Slide On: GVM Explained
Now I’m not a four wheel drive enthusiasts where four wheel driving is more of a sport. To me. it’s just a means to an end. To have the ability to explore beyond the bitumen.
But just like you need to know what pressure you put in your tyres, you need to know the basics of what load you can place on your vehicle. Here’s the basics of what you need to know….
• TARE WEIGHT: The weight of an empty vehicle including all fluids but only 10 litres of fuel in the tank.
• KERB WEIGHT: The Tare weight but with a full tank of fuel, not including payload.
• GVM: (gross vehicle mass). This is the legally allowed total loaded weight of the vehicle (Kerb Weight plus Payload). For your typical four wheel drive, round figures is about 3,000kg
• PAYLOAD: – the difference between the GVM and the Kerb weight. Effectively the total load you add to the vehicle.
• GCM: (Gross combination mass) – the maximum total weight for both vehicle and trailer.
If your eyes have started to glaze over, I understand. The one critical thing you need to know is what your manufacturer’s stated GVM is. Often this is plated on the inside of one of the front doors. Then the simplest way to check your spare payload capacity is find a local weighbridge or go down to your local tip, drive onto the weigh bridge and ask them for your weight.
If you do this with your vehicle before you load the back up, you will then have an accurate idea of what load remains to load on the back. Then, add in the dry weight of your camper to then calculate what extra you have left to load in, such as water, food, drinks, accessories, extra passengers, etc. It's also a good idea to recheck your load after you are fully loaded and about to head off. It's nice to know you are within legal limits.
Why do you need to ensure you don’t go over the GVM limit? If you are loaded up and the vehicle looks level, what’s the problem you may ask? Or maybe you had an extra leaf put in your springs or airbags fitted to straighten up the vehicle. All looks good so why bother if the weight is over. One simple reason…. insurance. Like most things in life, everything is fine until something goes wrong. Like an accident. As we all know insurance companies only need the slightest excuse to avoid their payout obligations. There’s also the legal implications where the law may not look at you favourably if you are the cause or involved in an accident.
If you want to make sure you stay legal, there’s usually no alternative but to do a GVM upgrade. Sure, if you practice minimalistic living or camping in this case, you could probably expect to be within standard GVM limits. But if you are heading off into the outback and need to be self sufficient, the need to carry extra water and fuel, a couple spare tyres, and some essential tools, this will all undoubtedly set you over your GVM limit.
That’s why slide on camper and GVM upgrade almost go together. If you are purchasing a new vehicle, having the GVM upgrade done prior to registration will save you the extra compliance if you do it later. Generally, the upgrade costs about $3,000 to $5,000 and will give you an extra 300Kg of payload.
The upgrade comprises of a package that includes shock absorbers, springs and other suspension components, plus an assessment of braking and stability testing to ensure the vehicle’s safety standards are capable of carrying a greater payload.
If you are considering airbags, it would be wise to obtain professional advice. Normally the load on the rear axle is distributed across each end of the leaf springs. Air bags are mounted directly between the axle and the chassis. Too much pressure in the airbags effectively changes the weight loading of the chassis to directly over the axles. That results in lesser weight bearing at each end of the leaf spring mounts, thereby changing the manufacturers load design. A number of people claim airbags are attributed to bent chassis. Others disagree. So, once again seek unbiased expert professional advice if you choose airbags and also how you use them, such as never having the pressure of airbags greater than your tyre pressure.
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