All-terrain versus mud-terrain tyres

The all-terrain versus mud-terrain question generates more argument than almost anything else in four-wheel driving, and the answer for most Australian touring is fairly clear once you look at where the kilometres actually go.

What the categories mean

All-terrain tyres are a compromise design: a moderately aggressive tread with reasonably tight blocks, siping for wet grip, and a compound that balances wear against traction. They work acceptably everywhere and excel nowhere.

Mud-terrain tyres use large, widely spaced blocks designed to bite into soft ground and, critically, to eject mud as the tyre rotates. Wide voids are the whole point: mud packed into a tread makes it a slick.

Highway terrain tyres are what most vehicles come with and are optimised for bitumen. Fine if that is where you drive.

Where the kilometres actually go

This is the argument that settles it for most people.

A typical touring trip is overwhelmingly bitumen and formed gravel. Even an ambitious trip spends the large majority of its distance on sealed roads getting to the interesting part. The genuinely difficult driving might be a few percent of the total.

Mud-terrains are worse than all-terrains at almost everything in that majority:

• Noise. Considerably louder at highway speed, and it is fatiguing over a long day.
• Wear. Softer compounds and big blocks wear much faster on bitumen.
• Wet grip. Fewer sipes and less contact area means longer wet braking distances. This is the safety argument and it is the one worth taking seriously.
• Fuel. Heavier, with more rolling resistance.

They are better in genuine mud, and better against sharp rock because of tougher sidewall construction.

So the question is not which is better. It is whether you spend enough time in mud to pay the daily cost of running them everywhere else.

For most people the honest answer is no.

Load rating matters more than tread

This is the part that gets less attention than it should, and in Australian conditions it matters more.

A loaded touring vehicle on corrugations is exactly the condition that kills tyres. Heat builds, sidewalls flex repeatedly, and an under-rated tyre fails.

Look at the load index on the sidewall and check the four tyres together comfortably exceed your vehicle's gross vehicle mass with margin. On a heavily built touring vehicle, that frequently means light truck construction rather than a passenger-rated tyre.

Light truck tyres have stiffer sidewalls and higher load ratings. They ride slightly harder and they tolerate load and heat far better.

This connects directly to weight discipline. If your vehicle is near its limits, the tyres need to reflect that. See GVM upgrades explained.

Reading the sidewall

A marking like 265/65R17 120/117S breaks down as:

• 265 — section width in millimetres
• 65 — aspect ratio, sidewall height as a percentage of width
• R — radial construction
• 17 — rim diameter in inches
• 120/117 — load index, single and dual wheel fitment
• S — speed rating

Also worth finding: LT for light truck construction, the ply rating or load range, and the 3PMSF symbol if alpine travel is on the cards.

Sand, which surprises people

Aggressive mud-terrain tread does not help in sand. It digs.

Sand driving is about flotation: a long contact patch spreading load across the surface. All-terrains generally do this better than mud-terrains.

More importantly, pressure matters far more than pattern. A modest all-terrain at correct sand pressures will comfortably outperform an aggressive mud-terrain at road pressures. See tyre pressures for sand, gravel and rock and beach driving.

Sharp rock

This is where mud-terrains have a genuine case beyond mud.

Much of remote Australia is gibber and sharp rock, and the failure mode is sidewall cuts rather than punctures through the tread. Mud-terrain construction is usually tougher in the sidewall, and some all-terrains offer reinforced versions for exactly this reason.

Counterintuitively, sharp rock is also where you keep pressures up rather than down. A soft tyre pinches its sidewall against the rim on rock and cuts.

Spares

Two spares is conventional advice for the remote unsealed routes, not cautious. The Gibb River Road and the outback tracks routinely destroy tyres, and it is sharp rock and corrugations doing it.

Carry a plug kit as well, because a repairable puncture should not consume a spare.

Match your spares to what is on the vehicle. A road-pattern spare on a set of light truck all-terrains is a compromise you will discover at the worst moment.

The practical recommendation

For most Australian touring: a quality all-terrain in light truck construction with a load rating comfortably above your loaded weight. That combination handles gravel, sand, rock and the occasional mud, and does not punish you for the thousands of highway kilometres in between.

Choose mud-terrains if you genuinely spend significant time in mud or on sharp rock, and accept the noise, wear and wet-weather trade knowingly rather than by accident.