How is towball height measured?

Towball height is calculated by measuring from the ground to the centre of your towball. Although most surfaces are uneven, the ground needs to be flat and level to get the correct measurement for the towball height. The coupling height also needs to be taken into account. The condition of the vehicle when laden or the position of the towball’s centre while situated within the coupling head should be considered.

What is the correct towball height?

This is a tricky one to answer! EC Directive 94/20/EC stipulates that a vehicle in ‘laden condition’ should have a towball height of between 350mm and 420mm. The vehicle’s manufacturer could define ‘laden condition’ as ‘fully laden’. This is the maximum permitted mass of a vehicle as specified in the vehicle’s handbook.
On the other hand a manufacturer may define ‘laden condition’ as ‘conventionally laden’. This is when a load of 68.5 kg is permitted for each specified passenger seat, along with a further 6.5 kg allocated per passenger and located centrally in the area for luggage storage. You will need to check which specifications apply to your particular towing vehicle.

What is the correct height for the coupling head on a trailer or caravan?

A height of 385mm to 455mm is stipulated by the EC Directive if the trailer or caravan is in laden condition. Laden condition refers to a trailer loaded to the maximum specified mass in this instance. The mass must also be distributed evenly over the loading area.

Does my caravan or trailer need to be level?

Many people think that their trailer chassis must be completely level , but luckily, this is not the case. As we have already seen, the height range for trailer couplings and towbars can vary. The specifications are intended to ensure that the trailer/caravan’s attitude is somewhat ‘nose down’. The trailer’s medium range is 35mm higher than the towball’s height range (on the towing vehicle).

Once again this is not straightforward, because the permissible ranges and definitions of a vehicle’s ‘laden condition’ can vary considerably.
The difference between a towball height of 350mm and a vehicle (fully laden) with a coupling height of 510mm on an unladen caravan or trailer is 170mm.
The difference between a towball height of 510mm on a long suspension travel vehicle and a fully laden caravan or trailer with a coupling height of 385 will be 125mm.
However, while the towball and towbar fall under an EC Directive, the caravan or trailer does not have to be EC approved. This can complicate the situation.

What can I do if my towball is too low?

Your towball could be within the permitted height range already if the trailer coupling is at the incorrect height. It is always worth measuring this! If stability and grounding are fine you do not need to do anything.

If there are issues, you have a number of options with an EC Type Approved towbar:
•    If you have a vehicle that has more than two towball fixing heights the towball location can be changed
•    Consult the towbar fitter to see if it is possible to retighten or loosen any components and check that towbar is correctly installed
•    Vehicle suspension might be the culprit if the suspension has settled or worn. Adjustments might be possible if this is the case
•    The trailer coupling height could be modified. Sometimes the jockey wheel grounding is the culprit, so this can be repositioned
•    Sports’ suspension is usually 15mm to 50mm lower than other models. If your vehicle has sports suspension this can be verified by the dealer who will know the chassis number

What can I do if my towball is too low?

The caravan or trailer may not be compliant, so it is worth measuring and checking this. If this is not the case there are several options for EC Type Approved towbars:

•    If the vehicle has more than two towball fixing heights the towball position can be changed
•    A drop plate could be employed. The towbar must be one that has been Type Approved for use with drop plates. This can be checked on the installation instructions for the towbar
•    It is not mandatory for commercial vehicles to be fitted with EC compliant towbars. A drop plate could solve the problem, but it is a good idea to get advice from the towbar’s manufacturer

What about using a ‘raiser plate’ to increase towball height?

No, because there is a significant risk of causing damage to towing system components which may cause failure. Using a raiser plate causes the leverage on the towball/towbar interface to increase.
This would almost certainly result in an invalidation of the towbar’s EC Type approval! Instances where a raiser plate can be used are few and far between. Written permission must be sought from the towbar’s manufacturer. The use of a raiser plate is limited to special circumstances where a pin and jaw are raised into position in place of a towball.