Tyres

Tyres are important, they should be checked before every trip outside the metro area for tread and just as importantly, pressure.

Tom’s Tips – Tyres

Tyres have a big influence on safety, fuel economy, driver fatigue and traction.

Be aware of the tyre pressures, documented on the tyre placard, commonly mounted on the door frame.

Under inflation

  • Wandery steering due to sloppy side walls Heavy steering
  • Poor handling due to sloppy side walls
  • Reduced fuel economy due to excess drag
  • Excess tyre wear on the shoulders Increase risk of blow out due to excess heating of the air and weakening of side walls.

Of course, Low pressure off road is exactly what you want for extra traction. The exact pressure will depend on the tyre structure (strength of side wall), the load being carried, the speed and the terrain type.

To get the tyre to ‘bag out’ or get to achieve greater surface area, it’s the length of the footprint, NOT the width, that is important here. As you let the pressure down you observe the fattening tyre, but the longer the footprint gets, behind the leading edge of tyre that has the terrain resistance, the better.

Remember Model T fords went all over the outback years ago, one, because they were light, but two, they had 36” tall tyres (4” wide) that when let down had a long footprint.

I had 37” tyres on my GU Patrol wagon, and I started at 13psi when driving south of Robe, just like I do with 31’s. The 37’s were 14.5” wide, so much resistance.

The wider the tyre, the more resistance it gets from the terrain.

Now, another useful hint is to work out what I call the ‘critical pressure’, the pressure of that tyre brand/size/pattern when fitted to your particular vehicle.

The critical pressure is the point at which further deflation will bring about a change in shape, profile, footprint of the tyre. Eg you will find you can drop the pressure 10 or 15psi and traction performance will not have changed because the tyre hasn’t actually changed shape. At the critical pressure, all further deflation will affect the tyre shape, hence footprint, and traction will start to improve. Once you know this pressure you drop straight to it and further, as any pressure higher makes no difference to traction.

When I get a new set of tyres I let one down whilst my knee is resting against it. When the critical pressure is reached I can feel the tyre slipping down past my knee. Then I know.

Over inflation

  • Wears the centre of the tread
  • Reduced braking efficiency as the tyre will tend to skid
  • Poor control in the wet for the same reason
  • Increase wear on steering components as there is less cushioning of the tyre
  • Increase vibrations or harshness of ride
    and feel
  • Increase rear tyre pressure when towing
  • Increase all tyre pressures for hot bitumen

Impact damage to tyres occurs when a hard tyre hits an object, with force or at speed. For this reason:

  • Reduce tyre pressure on dirt roads
  • Reduce tyre pressure on corrugations
  • Reduce tyre on trailers and vans as above The amount of reduction depends on load and speed, the greater these are, the more
  • pressure required.

Guides

  • City
    30 to 34 front
    32 to 36 rear
  • Highway – average temps
    32 to 34 front
    32 to 36 rear
  • Hot weather- over 35 degrees
    34 to 36 front
    36 to 38 rear

With significant load or towing add 2 to 4 extra psi to the rear, probably nothing to the front.

Over 40 degrees, add 2 psi all round to the over 35 pressures.

Dirt roads of poor condition, reduce 10 to 20% all round. And your trailer or van tyres.

A rule that is ALWAYS true – reduce speed to reduce tyre wear and punctures.

Offroad

Wow, this can be an endless discussion.

Another rule that is always true, if the tyre is spinning or slipping, on whatever surface it is, drop the tyre pressures to get more surface area or footprint, to get more grip. And potentially reduce power to allow the tyre to grip, rather than power spinning it. Successful 4wding is about traction, not power. Power is nice to have on hand, we all know that, but if applied too savagely, you actually encourage the tyre to slip.

But I digress.

Mud, I’ve been down to 10, 12, 15 psi plenty of times, but not going hard or carrying a lot of load.

Sand, my lowest ever was take the valves out and wait till I could hardly hear air coming out and move away slowly in a straight line, only 75m then back up to 10psi.

I’ve been to 4, 6, 8 plenty of times when I’m desperate, SA’s south coast Robe to … , bogged down to close the water… just get me outta here! But drive gently and in a straight line away from the danger zone.

But as a general rule, 18 to 22 outback, ie across the Simpson with lots of weight, 13 playing in the Sandhills and in the beaches down south.

Anything less than 13 and the bead will come away from the rim on an aggressive hard turn or bounce off if the front end gets a hard enough hit.

You need a decent reliable compressor, gauge and deflator. And at least a basic tyre plug kit and maybe a bead breaker for bigger outback trips.

GO 4x4 has these in spades. Learn how to use them.

Hint

Remember, when breaking the bead, you’re not stretching the tyre over the rim, you have to position the bead into the narrowest diameter of the rim to allow the outer bead to slip over, with a little encouragement, over the largest diameter part of the rim.

Best of Luck!

Or make it even easier, buy a twin wheel carrier!