Matching 4WD tyres with road conditions

04 Jan, 2017 02:29 PM

THERE are three main tread patterns fitted to Australian 4WDs: Highway Terrain (H/T), All Terrain (A/T) and Mud Terrain (M/T).

Each offers a different driving solution and experience so before choosing 4WD tyres you need to ask yourself a few questions.

Where do you go? What do you do there? How much time do you spend on sealed bitumen? How much is spent tackling off-road terrain?

The industry standard gives a reasonable guide.

H/Ts are for 90 per cent highway and 10pc off-road; A/T are for 60pc highway and 40pc off-road and M/T are for 15pc highway, 85pc off-road.

Toyo Tires technical manager Steve Burke said many H/T owners stray into A/T or M/T territory, only to spend their afternoon wandering the bush, searching for reception to call for a tow.

"It comes down to what you're going to do," he said.

"Ten per cent off-road, for example, doesn't mean you can point your car into any terrain you like.

"Aussie tracks are renowned for sharp surprises and radical changes.

"A highway tyre may get you through some off-road situations but you need to be mindful of the capabilities of the tyres on your car."

H/T tyres are fitted as standard on most 4WDs.

With small gaps between tread blocks, H/Ts boast greater on-road grip, offering more contact with the bitumen and reduced block flexing.

Their light construction makes them better suited to high speeds.

Smaller block gaps reduce heat build-up and prevent blocks from squirming under load.

Made primarily for on-road use, H/Ts are less suited to extreme terrain than A/Ts and M/Ts.

"H/Ts are street performers," Mr Burke said using Toyo's Open Country H/Ts as an example.

"They are extremely low noise and offer ride comfort matched with fuel efficiency and a long tread life.

"I wouldn't take them through the Tanami, but for the commuter who might use their vehicle on sand and for mild off-roading, they will do the job."

A/Ts are the middle ground between on-road and off-road performance - all rounders.

They're ideal for the commuter who hits the beach or the bush on weekends.

Larger voids between the five rib tread blocks eject debris and provide good on and off-road performance.

"A/Ts are often seen as a compromise with limited performance in certain terrains or poor traction in some street conditions, but that wisdom is limited," Mr Burke said.

A proper A/T performs in every situation, he said.

"Toyo's Open Country A/T II (OPAT II) has reduced road noise to levels similar to highway tyres, providing class-leading mileage and proven class-leading mid-corner grip and wet and dry braking performance on bitumen.

"Pub wisdom suggests on-road manners can come at the expense of off-road performance, but the OPAT II with its unique aggressive sidewall bites through the toughest ruts or soft sand and is as hard as nails.

"Exceptional case strength makes them ideal for motor sport, such as the Australasian Safari or Finke Desert Race."

He said there was also "severe service" A/T tyres, such as Toyo's M55.

"The M55 is designed for rocky conditions where high loads are common, such as the mining or exploration industry."

Severe service A/T tyres usually have a higher off-road percentage compared with the industry standard for an A/T, typically 50/50 on road versus off-road.

At the rugged end of the spectrum are the M/Ts.

The wide, deep tread pattern is designed for situations where other tyres run out of grip.

Tackling snow, sand, rocks, gravel and, of course, mud, M/Ts are built for the "path less travelled".

"But we have a lot of reports of Toyo Open Country M/T on daily commutes that see plenty of road use," Mr Burke said.

"Most people who drive on M/Ts daily know the headache of 'highway hum', especially on tour.

"The OPMT is designed to be much quieter, after all, there is bitumen between every adventure."

Tom McKenny

Tom McKenny

is the national machinery writer for Fairfax Agricultural Media


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