SGI SGI Heavy Commercial Vehicle Operations 2 — Questions and Answers
Question 1: What is 'jackknifing' in a tractor-trailer combination?
- The trailer swings out at an angle relative to the tractor during braking (Correct answer)
- The tractor tips over independently
- Both units spin simultaneously
- The fifth wheel detaches under heavy braking
Correct answer: The trailer swings out at an angle relative to the tractor during braking
Jackknifing occurs when excessive braking causes the trailer to swing outward, folding the combination like a closing jackknife.
Question 2: What is the correct way to back a tractor-trailer to the left?
- Turn the steering wheel to the right to move the trailer to the left (Correct answer)
- Turn the steering wheel to the left to push the trailer right
- Use only mirrors without steering input
- Accelerate and use the trailer brake
Correct answer: Turn the steering wheel to the right to move the trailer to the left
To back a trailer to the left, the driver turns the steering wheel to the right, which pushes the rear of the trailer to the left.
Question 3: What is the 'off-tracking' phenomenon in large vehicles?
- Rear wheels follow a shorter path than front wheels around curves (Correct answer)
- Rear wheels skid on curves
- The trailer disconnects during sharp turns
- Front wheels lose traction on corners
Correct answer: Rear wheels follow a shorter path than front wheels around curves
Off-tracking means the rear axles of a large vehicle track inside the path of the front wheels, requiring drivers to swing wider on turns to avoid hitting curbs.
Question 4: What is the minimum depth allowed for tire tread on a commercial vehicle's front steering axle?
- 4.8 mm (6/32 inch) (Correct answer)
- 1.6 mm (2/32 inch)
- 3.2 mm (4/32 inch)
- 6.4 mm (8/32 inch)
Correct answer: 4.8 mm (6/32 inch)
Front steering axle tires require a minimum of 4.8 mm (6/32 inch) of tread depth due to their critical role in vehicle control.
Question 5: What should a commercial driver do when a tire blows out on a rear axle?
- Hold the wheel firmly, gradually ease off the throttle, and steer straight to a safe stop (Correct answer)
- Brake hard and steer to the shoulder immediately
- Accelerate to maintain stability
- Apply the trailer brake immediately
Correct answer: Hold the wheel firmly, gradually ease off the throttle, and steer straight to a safe stop
Holding the wheel firmly and gradually slowing down maintains control, as sudden braking can cause the vehicle to swerve or jackknife.
Question 6: What does 'gross vehicle weight rating' (GVWR) mean?
- The maximum operating weight of a fully loaded vehicle as specified by the manufacturer (Correct answer)
- The weight of the vehicle without cargo
- The maximum cargo weight only
- The combined weight of all axles
Correct answer: The maximum operating weight of a fully loaded vehicle as specified by the manufacturer
GVWR is the maximum total weight of the vehicle including the vehicle itself, fuel, passengers, and cargo, as specified by the manufacturer.
SGI SGI Heavy Commercial Vehicle Operations 2
What is 'jackknifing' in a tractor-trailer combination?