## 1. Tractor weight - In the absence of the D-value:

The admissible total vehicle combination weight (currently 40 t) minus the admissible total weight of tractor is the towed load.

• Vertical load from the central axle trailer at the hitch point.
• The maximum possible static vertical load depends on the size of the hitch andamounts to 10 % of the total weight of the trailer or 1000 kg (which ever isless). Higher values are possible.
• The static vertical load should be at least 4% of the trailer weight in order toavoid a damaging negative vertical load.
• The level of the vertical load also depends on the speed.

Central axle trailer (C):

• Size of the central axle trailer depends on the characteristics of the drawbareye and the tractor unit.

## 3. D-value

D-value (not in all hitches)
Theoretical horizontal force between towing vehicle and trailer, comparative mathematical value of forces between two moving masses.
The D-value can only be calculated from the admissible total weight of both masses (towing vehicle and trailer).
Calculation of the D-value in (kN):

T: total weight of the towing vehicle in t

R: total weight of the turntable trailer in t

g: gravitational acceleration (9.81 m/s2)

The calculated D-value can be equal to or less than the D-value of the hitch (type plate) or the weakest link in the overall rig.

Where use of the hitch is permitted for the trailer:

R1: total weight of the trailer on which the coupling is mounted in t;

R1 ≥ R2

Hitches and drawbar eyes for road traffic which are tested pursuant to the European standard 94/20 also have specialcharacteristic values established for use with the central axle trailer, the Dc-value and the V-value.

## Towing vehicle and central-axle trailer: The Dc-value

• Theoretical horizontal force between towing vehicle and trailer, comparative mathematical value of forces between two moving masses
• The Dc-value can only be calculated from the admissible total weight of both masses (towing vehicle and trailer).
• Calculation of the Dc-value in kN:

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