Most towing equipment introduced since 1998 should be type approved and have a plate or sticker showing:
The Manufacturer
The country of Type Approval (eg E11)
The part number
The Eu standard (typically A50-X)
The ‘S’ Value
the ‘D’ Value.
As users, the 2 most important bits of information are the ‘S’ value and the ‘D’ value.
The ‘S’ value is straightforward. Simply, it is the maximum vertical load (nose-weight) that can be imposed on it. It’s measured and shown in kilograms and typically might be between 50 -150 Kgs. Higher values are permissible on certain equipment but, for the purposes of this blog, it’s restricted to regular use such as a Motorhome owner or a car/van driver towing his/her Cat01 or Cat02 trailer on a standard 50mm tow-ball. (Trailer category info is for another blog).
The ‘D’ value is a little more complex. Towing equipment isn’t generally rated by a finite value (i.e. 1500kgs) but by a ‘D’ value calculation. The capacity of the towing equipment will vary, dictated by the GVW (Gross Vehicle Weight) or MAM (Maximum Authorised Mass) of the towing vehicle. As the vehicle’s GVW or MAM goes up, it’s towing capacity will go down if the ‘D’ value is fixed.
‘D’ value of the towing equipment needs to be at least high enough to accommodate the vehicle’s maximum towing capacity as calculated from the VIN plate.
Here we have the VIN plate from a Vauxhall Vivaro Van.
The info on the VIN plate shows a towing limit of
exactly 2 tonnes (fully laden) . That is the Gross
Vehicle weight (1st weight displayed) deducted
from the Gross Train Weight (2nd weight
displayed).
To be compliant, the ‘D’ value of the towing
equipment needs to accommodate both the van’s
GVW (MAM) and it’s maximum towing limit.
So How Do We check it’s Adequate?
Use the calculation:
D value = 9.81 x (towing vehicle’s GVW x Trailer’s MAM) / (towing vehicle GVW + Trailer’s MAM)
In this case, 9.81 x(3.03(tonnes)
x 2(tonnes)) / (3.03(tonnes) + 2(tonnes)) = 11.82 D value.
As the tow-bar is plated at a D value of 12.02, it’s a
perfect match! :)
NOTE! It is ILLEGAL to exceed ANY of the weights on the VIN plate, or the towing equipment’s nose-weight (in this case 85Kgs.)
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