In this article, David from Dwn Under Caravan Weighing and Repairs gives us an expert’s view on tow vehicles and questions to keep in mind before a big purchase. Read on and let us know your thoughts in the comments.
When looking at purchasing a tow vehicle, or if you already have one, it’s important to consider the tare weight, payload, GVM, GCM and how much it can tow, safely and legally.These fundamental questions could get you out of future trouble by asking them before you purchase your tow vehicle. So, let’s start at the very beginning and try paint a picture for you to follow.I will be using the Isuzu D-MAX as an example to showcase the weights and considerations.Tare Weight / Unladen WeightThis is the weight of your vehicle when it is empty and completely standard, with no passengers, no luggage, no aftermarket accessories and no other gear. This does include 10L of fuel and all fluids at maximum capacity (oils, coolants, fluids etc).
For example, the Isuzu D-MAX tare weight is 2020kg. This weight can’t change, you can’t add to it or take away from it, it is the weight of the stock vehicle as built by the manufacturer. It’s important to know your tare weight so you can get maximum payload.
You might be thinking, “Why is payload important?”
Keep going and you’ll find out, but next, let’s talk about your GVM.
Gross Vehicle Mass (GVM)Gross Vehicle Mass (GVM) is the safe and legal limit that your vehicle is allowed to weigh when it’s fully loaded with everything, like a bull bar, roof racks, all your luggage, a full tank of fuel and all of your campsite goodies to enjoy by the fire.
Where a lot of people get caught out is when they forget to add their Tow Ball Weight (TBW). Once you have hitched your trailer/caravan to your tow vehicle, you are adding tow ball weight that will count towards your GVM as it is weight that the vehicle is carrying. CLICK HERE to read more about tow ball weights.
The good news is that you can upgrade your GVM. GVM upgrades focus predominantly on suspension, with firmer spring rates and shock absorbers able to better handle additional weight and air bags sometimes added to allow rear spring rates to be varied to suit the weight carried. Brake and other safety upgrades can be part of a GVM upgrade too. An increase in GVM will also increase your payload but it’s not always as simple as fitting the parts, with engineering often required to legally upgrade GVM.
Despite what some may tell you, GVM upgrades aren’t always an ‘upgrade’ and are best suited to vehicles that are a lot heavier than their factory tare weight on a regular basis. Stiffer GVM-upgraded suspension will sacrifice ride comfort and performance when carrying less than the load it has been designed for, so it’s worth having a clear idea of the minimum and maximum weight your vehicle will be to compare that to GVM before deciding what suspension is right for you. CLICK HERE to read more about aftermarket 4X4 suspension.
PayloadFinally, payload. This is the total weight you are allowed to add legally and safely to the vehicle within its GVM, less its tare weight. It includes your aftermarket accessories, (bull bars, roof racks, bigger tyres and rims, etc.), luggage, passengers (yourself included), a full tank of fuel, and your Tow Ball Wass (TBW) once hitched up.
To get your payload, it’s pretty simple math, just take your tare weight off the GVM, and you are left with your payload. As an example, the Isuzu D-MAX’s GVM is 3100kg, you then subtract the tare weight, which is 2020kg, and that equals a Payload of 1080kg! That’s a nice amount of upgrades you can attach before you hit your limit.
While this back-of-the-napkin math will give you a good idea of what weight you can legally add to your vehicle, it’s still a great idea to have it weighed. If you can measure axle weights too to get an idea of how your weight is distributed (or how it could be distributed more evenly), this can also influence things like vehicle stability and the tyre pressure required to carry this load.
If you’re in Victoria, the Dwn Under team would be happy to help you weigh your vehicle. If not, you can often find a public weighbridge in your local industrial area or near a rubbish tip, just make sure to ask that they weigh each axle separately, which often doesn’t cost any extra and simply involves parking the vehicle over two weighing pads.
This article focuses on 4X4s as tow vehicles, but you can learn more about GCM and other weight considerations for trailers in the article below.
The Towing question no-one wants to answer
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