Whether you’re towing a caravan, trailer, or camper, knowing your vehicle’s weight limits is key to towing safely, legally, and with confidence.
One weight you must know is your D-value.
Here is a simple guide on what D-value is and how ensure that you are not overloaded.
What is D-Value
What “D-Value” Stands For
In the towing industry, “D-Value” (Downward Value) is a force that refers to a towing component’s “dynamic load capacity“.
So what does dynamic load capacity mean? A dynamic load capacity is the maximum force that can be safely supported by a towing part when a vehicle is subject to movement, such as when a vehicle is driving.
This is different to a static load capacity, which is the maximum recommended force which can be applied while a vehicle is stationary.
D-Value Simplified
Basically, your D-value tells you how much force can be transferred to the towbar without the trailer becoming unstable.
Once the downward force is higher than your towing part’s recommended D-Value, there can be some serious consequences.
The Consequences of Going Over Your D-Value
Loss of Control and Handling
When there is too much force going down on your towball, the back of your car and the front of your towing vehicle tilt toward the road.
With the front of your car in the air, you can no longer steer.
Hitch and Connection Risks
Wheel/Tyre Overload and Tyre Blowouts
Too much downward force on your towball can lead to too much force on your tyres, and the chance of a tyre blowout.
Not a good thing to experience when on a nice holiday.
Increase in Braking Distance
Transmission and Engine Strain
Is D-Value Different for Dual Axles or Tri-Axles
What Towing Parts Have a D-Value?
D-values start to apply once the towing component application exceeds a 3500 kilogram ATM.
A key piece of information is that, if a company only displays their static load capacity of their part, it is likely that they have not tested the product to an official standard to calculate the D-Value.
How to Calculate Your D-Value
In Transport, a D-value is a rating in kilo-newtons that is typically attributed to mechanical couplings, and reflects dynamic loading limits between a towing vehicle and a trailer.
The full equation that calculates your D-Value is:
D-Value = 9.81 x (Tow Vehicle GVM x Trailer ATM) divided by (Tow Vehicle GVM + Trailer ATM).
So, for example, a 12 tonne truck towing an 8 tonne trailer has a D-Value of 47Kn.
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