David Wilson is a 4WD driver trainer, one of the best in the country, running his business Adventure 4WD in Adelaide for over 25 years. He’s also the face of Isuzu’s I-Venture Club, teaching droves of D-MAX and MU-X owners during the four years IVC has rolled around the country. He’s also the co-publisher and technical writer for Loaded 4X4 Magazine – The Cult of Off-Road.
I won’t be the only one shivering my arse off at the moment since we are now well and truly into winter in the Southern States. In my part of the world, not only is it cold, but we’ve also had that wet stuff falling out of the sky, so tracks around here are positively damp.
Now I’m a bit of a tyre-tragic. I love the science behind what makes a good tyre and I know how to extract the best life out of them. After all, a 4WD tyre is a pretty expensive thing when the time comes around to get a new set and maximising the mileage travelled is critical to my fleet operation costs.
I also like to make sure that I match my tyres to the experience I’m going to dish up to them, so I’ve got a summer set; Toyo Open Country A/T IIs (all-terrains) in LT265/70R17 121S, and a winter set; Toyo Open Country M/Ts (mud-terrains) in LT265/75R16 123R. Now in case you’re thinking what I’m about to say is influenced by Toyo because they gave me each set, sorry, not so; I paid good money for these, as I like to be able to comment and retain impartiality. That is something very rare in 4WD media circles these days.
Now I’m not usually a huge fan of muddies because they come with some compromises as they are a very specific tread pattern for a very specific environment. But in some parts of this country of ours, they are very, very useful. If I lived in the Alpine regions or in places where watercourses were a regular part of my daily drive, they’d be up there amongst my first choice.
In my home town of Adelaide, we seldom get rain, but my property used for our driver training does get wet and holds that surface water for months. Coupled to frequent trips we do into the Flinders Ranges, the justification for the use of muddies is real, so they get a guernsey in winter.
The size I selected too was a deliberate ploy because my benchmark for consistent performance and bulletproof strength is measured in Load Index. You’ll read what I had to say about Load Index and the need to achieve a minimum 120 Load Index in a previous Toyo Blog I wrote HERE and I call it the 120 Rule. So I know right from the get-go these are SERIOUSLY tough tyres and my expectation is a minimum 80,000kms life before I bin them, based on my past experience.
Now you might ask: “80,000kms but in what condition at the end?”
I’ll be expecting a tread face/tread blocks that’s evenly worn down to around 3-4mm depth (I’m not a believer in wearing right down to the TWI - tread wear indicator) with no chipping or tearing and no history of puncture.
How is that possible? Simply by managing them correctly!
The first part of the puzzle is pressure. I see it all the time in the classroom and when I’m out in the field, vehicles suffered/suffering repeated tyre failure and damage due to over-inflation. There’s a really handy piece of starting information that vehicle makers supply with each 4WD and it’s called a tyre placard.
On my D-MAX, the pressures are 200kPa front and rear when lightly laden, say a full tank of fuel, a single passenger and a modest cargo. When operating at GVM, the backs get a boost to 280kPa. In imperial-speak, that’s 30psi front and rear unladen, the backs going up to 40psi when heavy.
That’s your starting point on the bitumen. Then on the dirt, we get more involved.
High speed dirt (and that’s up to 80km/h because any faster will likely catch you out one day and it’ll hurt) deserves a 20% reduction from those previous pressures, and that’s something I call my 20% Rule that you can read about HERE. This pressure reduction increases tyre flexibility, allowing the tyre to softly absorb impacts while conforming to the surface you’re travelling across rather than remaining rigid and risking a rupture or accelerating wear. The tyre (and the rest of your vehicle) can only safely absorb so much though, with even small reductions in speed greatly reducing impact forces.
Anyway, as track conditions deteriorate further, you keep letting air out and slowing down. My time in the Flinders Ranges scrambling up and down really nasty quartzite hills and shale lining the creek beds is done typically between 125-140kPa or 18-20psi and those pressures are A-OK for speeds up to 60km/h until the cows come home! Keep your speeds low whilst at low pressure and no damage will be done.
Naturally, when the high-speed run home on the bitumen happens, we need to pump back up to placarded pressures again. That will regulate the temperature in the tyre nicely and prevent a heat-related failure while increasing your safety margin for extreme weight transfer in an emergency situation.
Do all of this and your experience will be the same as mine; sure-footed handling in the mud, gravel and bitumen, nice short stops in emergencies, excellent durability and longevity with the promise of 80,000 kilometres at least and NO DEGRADATION!
If you’re in the habit of chewing up the face of your tyre, you’re clearly managing them really poorly and setting yourself up for a fail, or you bought the wrong brand. Tyres aren’t magic, if you beat them up, they’ll start to show it eventually, so take care of them and they’ll take care of you.