In the context of fire apparatus, what is a common source of error related to tire diameters on duals?

• A. Using mismatched brand tires
• B. Using mismatched diameters beyond tolerance
• C. Using new tires too early
• D. Choosing tires with too much traction

Answer: (B)

The main idea is that dual tires on an axle must have nearly identical rolling circumferences so they rotate in sync and share the load evenly. When the two tires on the same axle have diameters that differ beyond what’s allowed, they don’t travel the same distance per revolution. The drivetrain and differential then have to compensate, which can force one tire to slip or drag, overheat tires, wear them unevenly, and create instability or binding especially during braking or turning. On a fire apparatus, where loads are heavy and reliability is critical, this mismatch can lead to handling and safety issues, so keeping tire diameters within tolerance is the common source of error to watch for.

Mismatched brand isn’t the core problem if the sizes match; new tires too early doesn’t address diameter differences; and tires with too much traction doesn’t directly relate to diameter tolerance.