A driver checks a tire during a stop in extreme heat and finds the measured air pressure is higher than the vehicle's specified cold inflation pressure. What does 49 CFR 393.75(i) say the driver should do?

Explanation

A driver should account for heat buildup rather than let air out of a hot tire. Under 49 CFR 393.75(i), a vehicle may not be operated on a tire below its specified cold inflation pressure, but if the tire has heated up from recent driving, the regulation directs the driver to estimate the true cold inflation pressure by subtracting the heat buildup correction listed in the section's table from the measured reading, since a hot tire reads higher than its actual cold pressure. Letting air out to force the gauge down to the cold-pressure figure leaves the tire dangerously underinflated once it cools, which is exactly the failure this rule is designed to prevent. The wrong options fail for a shared reason: two invent a response the regulation does not require (releasing air to match the number, or discarding the reading as unregulated) and one invents a pass/fail rule the section does not state, since a pressure reading above the cold figure on a hot tire is expected, not evidence of failure.

Source: 49 CFR 393.75(i)