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Trailer / Caravan Stability

With such advances in vehicle technology, manufacturers have sought to develop a particular system which gives them the edge over their competitors. This is most apparent in on-board vehicle safety systems. In the 1980’s, we saw ABS become a selling feature for one or two manufacturers, this is now common place on 99% of vehicles on our roads.

Over the last few years we have seen other safety features such as Brake Force Distribution, Side Impact Bars, Rear Passenger Airbags, Curtain Airbags and so on.

The latest safety feature which is fast becoming a primary safety feature on virtually all new vehicles is the Electronic Stability Programme (ESP). This comes in various guises depending on the manufacturer. For Example, BMW call this DSC (Dynamic Stability Control), Toyota use the term VSC (Vehicle Stability Control). Advances in vehicle technology have enabled a number of other safety features to incorporate a trailer. See ‘Towing Safety Aids’ for more information.

How does TSP function?

When trailers or caravans start to sway dangerously, it is usually a result of the way of driving, speed, crosswinds, road condition and/or, a badly laden trailer or caravan. Caravans and horse box trailers present a special risk. When “snaking” occurs, many drivers display the wrong reaction and under stress, try to keep their tow vehicle and trailer on track by counter steering. This will only amplify the swaying effect and eventually result in an accident. The specific additional function of ESP, known as the Trailer Stability Program (TSP), recognizes swaying on the basis of the typical yaw rate in the tow vehicle. This allows for the right measures to be initiated at an early stage: the towing combination is slowed down to a non-critical speed by automatically braking all 4 wheels of the towing vehicle individually, whilst simultaneously reducing the engine speed and thus correcting the swaying movement. In most cases, providing the vehicle has been equipped a “Vehicle Specific Towbar Wiring Kit”, the additional software in the ESP module is activated as soon as the electrical connection cable of the trailer is plugged into the towbar socket.

How does ESP function?

The electronic stability program (ESP) is a further enhancement to the Anti-Lock Braking System (ABS) and Traction Control System (TCS). The ESP is designed to detect a difference between the drivers control inputs and the actual response of the vehicle. When differences are detected, the system intervenes by providing braking forces to the appropriate wheels to correct the path of the vehicle. This automatic reaction is engineered for improved vehicle stability, particularly during severe cornering and on low-friction road surfaces, by helping to reduce over-steering and under-steering. To implement ESP functionality, sensors must be added to the ABS system. A steering wheel angle sensor is used to detect driver input, with a yaw rate sensor and a low-G sensor that measure the vehicles response. Some ESP systems include a connection to the powertrain controller of the vehicle to enable reductions in engine torque when required.

How do I know if TSP is working?

When the vehicle detects a swaying motion caused by a “Snaking” trailer, the TSP system will start to correct the movement. The driver will be informed via a flashing ESP light on the instrument display. Note: Some vehicles equipped with this system will perform a firm braking action. It is recommended that whenever the TSP is correcting the trailer that the steering wheel is kept in a straight position, in order for the towing combination to be controlled.

The information contained on this page is based on independent research into current vehicle stability systems and therefore does not constitute any legally binding documentation. This video was produced for educational reasons only.

 Video Demonstration