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Difficulty: Very hardTire Failure and Blowouts

During a pre-trip inspection of a fully loaded five-axle tractor-trailer, you measure the tread depth on the right-side dual tires of the forward drive axle. The inner tire measures 4/32-inch and the outer tire measures 2/32-inch. Two hours later, while descending a 6% grade at highway speeds, you hear a loud bang followed immediately by a violent fishtailing motion of the tractor and trailer, though the steering wheel remains completely stable in your hands.

Based on these symptoms and the pre-trip findings, which of the following correctly identifies the nature of the failure, the regulatory status of the inspected tires, and the legally mandated immediate physical response?

  1. A
    The vehicle has experienced a front steer-tire blowout because a 2/32-inch tread depth is illegal on a commercial vehicle; you must firmly grip the steering wheel and apply steady service brake pressure to counteract the downgrade acceleration.
  2. B
    The vehicle has suffered a drive-tire failure caused by the legally compliant but mismatched duals; because this occurred on a downgrade, you must immediately employ the snub braking technique to prevent a runaway vehicle scenario while managing the sway.
  3. The vehicle has suffered a rear drive-axle tire failure, potentially influenced by unequal load sharing from the mismatched but legally compliant dual tire treads; you must grip the steering wheel firmly, completely avoid all braking, and allow the vehicle to decelerate organically before safely pulling off the road.Answer
  4. D
    The vehicle has suffered a rear dual tire blowout due to operating with a prohibited 2/32-inch tread depth on a drive axle; you should actuate the trailer hand valve to create drag, stretching the combination out to mitigate the severe fishtailing motion.

Answer

The correct response identifies a rear drive-axle blowout involving legally compliant tires, and mandates holding the steering wheel firmly without applying any brakes until the vehicle slows down.
The correct choice accurately synthesizes all three regulatory and operational components: 1) It correctly identifies that fishtailing without a steering pull means a rear tire has blown; 2) It acknowledges that 2/32-inch is the legal minimum for drive tires; and 3) It adheres to the strict, universally mandated rule to never brake during an active blowout, regardless of the terrain.

Step-by-Step Solution

1
Analyze the tire tread depths from the pre-trip inspection.
The 2/32-inch and 4/32-inch depths on the drive axle are identified as legally compliant.
Federal regulations require a minimum of 4/32-inch on steer tires, but only 2/32-inch on all other tires, including drive tires.
2
Diagnose the location of the blowout based on the physical symptoms.
The failure is isolated to the rear (drive or trailer) tires.
A loud bang followed by fishtailing, with no active pulling on the steering wheel, is the classic presentation of a rear tire blowout. A front steer blowout would cause a heavy pull on the steering wheel.
3
Determine the correct immediate physical response to the blowout.
The driver must stay off the brakes entirely and hold the steering wheel firmly.
Applying the brakes (service, trolley, or snub braking) during an active blowout causes a massive transfer of forces to the remaining tires, frequently resulting in a total loss of control or rollover. This rule applies even on steep downgrades.

Key Concept

Tire Failure Identification and Emergency Response Protocol
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Topics

Tire Failure and Blowouts

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