When it comes to upgrading your vehicle to tackle Australia’s wild and varying off-road terrains, a set of aftermarket tyres like Toyo Tires’ legendary Open Country range is but one of a myriad of modifications that enthusiasts choose to make, and is often accompanied by improving the vehicle’s capability in the bush through bullbars, rocksliders and vehicle armour, or the addition of bespoke items like rooftop canopies or tents, custom-made trays for utes or the addition of a tow-behind trailer or caravan.
There’s no denying that all of these additional features provide increased off-road capability, as well as added creature comforts or safety when off the beaten track, but how often do we think about how all these features affect the weight of our vehicle, and in turn, the effect that vehicle weight can have on our choice of tyres.
To start with, we need to know our vehicle’s Kerb Weight. This can be easily found online or in your Owner’s Manual. Your Kerb Weight is the way your vehicle came from the factory, before you started accessorising it to head bush. From here, we need to calculate the weight of the accessories you’ve added, and see how this new number (vehicle Kerb Weight + accessories) compares to your vehicle’s Gross Vehicle Mass (GVM).
Your GVM is the maximum legal operational weight for your vehicle, fully laden - the weight of any accessories you’ve added, as well as the weight of anything you’ve got contained in the vehicle including passengers and cargo which Steve Burke, Tyre Technical Manager from Toyo Tires Australia points out, can have a huge impact.
“If you think being 500kg away from your GVM gives you plenty of head room then consider the weight of four passengers and their cargo for a weekend camping - it adds up quickly, and it’s not difficult to exceed your GVM,” explains Steve.
The good news is that a set of quality tyres can usually handle a vehicle exceeding it’s GVM marginally, however the correct tyre pressures are key.
Steve points out that calculating the correct tyre pressure for any vehicle that’s been substantially modified all starts with a trip to the local weighbridge. “If you’re based in any metro area around the country, just Google your local weighbridge. For remote or country areas, the local tip will often have a weighbridge,” he explains.
For best results, Steve encourages drivers to get individual axle weights as well as an overall weight, to help identify if either end of the vehicle is working harder than the other. “Take some mining vehicles for example, which equip their 4x4 worksite vehicles with big tool boxes, or require the vehicles to carry heavy machinery buckets or the like. This gives them a huge weight bias to the rear, in turn impacting vehicle handling, which you’d certainly notice on unsealed roads,” clarifies Steve.
For your average offroader though, it’s a matter of taking these axle weights and recommending tyre pressures based on the terrain you’ll be covering, rather than relying on a ‘one size fits all’ approach.
But why are axle weights and pressures so important? As Steve explains, using vehicle mass to calculate the ideal tyre pressures will go a long way to optimising tyre life, as well as performance and safety.
“Aside from the sacrifices in ride quality, there can be a safety impact as well,” he says succinctly. “We need to remember that vehicles are dynamic and loads shift, so we’ve got to factor that in to our calculations when recommending pressures, and we need to build a margin of tolerance in to our calculations because we’d never recommend anyone exceeding, say, 95% of a tyre’s load capabilities.”
“Weight-related tyre failures are far more common than people think, especially while a vehicle is moving, and in-service tyre failures are the one thing we try and avoid because of the safety issues attached,” says Steve in closing.
If you’re looking for tailored tyre pressure advice for your Toyo Tires-equipped vehicle then you can contact Toyo Tires Australia directly, or consult with your local Toyo Tires Dealer.
Steve’s Top Three Tips:
- Consider your tow ball weight - whether you’re towing a box trailer or a large dual axle caravan, this Tow Ball Download affects your GVM and puts extra stress on your rear tyres, so if you’re looking for tyre pressure advice let your tyre specialist know that you’ll be towing
- Think about where your weight is - if you think of your axles like levers, then loading your vehicle can become a game of physics. Vehicles that are top-heavy (like single cab utes that carry slide-on camper vans) don’t just have weight over the rear axle, they also have the added stress of additional loading to the side wall of the tyre when the top the vehicle corners
- If in doubt, go up - depending on your set up, you might find that your new vehicle mass means that you’ve outgrown your OE tyre recommendation. This might mean moving to a larger width or diameter tyre, moving from Passenger Construction to Light Truck or even re-engineering your vehicle with a GVM Upgrade to suit your modifications
