Some clarification from a tire engineer.
First off, I am not going to address what the correct Cold Inflation Pressure
("CIP") is for your RV. We will assume you have read my other posts on how to learn that
number. If you haven't, simply look at the list of labels on the left side of this blog and you can review them.
There are different guidelines for Trailers vs. Motorhomes. I
want to focus only on setting the CIP
Some people want to refer to a Temperature compensation chart.
Tire Rack was off a bit till they updated their tech page last year after my input. Also Wikipedia
definition for Cold Inflation Pressure was also almost correct till I added a clarification aimed at RV owners.
The 1 Psi for 10 F is OK if your base inflation is near 40 psi but many
RVs use 80 to 110 psi.
The correct "Rule of Thumb" to use is 2% for each 10F.
pressure is not based on any laboratory standard temperature (some
claim 70 F) but is based on the tire not being warmed from either use,
i.e. being driven in previous two hours, or from being in the Sun for
previous two hours. Even partial sun can affect the reading.
"Temperature in the Shade" is the "Ambient" tire engineers are talking
about. Not temperature in a theoretical laboratory.
a situation of setting the pressure when the tires and air
is 50 F. That would be fine and we would expect the pressure to increase
by about 8% if the Ambient increased to 90 F even without driving or Sun
It is correct to say, "The ONLY time to check CIP is FIRST thing in the morning BEFORE the day's
temp has had a chance to increase and BEFORE the sun has had a chance
to shine on the tires and BEFORE you have used the vehicle."
if you are driving from the campground on top of Pike's Peak and stop
for lunch for two hours in the shade in Flagstaff where it is 90 and
check your air, you might find a change of a few psi. You could adjust
your pressure before continuing to Phoenix, where it is 120 F, but I don't
bother to adjust inflation by the 1 to 3 psi variation I observe day to
day. In my mind that is too much work.
NOTE: My personal CIP is 75/80 F/R on my
Class-C MH. Both of these pressures are more than 10% above the minimum
pressure needed to support the measured load on each tire so I have a
I usually wait till I am home and am getting ready for the next
trip before I adjust my inflation to my personal CIP, so I simply monitor
the running inflation pressure which goes up and down as ambient temperature,
driving and Sun exposure changes the inflation. My TPMS will warn me of
air loss, so all is good as I motor down the highway.
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