The tire limit speed is specified in which speed reference?

• A. Knots Ground Speed
• B. Knots Indicated Airspeed
• C. Mach
• D. Feet per Second

Answer: (A)

Tire speed limits are expressed in knots indicated airspeed because the tire’s safe operating condition depends on how fast the tire is spinning relative to the air the airplane encounters, which is best represented by indicated airspeed. As you accelerate on the runway, the wheel RPM—and thus the tire’s rotational speed—increase with the indicated airspeed. Using indicated airspeed provides a consistent limit across different altitudes and atmospheric conditions, since IAS accounts for air density changes that affect tire behavior. If the limit were stated in ground speed, the allowable tire speed would vary with headwinds or tailwinds and would not reflect the actual tire rotation or heat a tire experiences. Mach or feet per second don’t align with the tire’s design limits for typical approach-to-takeoff speeds, so they’re not used for specifying tire limits.