Safety Systems,Maintenance,Misc

Checking your tire pressure? Temperature matters, too, so remember: Measuring psi when things are cool is the rule.

During regular use – even on comfortable, cold, or cloudy days – a truck tire heats up when it’s rolling. This heat dissipates at a rate that depends on factors like the weather and the ambient temperature. “Thermal equilibrium” defines the point at which the rate the tire is generating heat is equal to the rate at which the heat is dissipating.

Hotter weather – or even a significant amount of time sitting in direct sunlight – has an impact on heat buildup in a tire, as well as the rate at which that heat dissipates. Other factors affecting tire heat include repeated hard braking, high-speed turns, weight overload, and mechanical issues such as out-of-balance or dragging brakes. Any of these can push a tire past its thermal equilibrium, gaining heat more rapidly than it can be shed.

Most experts consider 195 degrees Fahrenheit as the “line in the sand” when it comes to tire temperature: Beyond that point, the temperature will start impacting tire life. At 250 degrees, a tire will start to lose structural strength, could begin experiencing tread reversion and the tire will begin to lose strength.

Avoiding weakening or damaging your tires is reason enough to use a Tire Pressure Monitoring System (TPMS) that includes temperature sensors and high temp alerts – but there’s also the pressure side of things. As a tire heats up, its pressure increases. A typical tire inflated to 100 psi, undergoing normal use at 68 degrees Fahrenheit, tends to build up enough heat to increase 10 to 15 psi as it reaches thermal equilibrium. A general rule of thumb is that for every 10 degree increase in tire temperature, the tire’s pressure will increase by 2 psi.

That heat-induced pressure increase, though, can make things tricky: The problem is that if you adjust a warm tire by lowering its pressure, it’s likely that when the tire cools, you’ll be running on a low-pressure tire instead. Not a good trade-off. (Bendix really doesn’t recommend ever letting air out of a hot tire for this very reason.)

Bendix’s SmarTire® TPMS takes some of the uncertainty out of the temperature/pressure puzzle by incorporating temperature compensation into its driver displays and alerts. What it does is provide a deviation value that shows the amount of overinflation or underinflation from the tire’s cold inflation pressure (CIP), automatically taking into account any pressure increase due to temperature. This helps address changing situations such as whether a tractor or trailer has been parked for an extended period of time, or whether it’s just come to a rest after hundreds of miles.

There’s no TPMS system that can warn of or prevent an instantaneous tire blowout due to a road hazard or similar situation, however. And fleets and drivers should follow all equipment and tire manufacturer guidelines for tire fitment, replacement, inspection, and repair.

If you want to learn a bit more, there’s a Bendix Tech Talk video on TPMS at our YouTube channel . Stay cool!

Bendix Blog

Technical and industry insight from OUR experts.

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