LOCK & LOAD
By Grant Spolander
Does your 4x4 have aftermarket suspension? If you’re an off-road enthusiast, there’s a good chance that it does. Why? Because most of us have accepted the fact that aftermarket suspension does a better job at carrying heavy loads.
But what about your tyres? Are they designed for heavy loads? Or should they be upgraded, too?
Depending on the load, it’s recommended that 10 to 50% more air be added to your tyres when your vehicle is heavily loaded. Most of us have accepted this notion when travelling on holiday, or for long distances, but we tend to ignore this fact on shorter journeys. There, the common consensus is: “Ag, man, it’s just down the road; I’ll drive slowly and the tyres will be fine.”
The fact is that structural (permanent) damage can happen in an instant, and although it may not manifest itself straight away, the damage to the tyre could come back to haunt you many miles (or months) down the road when the tyre suddenly fails.
However, there’s an even greater tyre problem that no-one EVER talks about: Load Index!
When was the last time you heard two blokes arguing about Load Index? Almost never, right? You’ve probably heard many debates about mileage, traction, or which tyre won the latest magazine tyre-shootout, but no-one ever talks about Load Index. And it’s bizarre, because it’s a factual way to gauge tyre strength.
What I find even more surprising is hearing someone advocate the fitment of an OE all-terrain to a heavily-laden vehicle. Here’s the thing about OE fitted all-terrains: just about all of them have a mediocre Load Index.
Have a look at your OE tyre’s sidewall and see what the Load Index is. I bet it’s somewhere around 950 to 1 100kg per tyre, which, in most cases, is not much higher (if at all) than a Passenger tyre, or even an OE-fitted highway terrain, for that matter.
Another point to remember about OE tyres is that they’re sourced (by the vehicle manufacture) for the following qualities:
- They must be cheap
- They must be lightweight (which means better fuel economy) and
- They must be flexible (for better comfort).
This is because most vehicle manufacturers are doing their best to minimise costs while maintaining competitiveness in the fuel economy and comfort departments.
No vehicle manufacturer in their right mind would launch a brand new double-cab with costly, heavyweight tyres that use more fuel, and ride harder than their competitors. Just about every motoring journalist in SA would criticise the vehicle as too “utilitarian, uncomfortable, and heavy on fuel”.
Of course, very few of them would recognise that the tyres were playing a crucial role in the vehicle’s performance, or that they were also ignoring the benefits gained from using a tougher tyre with a high Load Index.
But what is a high Load Index, and how do you measure one tyre against another?
The simple answer? You shop around.
Heavy-duty Light Truck (LT) tyres offer a higher Load Index than light-duty alternatives. That said, dedicated off-road tyre brands will offer a wider range of Light Truck products and sizes.
It’s important to note that the Load Index is not fixed for certain tyre models. The Index will depend on the size of tyre you opt for. For example, when I shopped around for a set of tyres for my Patrol, I had my heart set on Cooper STT PROs − so that part of the decision was already made. The difficult part was deciding which tyre-size and subsequent Load Index I wanted.
If you look at the table attached, you’ll see that the STT PRO’s Load Index varies from 1 216 to 1 751kg, depending on the size you opt for. This is true for most tyre manufacturers, but (as mentioned before), dedicated off-road tyre brands generally offer a much wider range of tyres with a high Load Index.
Again, OE fitted tyres will offer a Load Index in the region of 950 to 1 100kg.
I eventually fitted 285/75/R16s to the Patrol, as these tyres have a Load Index of 1 701kg per tyre. That’s roughly 55% more strength than an OE tyre.
But why is that important? If four OE tyres can handle 4 400kg in total, isn’t that more than enough? The Gross Vehicle Mass of a typical double-cab is in the region of 3 000kg...
That may be true in a numbers game, but in a world where many of us fit bull-bars, winches, canopies, long-range tanks and a ton of camping gear, do you really want to push the limits of your tyres in a remote, off-road environment that has a high concentration of hazards and obstacles?
We’re not talking about the N1 here. Tyre failure is far more likely to happen on a steep, rocky track when your vehicle’s weight is predominately on the front tyres and you’re forced to make static steering inputs over sharp rocks.
Ultimately, the choice is yours; but the subject of Load Index should be a vital consideration for any 4x4 enthusiast that has mulitple accessories fitted to his vehicle.
Sure, the benefits of aftermarket suspension have been proved in the 4x4 arena, but at the end of it all, where’s all that weight finally resting?
On your tyres.