Bendix Commercial Vehicle Systems SMARTIRE TPMS OPERATORS MANUAL - Manual (Page 12)

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The charts above are to be used as a guide only. Always refer to the tire / vehicle
manufacturer’s recommendations for minimum cold inflation pressures.
Thermal Equilibrium
As a vehicle moves, its tires naturally heat up due to friction from the road and the flexing of its
side-walls. Weight, vehicle speed and a tire’s starting inflation pressure all have an impact on how
much and how quickly heat is generated.
As the tire generates heat, its pressure increases, causing a reduction in side-wall flexing. Less
side-wall flexing and road resistance combined with air rushing past the tire as the vehicle moves
effectively counteracts the conditions that cause the tire to heat up. As a result, the temperature
increase tapers off until the tire reaches a point of balance called Thermal Equilibrium.
Tire “Thermal Equilibrium” is the point where the heat being generated is equal to the heat being
dissipated. Tires are designed with the principles of temperature and pressure in mind in order for
them to achieve Thermal Equilibrium. Once a properly inflated tire reaches Thermal Equilibrium, it
will operate at its peak; providing the best performance, handling, tire life and fuel economy.
SmarTire
™
TPMS Temperature Compensation
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 its contained air pressure is at or above its cold
inflation pressure (CIP).
For example, a tire correctly inflated to a CIP of 105 PSI at 65°F will reach thermal equilibrium
when its temperature increases to 152°F and its pressure increases to 125 PSI. A tire starting at
95 PSI at 65°F (10 PSI under inflated) would have to reach 202°F for it to reach thermal