Caravan Tow Ball Weight - how much
Tow Ball Weight Definitions
Tow ball weight is the weight placed on the tow ball (or other coupling device) of a tow vehicle via the tow hitch of a trailer. This weight is technically known as tow ball mass - but for the purpose of this article, mass and weight may seen as meaning the same thing.
Both vehicle manufacturer and tow hitch manufacturer set a maximum tow ball weight. The law requires you use whichever is the least.
The acceptable tow ball weight for many tow vehicles continues to be lowered. This is because emission regulations continue to tighten - and vehicle emissions relate to weight. As a result (regardless of a tow vehicle's rugged looks) its chassis, suspension, axles and tyres may not be designed to tow heavy loads. See the maximum tow ball masses of some popular tow vehicles here.
Trailer manufacturers, however, usually recommend the tow ball weight which the trailer should place on the tow vehicle. This usually expressed as a percentage of the trailer's laden weight (e.g. 10%) and is vital for trailer stability. In reality, however, trailer length is also involved. A long heavy trailer needs far more tow ball weight than a short trailer of the same weight.
Why the Need for Tow Ball Weight
That a caravan be nose heavy is vital for safe towing. A billiard cue thrown light-end first rapidly changes ends: it continues heavy-end first. Unless caravans are nose heavy they’ll attempt to do the same.
There is a proven relationship between tow ball weight and the speed at which major instability occurs. The lower the tow ball weight the lower the rig's stability. Tow ball weight, however, usually has to be a compromise. As the nose weight pushes down on the rear of the tow vehicle it levers up its front. This reduces the weight on the tow vehicle's front wheels and degrades the rig's cornering and braking ability.
In the unlikely event of nose weight being too high, the caravan seems ultra-stable, but will be reluctant to move in any but a straight line. This can result in emergency swerving being impossible, and equally to cease swaying if a strong sideways force is imposed.
Caravan Weight Distribution
A caravan should be designed to have the optimal recommended tow ball mass when laden. Tow ball weight, however, is also affected by the weight and location of the caravan's payload, mainly water and your personal effects).
A caravan's weight, including payload, should be as central as possible. The heavier loads should close to or over the axle(s) and low down. Ideally, the A-frame should carry no load. Most importantly, nothing heavy should be at a caravan's rear. See here as to why and here on further information on correct trailer loading.
Never add extra weight at the rear of a caravan to reduce tow ball mass. Instead, redistribute weight inside the trailer as centrally as possible until the correct tow ball mass is achieved.
A few caravan makers have (recently) relied on front-located water tanks to be full whilst towing to obtain that required mass! This is potentially so dangerous that most have been recalled and the tanks re-located. (Recently published photos of rolled-over caravans show that many have these so-located water tanks).
The recommended tow ball weight is only valid if the trailer is correctly loaded.
Tow Ball Weight - the right percentage
For a typical, medium-sized ( 6 to 7 metres long) Australian built caravan, tow ball weight should be about 10% of the trailer's laden weight.
For a generally lighter UK or European built caravan, tow ball weight should be around 6% to 7% of the trailer's laden weight.
For short camper trailers, tow ball weight can be as low as 5%.
In all cases follow the recommended tow ball weight of your trailer manufacturer, but first make sure that is within the maximum tow ball weight allowance of the tow ball/tow vehicle manufacturer.
Tow Ball Weight - how to measure it
A simple way to measure tow ball weight is via a length of timber placed under the trailer hitch and on top of a set of bathroom scales. Do not attempt to measure weight at other points on the A-frame (such as at the jockey wheel), since this will give a false reading. Raise the jockey wheel slowly as weight on the timber and bathroom scales increases, but keep the jockey wheel just clear of the ground in case the timber collapses. Note that most bathroom scales only measure up to 185 kg.
A better way is to buy a proper set of tow ball scales. They are not expensive (around A$75) and are safer to use due to their moulded tow ball shape at the top and solid base. They are thus more stable - and typically measure tow ball weights up to 350 kg.
Tow Ball Weight - when to measure it
When you first buy your caravan or trailer, measure its tow ball weight for a range of situations. This might be a light configuration (for weekends away), a medium configuration (for weeks away) and a heavy configuration (for months away). To see the effect on tow ball weight by moving items within the trailer Click here.
Also check tow ball weight with water tanks empty and full. See above re caravans with front-located water tanks. That (in RV Books' opinion) dangerously limits the required tow ball weight to being only when the water tanks are full.
Once you become familiar with the correct loading patterns for your caravan, continue to measure tow ball weight periodically to make sure no loads have been shifted and overlooked. Keep a set of tow ball scales handy and use them often, especially when you take on new or unusual loads such as bicycles or other new accessories. You may find others would truly welcome you measure their tow ball weight!
If/when discussing the above with anyone who knows physics, you will score Brownie Points by referring to tow ball weight as tow ball mass.
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