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Other conditions apply for the rigid drawbar and central axle trailers in addition to the D value. Trailer couplings and end cross members have lower trailer loads because in this case the nose weight acting on the trailer coupling and the end cross member has to be taken into account.

In order to harmonize the regulations within the European Union, the terms Dc value and V value were introduced with Directive 94/20/EC.

The following formulae apply:

Dc value formula for rigid drawbar and central axle trailers

Dc = ( G · T · C ) / ( T + C )

V value formula for central axle and rigid drawbar trailers with a permissible nose weight of ≤ 10% of the trailer mass and not more than 1000 kg

V = a · x2 / I2 · C

If the values for x2 / l2 have been calculated as < 1, a value of 1.0 is to be used.

Where:
Dc = Lower D value when operating with a central axle trailer, in kN
T = Permissible gross weight of the towing vehicle, in metric tons
C = Sum of the axle loads of the central axle trailer loaded with the permissible mass, in t, not including nose weight S
V = Applied force on coupling and tow ball, V value, in kN
a = Reference acceleration in the coupling point, in m/s2. Two values are to be used: 1.8 m/s2 for air suspension or comparable suspension on the towing vehicle, and 2.4 m/s2 on all other vehicles
x = Length of trailer body, see Figure 1
l = Theoretical drawbar length, see Figure 1
G = Gravity, m / s2 Figure 1