<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">Heat. Your increased load causes heat. You want higher pressures for increased sidewall strength, btw. The math is simple - <div><br></div><div> PV=nRT. V is constant, so as T increases, P increases. Or, simplified, the density of air is <div><br></div><div>2.7*P/T. As t increases, the air expands in a given volume and pressure increases. </div><div><br><div id="AppleMailSignature">Ron Soave</div><div><br>On Aug 28, 2018, at 10:20 AM, Mike Rambour via Spridgets <<a href="mailto:spridgets@autox.team.net">spridgets@autox.team.net</a>> wrote:<br><br></div><blockquote type="cite"><div>
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I have to partially agree. I also have never seen the 32 degree
specification and that would seem near impossible for any owner or
even tire shop to check the pressure at that point (maybe a few
lucky ones in the cold part of the country for a few months).<br>
<br>
But Tire pressure is not the same when hot or cold, check your
tire pressure in the morning before driving and then check it
again after 10-15 miles down the freeway and you will see it has
increased. In my new truck, I have tire pressure monitors, I will
start at 35psi in the morning and average 39psi on the freeway.
Its interesting to see that the front tires will get to 40psi and
rears stay at 39psi, but when towing a heavy trailer, the rears
will get to 41-42psi while the fronts stay at 39. And this is
always starting at 35 cold, by cold I mean mid-60's ambient
temperature and before driving at all. I assume the difference in
PSI is due to weight on the tire at the time, motor up front and
1-2psi then empty rear of truck, towing its the other way around,
more weight on the rear. And no, I do not use my TPM to set my
tire pressure, I use a proper tire gauge, but the TPM is never
more than 1 psi off.<br>
<br>
Some people add PSI in the belief that they will get better
mileage, doubt its true after a certain point. Yes, if your tires
are under pressured, then getting it to manufacturers specs will
improve mileage (by what, a few tenths maybe, assuming the tires
are not flat to begin with) but after you are in spec, I seriously
doubt it will improve the mileage more than a tenth of a MPG.<br>
<br>
Mike<br>
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<br>
On 8/28/2018 5:39 AM, Rick Fisk via Spridgets wrote:<br>
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<div>Allen,</div>
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<div id="AppleMailSignature">Not wanting to start anything here,
but your tire pressure recommendations don't make sense to me.
I've never seen the recommended tire pressure is at 32 degrees
F spec in a manual anywhere. ??? Seems to me the tire pressure
should be the same no matter what the temperature is.</div>
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<div id="AppleMailSignature">For every 10 degree F rise in air
temperature the pressure in your tires will rise about 1 psi and
fall 1 psi for every 10 degree drop in temperature. So to
maintain the car manufacturer's recommended tire pressure you
should reduce the pressure when the temp goes up and raise it
when the temp drops.</div>
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<div id="AppleMailSignature">Why would you always add 5 psi to the
recommended pressure? Seems to me the car manufacturer probably
knows best when it comes to recommended tire pressures for their
cars. </div>
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<div id="AppleMailSignature">Rick</div>
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Sent from my keyboard</div>
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On Aug 27, 2018, at 10:39 AM, Allen Hefner via Spridgets <<a href="mailto:spridgets@autox.team.net" moz-do-not-send="true">spridgets@autox.team.net</a>>
wrote:<br>
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<div dir="ltr">Don't forget that the recommended tire pressure
in the manuals is at 32 degrees. You usually add 1 PSI for
every 10 degrees above freezing. Nobody seems to know that
anymore. The manuals just say ## PSI cold. I always just add
5 PSI to the recommended pressure.
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<div>Allen Hefner</div>
<div>Norristown, PA</div>
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<pre class="moz-signature" cols="72">--
A gun is like a parachute, if you need one but don't have it,
you'll probably never need one again.</pre>
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