybe later!) but I've un-scientifically experienced the same thing with my cars.

    You have hit on an important point. All tire pressure readings aren't necessarily equal. From the following article:
    http://www.tirerack.com/tires/tirete....jsp?techid=73

    And finally, if the vehicle is parked in the sun, the sun's radiant heat will artificially and temporarily increase tire pressures.

    We put some of these theories to the test at the Tire Rack. First, we mounted two tires on wheels. We let them sit overnight to equalize and stabilize their temperatures and pressures. The following morning we set them both to 35 psi. One tire and wheel was placed in the shade while the other was placed directly in the sun. We then monitored the ambient temperatures, tire temperatures and tire pressures through the day. As the day's temperatures went from 67 to 85 Fahrenheit, the tire that was kept in the shade went from our starting pressure of 35 psi to a high of 36.5 psi. The tire that was placed in the sun and subject to the increase in ambient temperature plus the sun's radiant heat went from our starting pressure of 35 psi to a high of 40 psi. In both cases, if we had set our tire pressures in the afternoon under the conditions of our evaluation, they would have been between 2 and 5 psi low the following morning.

    Next we evaluated the affects of heat generated by the tire's flexing during use. We tried to eliminate the variable conditions we might encounter on the road by conducting this test using our "competition tire heat cycling service" that rolls the tires under load against the machine's rollers to simulate real world driving. We monitored the changes in tire pressure in 5-minute intervals. The test tires were inflated to 15 psi, 20 psi, 25 psi and 30 psi. Running them all under the same load, the air pressure in all of the tires went up about 1 psi during every 5 minutes of use for the first 20 minutes of operation. Then the air pressures stabilized, typically gaining no more than 1 psi of additional pressure during the next 20 minutes. This means that even a short drive to inflate your tires will result in tires that will probably be under-inflated by a few psi the following morning.

    Add all of these together, and you can understand why the conditions in which you set your vehicle's tire pressures are almost as important as the fact that you do set it.
    2007 GC SXT - Magnesium - S&G - 3.8L - 115,600 kms
    2002 GC Sport - Stone White - 3.3L - 314,240 kms
    2003 Jeep TJ Sport - 4.0L - 246,430 kms

  4. #23
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    Quote Originally Posted by shipo View Post
    That of course brings me back to my original question, could it be possible that all four of my new tires lost virtually no air in eight months of driving?
    Maybe you filled the tires and don't remember it. Like those people who wake up with candy bar wrappers on the floor next to their beds. You never know.
    2009 Dodge Grand Caravan SXT (3.8L), Light Sandstone Metallic, 125K miles
    2005 Volvo XC70, 160K miles

    Previous van: 2002 Chrysler T&C, eX (3.8L)

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    Goodyear Assurance Comfort Tread - 36 psi all around.
    2011 Chrysler T&C Limited 3.6L V6
    2004 Honda CRV LX 2.4L I4
    2000 Honda Civic VP 1.6L I4

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    Now here is another wrench into the gears.

    What about using Nitrogen in the tires? Benefit or BS?
    '08 Town and Country LTD 4.0L
    Built Sept. 2007, took delivery Dec. 2007
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  7. #26
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    I've never run nitrogen in any of my tires... but it can't possibly make that much of a difference.
    2009 Dodge Grand Caravan SXT (3.8L), Light Sandstone Metallic, 125K miles
    2005 Volvo XC70, 160K miles

    Previous van: 2002 Chrysler T&C, eX (3.8L)

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    Quote Originally Posted by Gumby View Post
    Now here is another wrench into the gears.

    What about using Nitrogen in the tires? Benefit or BS?
    I have used nitrogen. It's overated. I am not using it now.
    2007 GC SXT - Magnesium - S&G - 3.8L - 115,600 kms
    2002 GC Sport - Stone White - 3.3L - 314,240 kms
    2003 Jeep TJ Sport - 4.0L - 246,430 kms

  9. #28
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    Quote Originally Posted by Gumby View Post
    Now here is another wrench into the gears.

    What about using Nitrogen in the tires? Benefit or BS?
    Given: At best if you fill your tires with pure nitrogen you're going to be lucky to get the purity inside the tire much above 90% pure. Why? Because unless you mount the tire to the rim in a room that is 100% nitrogen, then you're going to start out with a tire full of "air".

    Given: Air is a touch over 78% nitrogen.

    I have seen science that shows that pure oxygen (O2) can pass through a layer of pure rubber four times faster than pure nitrogen (N2), however, the "rubber" that we find in modern tires isn't pure. Based upon all of my readings, the polymer chains of the recent vintage of tires are simply too tight to allow O2 to permeate through the walls of the tires. Are there some tires on the market that bleed more "air" than they would nitrogen? Probably.

    Assume "probably" correct. Then the next question is "is there really a difference between air and nitrogen?" Personally I'm thinking not. Why? Simply because given seasonal temperature fluctuations, tire pressures are going to get adjusted by the maintainer of the vehicle far too often to make any difference.

    Back to the Cooper CS4 Touring tires. Hmmm, I wonder if Cooper's new manufacturing process somehow forms rubber that has even tighter polymer chains than is found in the typical tire.
    Sold: 1998 DGC Sport 3.8 (Final odo: 178,000 miles)
    Sold: 1998 Chrysler T&C LXi 3.8 (Final odo: 190,000 miles)
    Sold: 2003 DGC ES 3.8 (Final odo: 172,000 miles)
    1998 Audi A4 Quattro (5-Speed manual)
    2001 Honda Accord EX V6 (4-Speed automatic)
    2009 Mazda3 i Touring (5-Speed manual)
    2012 VW GTI (6-Speed manual)

  10. #29
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    Quote Originally Posted by shipo View Post
    Given: At best if you fill your tires with pure nitrogen you're going to be lucky to get the purity inside the tire much above 90% pure. Why? Because unless you mount the tire to the rim in a room that is 100% nitrogen, then you're going to start out with a tire full of "air".

    Given: Air is a touch over 78% nitrogen.

    I have seen science that shows that pure oxygen (O2) can pass through a layer of pure rubber four times faster than pure nitrogen (N2), however, the "rubber" that we find in modern tires isn't pure. Based upon all of my readings, the polymer chains of the recent vintage of tires are simply too tight to allow O2 to permeate through the walls of the tires. Are there some tires on the market that bleed more "air" than they would nitrogen? Probably.

    Assume "probably" correct. Then the next question is "is there really a difference between air and nitrogen?" Personally I'm thinking not. Why? Simply because given seasonal temperature fluctuations, tire pressures are going to get adjusted by the maintainer of the vehicle far too often to make any difference.

    Back to the Cooper CS4 Touring tires. Hmmm, I wonder if Cooper's new manufacturing process somehow forms rubber that has even tighter polymer chains than is found in the typical tire.
    I have seen tires retain pressure over long periods of time, especially Winter wheels in storage over the Summer or Summer wheels in storage over the Winter. I believe it depends mostly on the rim seal being 100%. Then there's the temperatures of the respective checks to take in account as well.
    2007 GC SXT - Magnesium - S&G - 3.8L - 115,600 kms
    2002 GC Sport - Stone White - 3.3L - 314,240 kms
    2003 Jeep TJ Sport - 4.0L - 246,430 kms

  11. #30
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    36 psi all around per the label on the door of T&C
    Michelin Destiny 215/65R-16.
    2002 Town and Country LXI - 3.3L - 133,000 miles
    1988 Dodge Grand Caravan LE - 3.0L - 270,000 miles (Gone but never forgotten)

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