Home › CDL Practice Tests › Combination Vehicles Questions › Question 137
Which condition most often sets up a trailer jackknife?
- A.The trailer being loaded with the heaviest items at the front
- B.Driving below 25 mph on dry pavement
- C.Using the parking brake to hold the vehicle on a grade
- D.Trailer wheels locking on a slick or lightly loaded axle while the tractor keeps rolling forward
Correct answer
D. Trailer wheels locking on a slick or lightly loaded axle while the tractor keeps rolling forward
Why
The trailer swings because its locked wheels lose side grip while the moving tractor keeps pushing at the kingpin. Slick surfaces, hard braking, and light trailer loads all make that lockup more likely.
Manual topic: Combination Vehicles - Skids and Jackknifing · From the Combination Vehicles practice bank (CV-137).