Quote:
Originally Posted by CapriRacer
Allow me to start in a different place:
What to ignore:
Elevation: Even at 5,000 feet (Denver), the amount of inflation pressure change
from sea level is only 2 1/2 psi - not enough to worry about.
Humidity: Just not a factor
So we are only talking about temperature vs pressure.
In summer, we can expect at 20°F change from early morning to the hottest
point of the day. That would be a 4% change - 80 psi to 83 psi - again, not
enough to worry about.
The problem in winter is 2 fold:
1) Water vapor can freeze about of humid air at as little as 37°F. That means
that one should avoid check inflation pressures when it gets below - say - 40°F.
That also means that, in winter, one should anticipate colder temperatures and
set the tire inflation pressures to cover the worst temperatures in the coming
months. When I lived in Michigan, the worst temperature I anticipated was
-20°F, but I would set the pressures for 0°F, reasoning that if it got to -20°F, I
was not going to travel fast (which causes additional stresses) nor for very long.
Which brings me to:
2) Setting the pressure in a warn environment, with the expectation of
operating in a cold environment.
So lets say the pressures are set at 50°F, and the expect operating temperature
is 0°F, then the expect loss of pressure would be 10%. So an 80 psi tire should
be set at 88 psi.
Doesn't that exceed the max pressure on the sidewall? Yes, but not only are
tires designed for a much higher pressure (long story why that is!), but the tire
isn't expected to operate at that pressure - the tire will cool down to a lower
pressure.
You can use that chart to help set pressure for anticipated conditions -
except that the chart doesn't show what I just outlined above. Ergo,
I would recommend NOT using this chart.
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Neither does a customer I showed it to where I work.
He said if my car specified 32psi cold tire pressures, setting them to the 37psi the grid suggests, even during below freezing dawn temperatures, would, in his own words, "... f - k up the tires! ..."
I told him you got most idiots these days running anywhere from 40psi up to what's stamped on their tire sidewalls, and you might be risking your life to suggest they do otherwise!
I do maintain 34psi though, from December through March, and 33psi the rest of the year - primarily to account for possible tire gauge discrepancy. This Accord, even with the 50-series low profile rubber OEM at its trim level, seems to do everything and handle most predictably and securely, at those pressures, even on the rare occasion I push things, IE: take a corner a little faster than I usually do, etc.
So I think Honda does its homework when it comes to what's on their door frame decals.