# D-Value (Articulated Truck/Towed Trailer Coupling) Calculation formula The so-called D-value has been defined to determine the load capacity of trailer couplings (D = drawbar).

The so-called D-value has been defined to determine the load capacity of trailer couplings (D = drawbar). It applies equally to articulated truck and towed trailer couplings, but is differently calculated. The D-value is stamped into the type plate on a trailer coupling. Its unit is kN. The D-value can be calculated from the permissible total mass of the towing vehicle and trailer. The higher the D‑value, the greater the mass that can be attached to a coupling.

### Trailer coupling (D-value)

The D-value for a towing vehicle/ trailer combination is calculated as per the following formula: Calculation factors:
g is gravity and  = 9,81 m/s
mZ is the permissible total mass of the towing vehicle [t]
mA is the permissible total mass of the trailer [t]

### Articulated truck coupling (D-value)

The D-value formula for an articulated truck is: Calculation factors:
g is gravity and = 9,81 m/s2
mZ is the permissible total mass of the towing vehicle [t]
mA  is the permissible total mass of the trailer [t]
S is the permissible vertical load [t]

### Example

A towing vehicle with a permissible total mass of
mZ = 18 t and a trailer with the permissible total mass of von mA = 14 t are connected to each other by an automatic trailer coupling. What is the minimum D‑value for the trailer coupling? A tractor unit with a permissible total mass of
mZ = 16 t and a maximum vertical load of S = 8 t is pulling a trailer with the permissible total mass  mA= 16 t. What is the minimum D‑value for the articulated coupling? 