A description on towball heights.
The position and height of the towball on your vehicle is not something that can be adjusted to suit individual caravan, trailer or other towing equipment. These factors have already been predetermined by manufacturers and the EC Directive 94/20/EC.
To measure the height of the towball, you measure from the ground to the centre of the towball. Note: when measuring the towball, the vehicle should be on level ground.
What is the EC Directive 94/20/EC?
The EC Directive 94/20/EC is the standards to which all towbars and couplings are designed, by manufacturers, to within Europe and the UK.
What height should couplings and towballs be?
As stated in the EC Directive, all towballs should be within 350mm and 420mm when the vehicle is in its laden state and that all couplings should be 385mm to 455mm in the caravans/trailers laden state. Laden state meaning either when the vehicle is fully loaded with passengers and luggage (see the vehicles homologation documents to see what weight was used for the laden state), or when a trailer is at its
maximum specified weight that is evenly distributed on its loading area. This does mean that when emptied of of passengers and luggage the towball/coupling will often be higher then 420mm/455mm.
Should the caravan/trailer be level when towed?
No, a common misconception people have is that a trailer chassis must be perfectly level while towing and will attempt to achieve this. However, as stated above, it is normal to have up to 105mm difference between the coupling and the towball when in laden states and up to 500 mm difference when at lower weights.
Towball too high or too low?
If you think the towball is too high or too low on your vehicle, firstly you should measure it. If it's within the range stated above, then it is correct and any issues may lie with the coupling you are using. As long you have no grounding or stability issue, there is no technical reason to alter the height. If it is necessary, with an EC type approved towbar, there are a few options.-
Some vehicles, not all, have multiple towball fixing heights, so you could try a different towball location.
Check your vehicles suspension for any wear and tear, or if you have you have a sport suspension the vehicle could be to low for the towball.
Consider modifying the height of the coupling.
Is there an issue with the jockey wheel grounding, can it be repositioned.
Some towbars, not all, are EC type approved to have a drop plate.
Can I use raiser plates?
Under no circumstances should the towball height be raised outside of the range stated above. In doing so, the increased leverage on the towbar and towball interface could result in damage or failure to one or more of the towing system components. It will also invalidate the EC approval of your towbar.