• D-value Fifth wheel dolly
  • D-value Truck and trailer
  • Dc-value Central-axle trailer
  • V-value Central-axle trailer

D-value Fifth wheel dolly

D-value Fifth wheel dolly

Definition D value

The construction of the fifth wheel coupling in connection with the vehicle is carried out by the vehicle manufacturer (construction according to Directive ECE-R55, Appendix 7).

The imposed load on the tractor and the D value are criterions for the load-bearing capacity of the fifth wheel couplings and mounting plates.

D = (g * 0.6 * T * R) / (T + R - U)

The permissible load data for JOST fifth wheel couplings can be found on the type plate or from the JOST product catalogue. They apply for the intended use in compliance with the Directive ECE-R55, Appendix 7.

If additional dynamic demands are to be placed on the coupling, e.g. by use on uneven road surfaces or building sites, the imposed load and D value should not be fully used or a stronger fifth wheel coupling should be fitted, and/or you should ask JOST for advice.

T =
R =
U =

permissible total weight of the tractor unit in t (including U)

permissible total weight of the semi-trailer in t

permissible imposed load on tractor in t

Fifth wheel dolly:
GVW:


D-value Truck and trailer

D-value Truck and trailer

Truck and trailer: D-value

• Theoretical horizontal force between towing vehicle and trailer
• The D-value can only be calculated with the permissible total weight of both truck and trailer
• Calculation of the D-value (kN):

D(kN) = (g * T * R) / (T + R)

The calculated D-value can be equal to or lower than the D-value of the hitch and of the towing eye.

T =
R =

total weight of the towing vehicle in t

total weight of the drawbar trailer in t

D-value (kN):
GVW:


Dc-value Towing vehicle and central-axle trailer

Dc-value: Towing vehicle and central-axle trailer

Towing vehicle and central-axle trailer: Dc-value

Valid only in connection with the V-value
• Theoretical horizontal force between towing vehicle and trailer
• The Dc-value can only be calculated with the permissible total weight of both truck and trailer
• Calculation of the Dc-value (kN):

(kN) = (g * T * C) / (T + C)

Dc-value can be equal to or lower than the Dc-value of the hitch and of the towing eye.

T =
C =

total weight of the towing vehicle in t

sum of the axle loads of the central-axle trailer in t

Dc-value (kN):
GVW:


V-value Central-axle trailer

V-value: Central-axle trailer

Central-axle trailer: V-value

Valid only in connection with the Dc-value
• Vertical force for central-axle trailer
• Dependent on the rear axle suspension of the towing vehicle
• Calculation of the V-value (kN):

V(kN) = (a * x2 * C) / L2

Central-axle trailer: Static vertical load S only valid in connection with the V-value

• Vertical load of the central-axle trailer on the hitch point
• The vertical load depends on the size of the hitch and the maximum is 10% of the gross weight of the trailer or 1000 kg (whichever is less).
• When using a central-axle trailer the vertical load should amount to at least 4% of the trailer weight in order to prevent increased wear caused by bouncing of the towing eye.

a =
l =
x =
C =

an equivalent vertical acceleration in the hitch point in m/s2. 1,8 m/s2 for vehicles with air suspension. 2,4 m/s2 for vehicles with other suspensions.

theoretical drawbar length in meters

length of the loading area in meters. x2/l2 : at least 1,0

sum of the axle loads of the central-axle trailer in t

V-value (kN):
GVW: