Please ensure Javascript is enabled for purposes of website accessibility Skip to main content

Truck AccidentThe Jackknife Jeopardy: Understanding the Physics Behind This Deadly Truck Maneuver

May 7, 20240

A jackknife is one of the most dangerous maneuvers that can occur when driving a tractor-trailer or other large truck. It happens when the trailer swings out and folds against the cab of the truck, forming a V or L shape. This causes the entire rig to pivot around the point where the folding occurs. Jackknifing is extremely hazardous because it can result in complete loss of control of the vehicle. Understanding some basic physics can help explain why jackknifing happens and how to prevent it.

What Causes a Jackknife?

There are two main forces that lead to a jackknife – the force between the tires and the road surface, and inertia. Friction between the tires and road provides the force that makes a vehicle accelerate, brake, and turn. This force is not always consistent, however. If the tires lose traction, friction is reduced and the driver can lose control.

Inertia is the tendency of an object in motion to stay in motion. A jackknife occurs when the trailer has more inertia than the truck, so it pushes forward on the truck when braking. This lifts the truck’s front wheels off the road, eliminating tire friction and steering control. The trailer then swings around into its “jackknife” position.

Braking and Jackknifing

Hard braking is one of the most common causes of a jackknife. When brakes are applied quickly, they create a large stopping force on the tires. If this force exceeds the available friction between the tires and road, a skid can occur. The truck’s wheels may lock up while the trailer’s momentum keeps it moving forward. This difference in inertia causes the trailer to swing out.

Trailers with no brakes or ineffective brakes are especially prone to jackknifing during hard braking. The tractor slows down, but the trailer doesn’t, increasing the likelihood of a jackknife. Proper brake maintenance and inspection is essential to help prevent this.

Turning and Jackknifing

Inertia again comes into play when making turns. The trailer has the tendency to continue moving straight while the tractor turns. If turned too sharply, the momentum of the trailer can overwhelm the truck and cause it to jackknife. This risk increases with larger turning angles.

The length of the tractor-trailer also affects turning. The longer the vehicle, the wider the turning radius needed. Turning too sharply for the vehicle’s length can lead to a jackknife. Drivers need to take care and slow down for turns, especially with longer vehicles.

Road Conditions

Slippery road conditions are another jackknifing hazard. Ice, snow, rain, gravel, or other slippery surfaces reduce tire friction. With less grip, it’s easier for the tires to lose traction during braking or turning. This increases the likelihood of trailer inertial swing.

High speeds are dangerous on slick roads because they reduce the response time available to correct a jackknife. Slower speeds on slippery surfaces allow drivers more time to react and prevent a jackknife situation.

How to Prevent a Jackknife

To avoid jackknifing, drivers need to be aware of conditions and proactive in their driving. Some tips include:

  • Brake early and gradually to avoid abrupt speed changes. Slamming on the brakes can cause the trailer to push forward on the tractor, initiating a jackknife.
  • Take turns slowly and widely, especially with longer vehicles. The wider the turning radius, the less likely inertia will swing the trailer outward into a jackknife position.
  • Reduce speed for wet, icy, or snowy roads. Lower speeds give you more time to react and correct sliding on slippery surfaces before a jackknife occurs.
  • Correct sliding early before it leads to jackknifing. At the first sign of trailer sway or wheel slide, carefully steer in the direction of the slide to regain control.
  • Keep loads balanced and not too heavy in the rear. An overloaded or poorly distributed trailer is more likely to swing out under braking or turning due to a high center of gravity.
  • Maintain good tire tread for maximum friction. Worn tires have reduced grip, making it easier for them to lose traction and lead to jackknifing situations.

While jackknifing involves physics principles like inertia and friction, it also requires focus, skill, and care from drivers. Being aware of road and vehicle conditions at all times is key to preventing this deadly maneuver. Caution and quick reactions can help keep tractor-trailers and trucks pulling trailers safely on the road.

If you are injured in a jacknife accident caused by someone else’s negligence, a personal injury attorney from our firm can help you seek fair compensation. We investigate your claim, determine liable parties, estimate damages, negotiate settlements, and file lawsuits if needed. We can fight for maximum compensation while handling legal complexities for you. Retaining an experienced attorney protects your rights and interests.

Visit one of our offices below:

  • Beverly Hills – 8383 Wilshire Blvd, Suite 830, Beverly Hills, CA 90211
  • Los Angeles – 212 East Pico Blvd, Suite #4, Los Angeles, CA 90015
  • Tulare – 100 E. Cross, Suite #122, Tulare, CA 93274
  • Hanford – 13400 Hanford Armona Rd, Suite #B

Call now for a free consultation on (877) 729-2652 or (323) 782-9927.


Real Stories from Real People

They Put A Lot Of Their Time And Effort Into My Case.

Mr. Poursalimi and his team were truly professional. If you had a question, or you need a piece of information about anything on your case, they were there to tell you nothing but the truth about what you needed to know. They put a lot of their time and effort into my case to get fair compensation.

– Marala


Payam Is The Lawyer That You Want And Need.

If you are looking for an honest, friendly and professional law firm , look no further. Payam is the lawyer that you want and need for your personal injury case. He has extreme confidence in what he does that you know you will win the case no matter what.

– Amirsalar


Best Attorney Ever!

Best attorney ever! I was in a car accident by an uninsured motorist. I was extremely scared of the outcome but I was referred to Payam by my doctor and I couldn’t be more thankful! Payam and Ericka made the whole process so smooth and easy! They were very helpful! I would definitely recommend working with them.

– Annette A.




    The University of California UCLA
    Brain Society California
    Latlc Logo
    UWLA Logo
    Lead Council Verified
    TNTL Top 100
    CAALA Logo
    Super Lawyers