Bendix Commercial Vehicle Systems SmarTire Trailer-Link Op Manual - Manual (Page 9)

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1.4 Fundamentally, Why Is Temperature
Monitoring Important?
The Pressure/Temperature Relationship
Tire manufacturers specify that tire pressures should be checked and adjusted
when a tire is “cold”, but most people may not know why, or even what a
“cold tire” is. The temperature of a tire actually has a significant impact on
its inflation pressure.
According to tire manufacturers, a tire is considered to be “cold” when
its temperature is 65°F (18°C). The inflation values provided by vehicle
manufacturers, fleet maintenance personnel, or industry-published load
inflation tables are called ‘Cold Inflation Pressures’ (CIP) because they
represent the correct amount of pressure a tire should be inflated to when
it is “cold”. The reason that tires have cold inflation pressures set at
specific temperatures is because a tire’s pressure will change relative to its
temperature.
Air naturally expands when heated and contracts when cooled. Inside a
contained vessel such as a tire, this expansion and contraction causes a
change in contained air pressure. As a tire heats up, its pressure will naturally
increase and as it cools down, its pressure will naturally decrease.
For example, a tire inflated to a CIP of 105 PSI at 65°F will increase in pressure
to 125 PSI at 152°F and decrease in pressure to 97 PSI at 32°F. The SmarTire
Trailer-Link ™ tire monitoring system considers these changes in temperature
and pressure as part of normal operation and adapts accordingly to provide
more accurate information while helping to prevent false alerts.
Tire manufacturers never recommend inflating a tire to less than the specified
cold inflation pressure. In extreme cases, the beads of a commercial tire
can unseat if its pressure gets too low resulting in a catastrophic tire failure.
Always refer to the vehicle manufacturer’s recommendations for minimum
cold inflation pressures.