The admissible total vehicle combination weight (currently 40 t) minus theadmissible total weight of tractor is the towed load.
Central axle trailer (C):
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.
Dc-Wert (valid only in connection with the V-value)
Calculation of the Dc-value in kN:
T: total weight of the towing vehicle in t
C: sum of the axle loads of the central axle trailer in t
g: gravitational acceleration 9,81 m/s2
The calculated Dc-value can be equal to or less than the Dc-value of the drawbar eye.
V-Wert (valid only in connection with the Dc-value)
Calculation of the V-value in kN:
a: an equivalent vertical acceleration in the hitch point in m/s2
a = 1,8 for vehicles with air suspension
a = 2,4 for vehicles with other suspensions
I: theoretical drawbar length in meters
x: length of the loading area in meters
x²/l²: at least 1,0
C: sum of the axle loads of the central-axle trailer in t
For approvals according to ECE R147 applies:
V (kN) = 1,8 . 1,44 . C
The calculated V-value can be equal to or less than the V-value of the hitch and of the towing eye.