What Is Off Tracking? A Guide for Truck Drivers

What is Off Tracking?

What Is Off Tracking is the phenomenon where a vehicle’s rear wheels do not follow the same path as its front wheels when making a turn. This differential tracking is particularly significant in commercial trucks, tractor-trailers, and longer combination vehicles (LCVs) due to their extended length and multiple axles.

The magnitude of off-tracking generally increases with the spacing between the axles of the vehicle and decreases for turns with larger radii. For combination vehicles such as semi-trucks, the distance between the tractor kingpin and the center of the trailer’s rear axle group significantly impacts this behavior. Furthermore, in multi-trailer combinations, the effective wheelbase of all trailers along with the tracking characteristics of converter dollies dictate the degree of off-tracking.

Several factors affect how much a truck will off-track:

• Length of the vehicle (especially the trailer)
• Wheelbase dimensions
• Speed of the vehicle
• Radius and sharpness of the turn
• Axle loads and suspension characteristics

The maximum swept path of a truck is calculated as the combination of the vehicle’s width plus the distance the truck off-tracks. When this swept path exceeds the lane of travel, it creates significant safety hazards for other road users, including pedestrians, cyclists, and vehicles in adjacent lanes.

Off-tracking manifests in two distinct forms: low-speed and high-speed. Low-speed off-tracking occurs when a truck makes a turn at slow speeds, causing the rearmost wheels to follow a path several feet inside the path of the steering axle [11]. Conversely, high-speed off-tracking results from the lateral acceleration of the vehicle during turns at higher speeds, causing the rear of the truck to move outward.

For truck drivers, managing off-tracking requires specific techniques, especially when executing turns. During right turns, drivers often must pull approximately half the length of the truck past the corner before beginning the turn to avoid hitting curbs. Additionally, proper speed adjustment and gear selection before initiating turns are essential for safe maneuvering through intersections and curved roadways.

Types of Off-Tracking in Trucks

Trucks experience two distinct types of off-tracking as classified by the Federal Highway Administration (FHWA). These variations occur under different driving conditions and create unique challenges for commercial vehicle operators.

Low-Speed Off-Tracking

Low-speed off-tracking manifests when a combination vehicle executes a turn at reduced speeds, typically at intersections or tight corners. In this scenario, the wheels on the trailer’s rear axle follow a path several feet inside the track created by the front steering axle. This phenomenon becomes more pronounced as the distance between the tractor kingpin and the center of the trailer’s rear axle increases.

The effects of low-speed off-tracking are readily observable with Longer Combination Vehicles (LCVs). Professional drivers must compensate by swinging wide into adjacent traffic lanes, often to the left, in order to safely execute right-hand turns. According to research by Elefteriadou, a 45-foot semi-trailer negotiating a 90-degree turn requires at minimum a 30-foot curb return radius, while larger configurations such as Turnpike doubles need curb return radii exceeding 100 feet to avoid encroaching on opposing travel lanes.

High-Speed Off-Tracking

Contrary to its low-speed counterpart, high-speed off-tracking occurs when trucks navigate turns at elevated speeds, commonly on highways and freeway ramps. Rather than tracking inward, the rear wheels of the trailer swing outward from the tractor’s path. This outward movement results from the lateral acceleration forces acting on the vehicle during the turn.

Multiple factors determine the magnitude of high-speed off-tracking:

• Vehicle speed
• Spacing between truck axles
• Weight distribution of the trailer load
• Radius of the turn
• Suspension characteristics of the truck/trailer

As speed increases from very slow, the inside off-tracking gradually decreases until reaching a threshold speed where the rear trailer axles align perfectly with the tractor steering axle path. Above this threshold, the rear trailer axles begin tracking outside the path of the steering axle. This behavior creates substantial risk as trailers may drift into adjacent lanes, potentially striking properly positioned vehicles in neighboring travel paths.

What Causes Off-Tracking in Trailers?

Several factors contribute to trailer off-tracking, creating hazardous conditions that require proper management and awareness from truck operators.

Inexperienced or distracted driving

Driver inexperience substantially increases off-tracking risks, as novice operators often lack crucial skills for handling complex truck movements. New truck drivers show higher crash rates and moving violations during their first year. Distracted driving further amplifies these dangers, with drivers using cell phones having reaction times approximately 30% longer. Consequently, distracted drivers navigate at slower speeds and leave larger intervals between vehicles, adversely affecting traffic flow.

Improper cargo loading

Unbalanced or unsecured cargo creates serious stability issues that intensify off-tracking. When weight distribution is improper, the truck’s center of gravity shifts, making it difficult to control during turns. An unevenly loaded trailer becomes more susceptible to rollovers, jackknifing, and cargo shifts—especially when negotiating sharp turns or uneven terrain. Moreover, overloaded trailers dramatically increase the risk of off-tracking incidents.

Turning too fast or too sharply

The physics of making turns with a 70-foot tractor-trailer creates unavoidable swing patterns. A truck executing a 90-degree right turn can have its trailer track 6-12 feet inside the tractor’s path. Sharp turns at unsafe speeds can cause load shifts or rollovers, necessitating careful speed adjustment before entering turns. Professional drivers must shift into the proper gear before beginning the turn to maintain control.

Fatigue or impaired driving

Driver fatigue is a leading cause of heavy truck accidents, responsible for 13% of crashes annually. The Federal Motor Carrier Safety Administration reports that fatigue contributes to thousands of commercial vehicle accidents each year. Studies indicate that driving for 17 hours without sleep produces impairment equivalent to a blood alcohol level of 0.05. This fatigue severely impacts reaction time, concentration, and decision-making abilities.

Incorrect braking or gear shifting

Proper gear selection before initiating turns prevents the need for shifting during the maneuver. This allows drivers to keep both hands on the steering wheel throughout the turn. If a driver shifts while turning or accelerates into the turn, the risk to other motorists increases. Incorrect braking techniques can lead to jackknife situations during turns, occurring when the trailer and tractor form an acute angle.

FAQs

Q1. What exactly is off-tracking in truck driving? Off-tracking occurs when a truck’s rear wheels follow a different path than its front wheels during turns. This phenomenon is more pronounced in longer vehicles like tractor-trailers and can pose safety risks if not properly managed.

Q2. How does vehicle length affect off-tracking? The longer the vehicle, especially the trailer, the more significant the off-tracking effect. Increased spacing between axles and a greater distance from the tractor kingpin to the trailer’s rear axle center amplify this behavior.

Q3. What are the two main types of off-tracking? There are two primary types: low-speed off-tracking, where rear wheels track inside the front wheels’ path during slow turns, and high-speed off-tracking, where the trailer’s rear swings outward during faster turns on highways or ramps.

Q4. How can truck drivers minimize off-tracking risks? Drivers can reduce off-tracking risks by adjusting speed before turns, selecting the proper gear, avoiding distractions, ensuring balanced cargo loading, and maintaining alertness to combat fatigue.

Q5. Why is proper cargo loading important in preventing off-tracking? Proper cargo loading ensures weight distribution remains balanced, maintaining the truck’s center of gravity. This balance is crucial for stability during turns, reducing the risk of rollovers and excessive off-tracking, especially in sharp turns or on uneven terrain.