I like to think that a lot of people are now aware of the requirement to be under the GVM, or Gross Vehicle Mass. As such, I’m moving onto talking about other items that people might not understand as well, like Tow ball weight, and the leverage that goes with it.
Perhaps the best demonstration of tow ball weight is when you take a really heavy trailer, and you attach it to a car that has soft springs.
What happens? The rear of the vehicle sags (goes down), and sometimes to the point where the suspension is bottomed out. However, if you look closely, whilst the rear of the vehicle goes down, the front of the suspension goes up!
This is simple leverage, and occurs when you apply weight to the tow bar, which is a decent distance from the rear axles. The leverage causes weight to come off the front of the vehicle, and move to the rear.
For example, if you have a 300 Series Land Cruiser, and you hook a trailer onto the tow ball with a 350kg tow ball weight, how much weight do you think gets applied to the rear axles?
If you said 350kg, you’d be incorrect, as its actually more due to some weight coming off the front, and moving backwards.
There is an equation that you can use to work out the leverage, and how much weight is moved off the front of the vehicle to the rear, which involves the wheelbase length, distance from the tow ball to the centre of the rear axle and the weight itself.
For many dual cab Utes though, you end up applying about 1.5 times the weight to the rear axle. If you take a 300kg tow ball weight, you are going to end up with nearly 450kg of weight on the rear axle from the tow ball weight alone, simply because its taking 150kg off the front of the vehicle and moving it to the back.
Now, the exact result that you get may vary a little depending on how your suspension is set up, what heights the hitches run at and so forth, but at the end of the day you can’t avoid the leverage.
High tow ball weights can be very risky
With this in mind, its important that you understand that having a high tow ball weight can be very risky for a number of reasons. Firstly, from a mechanical perspective, having an extra 450kg applied to the rear axle of your dual cab Ute makes it want to bend, and that’s exactly what has happened to thousands of vehicles across Australia.
You don’t need too much weight and a small dip in a 4WD track, or along the beach and suddenly your dual cab ute chassis looks more like a banana. We’ve seen this happen, and you can read more about it at Bent Dual Cab Chassis.
The flip side of the coin though, is that your vehicle has a maximum rear axle capacity which you must also meet, along with your GVM, GCM and a myriad of other requirements.
It is entirely possible to be under GVM, but over your rear axle weight due to a heavy tow ball weight, and that puts you in the same position; driving an unroadworthy 4WD that your insurance company can reduce or decline any claims on!
Hopefully the learnings from this are simple; if you don’t know your tow ball weight, go and get it checked. If you don’t know your rear axle weight, get that checked too, when you are loaded up.
If you have a tow ball weight that is excessive (either because its higher than it should be, or because its higher than what your vehicle should take), then you might need to make some difficult decisions.
Our Reconn R2 has a tow ball weight around the 130 – 150kg mark, and I specifically hunted for something with a light tow ball weight because I like my Dmax in one straight piece.
Some hybrids and caravans are applying ridiculous amounts of pressure to dual cab Utes, and the likelihood of something going majorly wrong when you are remote and away from everyone and everything is simply too high.
What’s your tow ball weight, and leverage like?