Tow Ball Weights
Weighbridge vs Calibrated Tow Ball Scale Experiment.
Caravan tow ball weights are a very sensitive subject, literally! The difference when measuring caravan tow ball weights off a calibrated tow ball scale compared to a weigh bridge is astounding!
Why do we need to worry about tow ball weights? When looking at tow ball weights we talk about them being too light, too heavy or in the ballpark (due to forever fluctuating weights), but what does that mean? When talking about the ideal tow ball weight we want to aim for 10% of the caravans ATM (Aggregate Trailer Mass). So, if your caravan weighs 3000kg, the ideal tow ball weight would be 300kgs. At AusWide Weighing we allow for 1% either side of this, so are happy with a tow ball weight between 9% and 11% and take any figure between these ranges as in the ballpark. If a tow ball is light, you have the potential to start swaying side to side at a lower speed, become unsteady and potentially jack knife. If your tow ball is heavy, you are potentially placing unnecessary strain on to your vehicles tow hitch and transferring extra weight to your rear axle. This extra weight can be up to 160% of the actual tow ball weight. Any extra weight transferred to your rear axle will take weight off the front axle and unfortunately this comes with its own issues (Think of it like a playground seesaw… now, add 300kg to your tow ball at 160%, this will add 480kg to your rear axle and remove 60% or 180kg off the front axle ). A vehicle with a heavy rear and a light front can negatively impact the steering making it feel too light and potentially unsafe as well as causing poor traction which can make breaking unsafe and not as effective as having a balanced vehicle. Once hitched to a trailer or caravan we assume that any sway felt whilst driving must be coming from the trailer or caravan when in fact, it could be the car itself. So, with that being said, it is very important to get the correct and ‘actual’ weight of the tow ball when doing your weights.
At AusWide Weighing we use a specific tow ball weigher that weighs to the kilogram. To ensure the most accurate measure we weigh the tow ball at the same height that the caravan or trailer is towed at when hitched to the tow vehicle. We know, that increasing or decreasing the tow ball height will either add or subtract weight depending on whether you are towing a single axle or dual axle caravan or trailer. We have seen these differences of up to 10kg per 25mm, this is a considerable amount, especially on caravans with an already too heavy or too light tow ball weight.
For example (dual axle): if your tow ball is 300kg at 400mm, and you raise your tow ball height to 450mm, it has the potential to raise your tow ball weight to 320kg. Inversely, measure the tow ball at 350mm the result will be around 280kg.
Scenario – Our client had concerns about his tow ball weight. He had taken it over a weigh bridge, where the tow ball amount measured was at the jockey wheel and at the height he had raised it to be able to unhitch from his vehicle, his tow ball reading was 320kg, putting him over his legal limit of 300kg. The result when weighed at the correct hitch height whilst using our calibrated tow ball scale was 250kg. To summarise, our client went from being over their legal limit to being well under and in fact having room to add more to the tow ball weight to be at the perfect TB weight of around 10% of actual ATM.
When measuring tow ball weights on a weigh bridge the readings are generally taken from the jockey wheel and at what ever height you have the jockey wheel raised to. As mentioned above, the height your tow ball is measured at will impact the reading you get and likewise, where your jockey wheel is in comparison to your tow hitch can vary and change the “tow ball’’ reading dramatically.
Example 1: We measured the client’s tow ball weight at the tow hitch height of 590mm, we then measured the weight at the jockey wheel which was situated around 500mm back from the tow hitch. The difference in the results was upwards of 70kg. Therefore, we increased the tow ball weight reading by weighing the tow ball at the jockey wheel instead of where the hitch is.
Example 2: We weighed a 2021, 22’6’’ dual axle family caravan. The height of the hitch when towing was 500mm, at this height the tow ball mass (TBM) was 347kg. We repositioned the tow ball scale to the jockey wheel, which was located around 700mm away from the tow hitch, we recorded the mass at the same height of 500mm which was 399kg. The final result was at the jockey wheel the TBM was 52kg heavier than at the tow hitch.
Weigh bridges are easily accessible and can be a great guide, but unfortunately do not give cars and caravans all the correct weights needed to consider when towing. Weigh bridges are mostly set up to be used by trucks, and most measure in 20 to 25kg increments meaning the weights you receive when going over a weigh bridge can have great variables and therefore are not the best when gauging caravan/trailer tow ball weights. We use brand new, state of the art and calibrated (annually, by NATA certified companies) weighing equipment that measures down to the kilogram to give you the most accurate reading possible.
Get your weights, know your weights and understand your weights properly by booking an appointment with a mobile weighing company using the correct equipment!
