BENDIX SmarTire Operator's Manual page 12

S T ™ TPMS T C
MAR IRE EMPERATURE OMPENSATION
Since a tire's contained air pressure naturally increases as a vehicle moves,
it can be difficult to tell if a hot tire is under-inflated. Without some form of
temperature compensation, a hot tire that is under- inflated might appear to
be fine because it's contained air pressure is at or above its cold inflation
pressure (CIP).
When checked using a handheld gauge or a tire monitoring system that does
not measure operating temperature, an under-inflated tire can appear to be
normal. When equipped with SmarTire TPMS tire sensors mounted
™
inside the tire measure both tire pressure and temperature in order to
provide "Temperature Compensated" pressure deviation values and
alerts. The Deviation Value represents the amount of over or under
inflation based on the tire's current temperature. This value can be used to
warn the driver of an under-inflated tire even if that tire's actual contained air
pressure is at or above its CIP. This value is also useful when maintaining
the tire as it respresents how much air should be added or removed from the
tire to bring it to the desired pressure, which the system calculates based on
the programmed CIP value and the tire's current temperature.
The advantages of temperature compensation are even more dramatic when
a tire has a slow leak. Since the leak is slow, the tire may appear over an
extended period of time to be properly inflated when it is actually dangerously
under-inflated and operating well above its temperature capacity. Eventually,
the tire will become so hot that its structure will degrade and then fail in the
form of a blow-out and / or tire fire.
To further illustrate this concept, on the SmarTire display you may see that
the pressure is above the CIP, but due to the temperature of the tire, the
pressure is actually low or high depending on the Deviation value. The image
below shows a tire with a CIP value of 110 PSI at ambient temperature. This
is a properly aired tire and therefore the deviation value displayed is zero.
65
1
°F
Tire Air Temperature
Pressure Deviation
110
0
(Temperature
Tire Air Pressure
psi
Compensated)
psi
As the vehicle is driven and the tires warm up, the
85
1
°F
pressure measured will change due to this natural
115
0
increase in the temperature. The Pressure Deviation
psi
psi
value compensates for this change in temperature
and displays a zero value for a properly air tired.
BW8002 Page 12