The folding of the trailer, also known as the "jackknifing effect", occurs when the tractor swerves and the trailer pushes from behind until it joins the tractor itself, hitting it (just as if it were a jackknife). The vehicle could then continue to move out of control and cause accidents. This article describes how the phenomenon is triggered and how to avoid it.
Steps
Method 1 of 2: Understanding the Phenomenon
Step 1. Know the causes
The book closing takes place when the tractor swerves. If the driver is unable to readily correct the trajectory, the trailer exerts pressure from behind until it begins to rotate and roll alongside the tractor itself.
Step 2. Remember that this is a different motion than swinging or skidding the trailer
The image shows the difference graphically.
Method 2 of 2: Avoid Flip Fold
Step 1. Watch out for light loads
When the trailer is carrying heavy objects, it is very unlikely that it is subject to the jackknifing effect, which usually occurs when the tow is empty or the weight is poorly distributed, factors that reduce the traction precisely where it is needed. The vehicle and trailer brakes are designed and built to operate under full load and exert excessive force when there is no material being transported. When the brakes are applied, the wheels could lock causing a skid.
Step 2. Distribute the braking force over the maximum distance possible by gradually increasing the pressure on the pedal and reducing the speed
In this regard it is important to drive respecting the safety distances with the vehicles in front of you and try to anticipate what is happening in front of you; in doing so, you have plenty of time to pull over, especially on slippery and downhill roads.
Step 3. Avoid having to brake or even decelerate when cornering
Apply the brakes when the vehicle is still on the straight and approaching the turn. Slow down a little more than necessary and release the pedal before starting to turn the steering wheel. As you go around the corner, press the accelerator a little bit to prevent the drive wheels from losing grip. If you approach slowly enough, you are able to increase your speed as you go around the corner.
Downhill curves are particularly tricky. If you are traveling on a road with a steep incline and need to turn right or left, do not assume that the trailer follows your movements. Inertia and gravity cause it to maintain a straight trajectory; you must therefore reduce your speed or even stop before turning. When you are satisfied with the control you have over the towing momentum, you can take the turn
Step 4. If you have to perform an evasion maneuver, do not brake and abruptly swerve at the same time
First, brake to reduce speed as much as possible and then release the pedal to steer, in order to maintain control of the vehicle; once you have avoided the obstacle, you can apply more pressure to the brakes if necessary.
If you have to perform an emergency stop, for example a child is running across the road in front of the truck, do not step hard on the brake pedal; instead you should press it and then operate the clutch to prevent the vehicle from continuing to move forward. Keep your hands on the wheel at 10 o'clock and 2 o'clock with your thumbs on the top edge; press the edge of the steering wheel and keep your elbows locked
Step 5. Be very careful when using the engine brake or retarder (electromagnetic, hydraulic or Voith system) on slippery roads
These systems can block the motor axis and cause book closing. The engine brake and the retarder act only on one axle, while the braking system involves all the wheels. If you are forced to prime it downhill but the road is slippery, start by gently reducing speed with the brakes and then activate the retarder; the same applies if you have to engage a low gear ratio.
Step 6. The jackknifing effect is born as a skid, the main goal is therefore to avoid wheel spin
If the vehicle still begins to lose traction, immediately take your foot off the brake pedal and correct the skid as you would with a non-articulated vehicle. If you do not intervene, the skid worsens due to the pressure exerted by the trailer towards the tractor which induces the folding.
Step 7. Perform proper maintenance on both the trailer and tractor unit
Uneven braking force, worn tires and malfunctioning suspension increase the risk of losing control.
Step 8. Modern ABS braking systems, originally developed to prevent planes from skidding on the runway, are now also fitted to heavy vehicles
They automatically sense when a tire slips and adjust the force to prevent the wheels from locking.
Warnings
-
As a general rule, the shinier the road surface, the more slippery it is; however, the conditions described below are particularly dangerous:
- A light layer of snow on the asphalt surface or, worse, an icy road covered with little snow.
- During the cold months be aware of the risk of "black ice". It is invisible ice, a thin layer that forms around the particles that are on the asphalt and that cannot be identified by simple sight.
- A downpour after a long period of drought; in this case, the water mixes with the dust on the road, forms bubbles, as if it were soapy, and is just as slippery.
- Fallen leaves on a wet road can cause skids that trigger the trailer to fold.
