0105 - Trailer couplings A. General

31.5-105 Trailer couplings

A. General

Towing vehicle and drawbar trailer

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D-value (drawbar value)

In determining the size of the trailer coupling, the hole pattern according to DIN 74051 or DIN 74052 in the rear cross member is to be taken into account.

The D-value formula also provides information on the required size of trailer coupling. The D-value (drawbar value) is a theoretical comparative value of forces occurring between moving masses. The D-value is not to be confused with a trailer load.

The permissible D-value is calculated from:

D = g . mK . mA

mK+mA

mK : Total weight of towing vehicle in t

mA : Total weight of trailer in t

g : Gravitational constant (9.80665 m/s2)

D : Drawbar value (kN)

Level of D-value according to size of trailer
coupling (in accordance with DIN):

Tow vehicle and central axle trailer

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On vehicle combinations with central axle trailer (rigid drawbar trailer; axle or axle group arranged centrally; single-axle vehicles, tandems or triples) the trailer load for central axle trailers specified on the maker's plate of the trailer coupling and that for the truck must not be exceeded.

In determining the size of the trailer coupling, the hole pattern in accordance with DIN 74051 or DIN 74052 in the rear cross member is to be taken into account.

The permissible total weight and the vertical coupling load of the central axle trailer (refer to maker's plate of the central axle trailer) determine the required size of trailer coupling. Approval of the size of the trailer coupling for the truck is to be taken into account. Should an increase in trailer load be required, the truck body guidelines are to be complied with.

Information is provided under the designations "vertical coupling load" and "permissible trailer load of central axle trailers" on the maker's plate.

The following relationship applies:

Specifications on Specifications in

the maker's plate the vehicle

of the trailer coupling registration document of the trailer

Vertical coupling load +

permissible trailer

load = permissible total weight of central axle trailer

Example:

700 kg + 6 500 kg = 7 200 kg

Assignment of trailer load and vertical coupling load to size of trailer coupling (in accordance with DIN):

Permissible static vertical coupling load

To increase the driving stability the maximum possible vertical coupling load should act on the trailer coupling. The permissible vertical coupling load of the truck is to be taken into account (ABE specifications).

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Always avoid negative vertical coupling loads (acting upwards).

Pivot angle of trailer couplings

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Trailer couplings must maintain the minimum pivot angle in accordance with DIN.

In accordance with DIN these are:

Axial pivot angle  25° about the longitudinal axis to the horizontal plane (a) of the vehicle.

1 Coupling pin

2 Towing eye

Vertical pivot angle  20° about the transverse axis to the horizontal plane (a) of the vehicle.

1 Coupling pin

2 Towing eye

Horizontal pivot angle  90° about the perpendicular axis to the longitudinal axis (b) of the vehicle.

1 Coupling pin

2 Towing eye

DIN standards

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There are two DIN standards for trailer couplings in the field of application of the StVZO [Federal Motor Vehicle Safety Standards] (agricultural use excluded).

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Towing eyes may only be coupled in accordance
with the relevant DIN standard, refer to the
following table: