Check your tow ball weight with empty water tanks

When it comes to towing, ensuring you have a suitable tow ball weight is one of the most important factors to get right. If you aren’t familiar with it, this is the amount of weight that your trailer applies onto the tow ball (or DO35, Mchitch, Treg hitch etc). 

For those of you who are familiar with it, you’d know that it changes a lot as you travel, depending on how you are loaded up, where you put things and often how full your water tanks are. Some caravans install one tank on one side of the axle, and one on the other, meaning that the weight should stay roughly the same all the way through the water consumption exercise, but there are many that do not.

Tow ball weight of our Reconn R2
Checking our tow ball weight with empty water tanks

Our Reconn R2 Hybrid Camper for example, has three water tanks, with one of them being over the top of the axle, and the other two being behind. They aren’t that far behind, but I’ve always had this little worry in the back of my mind that as the water tanks empty the weight on our tow ball would skyrocket, and that’s not a good thing.

Water tanks in the Reconn R2
We have three water tanks inside our Reconn R2

Why does a heavy tow ball weight matter?

In terms of stability, having a heavier tow ball weight (providing your load is down low and near the axles) is good. However, to stick within your vehicles axle weights, and GVM having a heavy tow ball weight is really, really bad.

On many vehicles, your tow ball weight applies roughly 50% more weight to the rear axle, than the weight itself. For example, if you had a 200kg tow ball weight, you’d be applying around 300kg of weight to the rear axle of the vehicle. It does this through leverage; it removes 100kg off the front axle, and shifts it onto the rear, which is why your vehicle sags when you add a heavy tow ball weight.

Towing our Reconn R2
Tow ball weight can apply about 50% extra to the rear axle

For us, having a tow ball weight that changed hugely would make us illegal, as we are at the limits for rear axle weight, and also for GVM on our Isuzu Dmax.

Beyond this though, applying a lot of weight to the back of a dual cab 4WD is a recipe for a bent chassis, and that’s the last thing we, and you want. There’s literally hundreds of dual cab 4WD’s every year that end up with snapped or bent chassis, and the major contributing factor is heavy tow ball weights.

Dmax fuel use
I like my chassis straight, and lots of tow ball weight is never a good thing on a dual cab ute

Why should you weigh your trailer with empty water tanks?

At this point, you might be wondering why you’d bother weighing your trailer with empty water tanks. Surely you always have full water tanks when travelling? Well yep, you probably should, but what happens when you’ve been camped for a number of days and your water tanks are nearly empty? You still need to drive that setup back to town to get more water, and if its illegal, or unsafe that’s not a good place to be in.

Weighing our tow ball weight with low water tanks

So, when an opportunity presented itself to weigh our tow ball weight with the water tanks empty, I jumped on it. We’d been exploring the Yorke Peninsula for about 2 weeks, and we were running really low on water. Our Topargee water gauges were showing 39 and 24L left, and I’m not sure all of that is usable.

Topargee water tanks
Our topargee water tank flow meters were starting to get really low

To be fair, that probably equates to 93 litres of water left, if you drained every last bit out, and they were perfectly full. Neither is likely, so we’ll assume they probably had about 60L of usable water left (down from 270L when all 3 tanks are full).

Regardless of this, I threw Dad’s tow ball scales under the first part of the drawbar (it’s risky doing it under the DO35 hitch with it being able to twist), and was quite shocked to see the weight come in at 160kg, and then 170kg when I bounced it up and down and let it settle again.

When we left Perth, the weighbridge showed the tow ball weight at 160-180kg, and we were over our axle and GVM ratings, so I moved a fair bit of gear backwards. I never weighed the tow ball weight after this, but knew that it would have decreased enough to make us compliant.

I’m relieved, and very happy, as it means that in a worst case scenario, our tow ball weight is not going to be over the 180 – 190kg mark, which in my mind is quite acceptable, and we’ve never had any swag issues, which is perfect.

How does your tow ball weight change with empty water tanks?

I suppose I should give some credit to a post that I saw on the Reconn Facebook Group, where a member with a Reconn R4T was saying his weight was coming in at 370kg for his setup, with empty water tanks. Not only is that obscenely heavy, but its also illegal for any normal 4WD (as they have 350kg tow ball weight limitations), and that’s without looking at rear axle or GVM weights.

One of the reasons we ruled the Lifestyle Breakaway out when we were hunting for a camper was that they were 180kg on the tow ball with nothing in them, and it would only get worse as almost all of the storage was in front of the axles, with the water tank behind them!

Some hybrid and forward fold camper trailers have insane tow ball weights (like 250kg +) and in our mind, that makes them completely unsuitable for real 4WD work unless you have a ridiculously strong tow vehicle.

So, have you weighed your Caravan, Camper Trailer or Hybrid with full, and empty water tanks to see what the tow ball weight comes in at? If you did, were you shocked?

Water inlets on a caravan
Before you fill your water tanks, check the tow ball weight

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