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Towing load, drawbar load, D-value for a towbar coupling

Meaning, calculation and their importance

Welcome to TOWBARS-Online, your comprehensive guide to towbars and their load values. If you want to tow a trailer, caravan or trailer with your vehicle, it is crucial not only to know the terms towing load, drawbar load and D-value, but also to understand their meaning and calculation. These values are essential for safety on the road and compliance with legal regulations. In this article, we explain these key concepts and why they are so important.

Angaben auf dem Typenschild einer Anhängerkupplung

Towing load: pulling the maximum load

The towing load, also known as trailer load, refers to the maximum weight that a vehicle is allowed to tow. This value is not arbitrary, but is set by the vehicle manufacturer based on the design and performance of the vehicle. Knowing the maximum towing capacity of your vehicle is crucial to avoid overloading, which can lead to increased wear and tear, accidents or legal problems.

Zuglast, auch Anhängelast bei AHK

Drawbar load: The pressure point between towbar and coupling

The drawbar load is the weight carried directly by your vehicle’s towbar. A correctly set drawbar load ensures a stable and safe journey by helping to balance the towing vehicle and the trailer. Too little drawbar load can cause the trailer to wobble, while too much drawbar load can negatively affect the handling of the towing vehicle.

Stützlast: Der Druckpunkt zwischen Anhänger und Kupplung

D-value: The measure of dynamic load

The D-value is a technical parameter that indicates the maximum permissible dynamic load of a towbar. It is expressed in kilonewtons (kN) and is an indicator of how much tractive force the coupling can safely transmit. The calculation of the D value is based on the total weight of the vehicle and the trailer as well as the acceleration due to gravity:

D = (G × R × 9.81) / (G + R)

G is the gross vehicle weight rating of the towing vehicle,

R is the permissible gross weight of the trailer.

Further down in the text you will find a practical calculator for calculating the trailer load and the parameter D.

D-Wert: Das Maß für die dynamische Belastung

Why are these values so important?

Correctly setting and maintaining the drawbar load, drawbar load and D-value are crucial for several reasons:

  • Safety: adhering to these values ensures a stable ride and minimises the risk of accidents.
  • Legal regulations: Overloading and incorrect load distribution can lead to fines and vehicle confiscation.
  • Vehicle integrity: Observing the values specified by the manufacturer protects your vehicle from damage.


Knowing and observing the towing capacity, drawbar load and D-value is essential for anyone operating a vehicle with a trailer. Not only from a legal point of view, but above all in the interests of safety. So before you hit the road next time, make sure that your vehicle and trailer are loaded correctly and that all relevant load values are adhered to. Stay safe and informed with TOWBARS-Online.

Anhängelast Berechnung anhand D-Wert und Gesamtgewicht

Trailer load calculation

function calculateTrailerLoad() { var dwertInput = document.getElementById('dwertInput').value; var vehicleWeightInput = document.getElementById('vehicleWeight').value; // Check whether the inputs are empty if (!dwertInput || !vehicleWeightInput) { document.getElementById('resultLoad').innerHTML = "Please fill in all fields."; return; } var dwert = parseFloat(dwertInput); var vehicleWeight = parseFloat(vehicleWeightInput); // Check if the values are positive if (dvalue <= 0 || vehicleWeight <= 0) { document.getElementById('resultLoad').innerHTML = "Please enter valid, positive values."; return; } var trailer load = dvalue * (vehicle weight / 9.81); var precision = 0.0001; // Desired accuracy of the solution var estimate = trailer load; // Starting estimate for the iterative calculation while (true) { var newEstimate = (dvalue * 1000 * (vehicleWeight + estimate)) / (9.81 * vehicleWeight); if (Math.abs(newEstimate - estimate) < accuracy) { break; } estimate = newEstimate; } document.getElementById('resultLoad').innerHTML = "The calculated attachment load is: " + estimate.toFixed(2) + " kg"; }

D value calculation for trailer coupling

function calculateValue() { var totalweightInput = document.getElementById('totalweight').value; var appendlastInput = document.getElementById('appendlast').value; // Check whether the inputs are empty or invalid if (!total weightInput || !trailer loadInput) { document.getElementById('result').innerHTML = "Please fill in all fields."; return; } var total weight = parseFloat(total weightInput); var appendload = parseFloat(appendloadInput); // Further checking whether the numbers entered are positive if (total weight <= 0 || trailer load <= 0) { document.getElementById('result').innerHTML = "Please enter positive values."; return; } var dValue = (total weight * trailer load * 9.81/1000) / (total weight + trailer load); document.getElementById('result').innerHTML = "The D value is: " + dValue.toFixed(2) + " kN"; }
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