If you own a motorhome, you probably know that many motorhomes sold in New Zealand have a Gross Vehicle Mass (GVM) of 3,500 kg or less to meet WOF requirements. However, with tare weights often around 3,200–3,300 kg, you don’t have much payload left—sometimes as little as 200 kg. When you add another occupant, food, drink, and clothing, you can quickly overload the vehicle. Even if you stay within the GVM, exceeding the weight limit on a single axle remains dangerous because you push the axle, suspension, rims, or tyres beyond their design limits. If you drive overloaded and crash, your insurance provider could reject your claim.
Even motorhomes with a GVM over 4000 kg can be exceeding their maximum allowable vehicle weight or maximum axle weights.
Overseas research shows that about half of all motorhomes run overloaded, and New Zealand likely sees worse results. Driving overweight directly affects safety and comfort, and it can also earn you an expensive police fine. In most cases, owners overload their vehicles because they don’t know the true load capacity. Many pack their vehicles without realising the consequences.
When you re-rate your vehicle, you make it safer at higher loads because we fit additional suspension components to support the extra weight.
Take my own motorhome as an example. I own a 7.5 m Fiat Ducato with a large rear overhang. On the brake rollers at VTNZ during a COF inspection, the rear axle has weighed in at 2,000 kg—the maximum allowed.
Now imagine what happens after I add water, fill the fridge, load people, carry bikes, and store gear in the garage. Although I weighed just under the GVM of 3850 kg, the rear axle was 170 kg over loaded, which exceeded both tyre and rim ratings. Not good.
I have since upgraded my Fiat Ducato, which has the “light” chassis. Its GVM now sits at 4,000 kg, and the rear axle rating increased from 2,000 to 2,240 kg after I fitted an approved supplementary air-assisted suspension kit to the existing mechanical suspension from VB Air Suspension.
With the VB Airbags fitted, I gained two major benefits: a higher loading allowance on the rear axle and better handling and ride comfort across the entire weight range—from unladen to fully laden. The driver controls included in the Comfort Kit also let me partially raise or lower the rear suspension, which makes loading easier and helps with leveling.
Below is the increase in ground clearance at the rear of my 7.5m Fiat Ducato based motorhome with leaf springs can achieve by varying the pressure in the airbags.
| Pressure (Bar) | Increase (mm) |
|---|---|
| 0.5 | +10 |
| 1 | +20 |
| 2 | +30 |
| 3 | +40 |
Note: exceeding 3.5 bar air pressure is only for slow speed maneuvering below 5km/hr. Note: Comfort kits have a pressure relief valve set to 3.5bar on the compressor.
If you have a motorhome based on the Fiat Ducato, Citroen Jumper / Relay or Peugeot Boxer with only a small gap (15mm or smaller) between the rear axle and suspension bump stop like below (ie between the red buffer and the top of the leaf spring), then its quite possible that you too are exceeding the rear axle weight limit of your vehicle.
A technical report written by Fred Hollows, the NZTA adviser to the New Zealand Motor Caravan Association, can be found here further discussing the problem with GVM’s of 3500 kg.
Motorhome Tyre Pressures
Here is a link to a UK website with a calculator for suggested motorhome tyre pressures. https://www.tyresafe.org/check-your-pressures/motorhomes/
Also see their technical information guide on tyres https://loadsafe.nz/wp-content/uploads/2020/08/motorhome-tyre-pressures.pdf
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