The D-value is an indication of the strength of a towbar. It can be calculated using the following formula:
D = G(K) x G(A) x 9.81
G(K) + (A)
Where G(K) is the gross weight of the towing vehicle in tonnes and G(A) is the gross weight of the trailer, also in tonnes. For example, a Fiat Ducato with 3.5t gross weight and towing capacity of 2t requires a towbar with a minimum D value of:
D = 3.5 x 2.0 x 9.81 = 12.50 kN
3.5 + 2.0
The actual permissible trailer load is based on the value stated in section 28 or 01 of the vehicle registration documents. Of all the given values it is always the lowest value that should be adhered to.
