What height should the towball be?
The EC Directive 94/20/EC (The standard that all towbars are designed to) says that the tow ball height should be between 350 and 420mm from the ground with the vehicle in a 'laden' state.
The 'laden' state means when the vehicle is loaded with passengers and luggage which means that when the car is empty of passengers and luggage, the towball can end up being higher than 420mm.
How to measure towball height
Tow ball height is measured as the distance between the ground and the centre of the towball.
It is important to make sure your car is parked on level ground when taking the measurement.
What height should a trailer/caravan coupling be?
The EC Directive states that this should be 385 to 455mm with the trailer in the 'laden' condition.
'Laden condition' in this instance is when the trailer is loaded to its maximum specified mass, with this evenly distributed over the loading area.
Should the trailer or caravan be level while towing?
Not always! A lot of people think that it is essential to have the trailer chassis level. However as can be seen by whats mentioned previously it can be seen that there is inherently a wide height range for both the towballs and the trailer couplings.
Also, the specifications are written to promote a tendency towards a slightly 'nose down' driving position of the trailer, with the medium of the range for the trailer being 35mm higher than the medium of the height range of the towball on the towing vehicle.
Furthermore from the permissible ranges and laden definitions it can be seen that the difference can be extreme e.g.
- Towball at 350mm (fully laden vehicle) and trailer coupling at 520mm (not untypical of an unladen trailer)... a difference of 170mm!
- Towball at 510mm (unladen long suspension travel vehicle) and 385mm trailer coupling height (for fully laden trailer)... a difference of 125mm!
The situation is further complicated by the fact that the towbar/towball is controlled by an EC directive.
What can I do if my tow ball is too low?
This depends on what has caused this. Possibly the towball is in the correct height range and the trailer coupling height is incorrect. For some reason, this is automatically thought of as a 'fault' of the vehicle/towbar – please measure and check!
Unless there is a grounding or a stability problem there is no technical reason to do anything in this instance.
However if it is necessary, with an EC type approved towbar the options are:
- Use a different towball location (some vehicles may have two or more different towball fixing heights).
- Check the vehicle suspension.
- Are spring assisters or suspension changes or adjustments possible?
- Modifying the trailer coupling height should be considered.
- If the issue is the jockey wheel grounding, reposition this.
- If the vehicle has sports suspension often 15-50mm lower than standard models? Please check against the chassis number with the Dealer.
What can I do if my tow ball is too high?
You will be limited to these following options:
- Use a different towball location (some vehicles have two or more )
- Consider using a drop plate (some towbars are tested and EC type approved for use with drop plates – check the towbar installation instructions).
- Alternatively, if it is a commercial vehicle the tow bar is on its currently not mandatory to have an EC compliant towbar and it may be possible to use a drop plate (but always check with the towbar manufacturer).
Can I use a raiser plate?
No, under no circumstances use a raiser plate, it could result in damage or failure of one of the towing system components and invalidate any EC approval of the towbar.