## Hitch / Drawbar eye / calculation

## 1. Tractor weight – In the absence of the D-value:

The admissible total vehicle combination weight (currently 40 t) minus theadmissible total weight of tractor is the towed load.

## 2. Vertical load - Static vertical load

- Vertical load from the central axle trailer at the hitch point.
- The maximum possible static vertical load depends on the size of the hitch andamounts to 10 % of the total weight of the trailer or 1000 kg (which ever isless). Higher values are possible.
- The static vertical load should be at least 4% of the trailer weight in order toavoid a damaging negative vertical load.
- The level of the vertical load also depends on the speed.

**Central axle trailer (C):**

- Use admissible in principle:
- Size of the central axle trailer depends on the characteristics of the drawbareye and the tractor unit.

## 3. D-Value

## 3. D-value

**D-value** (not in all hitches)

Theoretical horizontal force between towing vehicle and trailer, comparative mathematical value of forces between two moving masses.

The D-value can only be calculated from the admissible total weight of **both** masses(towing vehicle **and** trailer).

**Calculation of the D-value in (kN):**

T: total weight of the towing vehicle in t

R: total weight of the turntable trailer in t

g: gravitational acceleration (9.81 m/s^{2})

The calculated D-value can be **equal to or less** than the D-value of the hitch (type plate) or the weakest link in the overall rig.

**Where use of the hitch is permitted for the trailer:**

R1: total weight of the trailer on which the coupling is mounted in t;

R1 ≥ R2

Hitches and drawbar eyes for road traffic which are tested pursuant to the European standard 94/20 also have specialcharacteristic values established for use with the central axle trailer, the **Dc-value** and the **V-value.**

## 4. Towing vehicle and central-axle trailer: The Dc-value and V-value

**Dc-Wert **(valid only in connection with the V-value)

- Theoretical horizontal force between towing vehicle and trailer, comparative mathematical value of forces between two moving masses
- The Dc-value can only be calculated from the admissible total weight of
**both**masses (towing vehicle**and**trailer).

**Calculation of the Dc-value in kN:**

T: total weight of the towing vehicle in t

C: sum of the axle loads of the central axle trailer in t

g: gravitational acceleration 9,81 m/s^{2}

The calculated Dc-value can be **equal to or less** than the Dc-value of the drawbar eye.

**V-Wert **(valid only in connection with the Dc-value)

- Vertical force for central-axle trailer
- Dependent on the rear axle suspension of the towing vehicle

**Calculation of the V-value in kN:**

a: an equivalent vertical acceleration in the hitch point in m/s2

a = 1,8 for vehicles with air suspension

a = 2,4 for vehicles with other suspensions

I: theoretical drawbar length in meters

x: length of the loading area in meters

x²/l²: at least 1,0

C: sum of the axle loads of the central-axle trailer in t

For approvals according to **ECE R147** applies:

**V (kN) = 1,8 . 1,44 . C**The calculated V-value can be

**equal to or less**than the V-value of the hitch and of the towing eye.