Maintaining correct tyre pressures can
optimise tyre life and minimise fuel consumption. However, there are
also compelling safety reasons for doing so, particularly if your
work or recreational pursuits require carrying and/or towing heavy
loads. For example, you might think that because your dual cab ute
has a hefty one-tonne payload rating and 3.5-tonne braked towing
capacity, its tyres as specified by the vehicle manufacturer are
more than capable of handling these loads.
That’s true. However, tyre load ratings are based on the assumption
that cold tyre pressures recommended by tyre manufacturers are
maintained, because they are critical in allowing tyres to evenly
distribute your vehicle’s heavy payload and tow-ball download
through their sidewalls and across their tread faces.
Incorrect tyre pressures can not only compromise your tyre load
ratings but also cause uneven wear, less grip and poor handling.
And, in worst cases, complete tyre failure which can have
catastrophic results particularly for heavily-loaded vehicles
travelling at highway speeds.
So, if you think tyres are just black, round and boring, it’s worth
your safety and that of your passengers and other road users, to
take a little time to understand the importance of correct tyre
under-inflation and over-inflation
Driving on a tyre that’s under-inflated can increase fuel
consumption due to greater rolling resistance caused by more of the
tyre being in contact with the road. However, higher fuel bills are
the least of your worries if you’re carrying and/or towing heavy
Under-inflation can also cause excessive flexing of the tyre
sidewalls (the heavier the load, the worse the flexing) while the
centre of the tread-face can distort to such an extent it becomes
slightly concave and no longer in contact with the road. This not
only concentrates more weight on the outer edges of the tread-face,
causing less grip and uneven wear, but on wet roads can cause the
tyre to skim or ‘aquaplane’ on standing water, losing all contact
with the road and complete loss of control.
This excessive flexing and distortion can also weaken the tyre’s
internal reinforcement and generate excessive heat, which together
greatly increase the chance of a rupture and rapid deflation or
Over-inflated tyres can be just as damaging and dangerous, as the
tread-face can instead ‘balloon’ into a convex shape that leaves
only the centre of the tread in contact with the road, again
reducing grip and causing rapid uneven wear.
Over-inflation can also increase vehicle wear by transmitting more
of the impact from potholes and other road irregularities through
the suspension, which can be particularly bruising when under heavy
loadings. They also create a very harsh and uncomfortable ride.
Over-inflated tyres can be just as damaging and dangerous.
Good tyre pressure
Tyres with even half their recommended pressures can still hold
their shape, particularly light truck and 4x4 tyres with their
robust sidewalls and treads, so visual checks are not good enough if
you’re serious about maintaining correct tyre pressures.
As a general guide, tyres lose about one psi (pounds per square
inch) of pressure each month through natural causes. In other words,
if you started with the correct pressures but didn’t check them for
say six months, they could be at least 6psi below where they should
If that doesn’t sound like much, tests have shown that only a 6psi
difference from recommended pressures can reduce tyre life by
thousands of kilometres. And a difference of 14psi can add a
whopping 14 metres (that’s 3-4 car lengths) to braking distances on
Tyres can also lose pressure due to leaking valves, so always make
sure they are replaced when new tyres are fitted and that all valve
caps are also screwed on tightly to keep out grit that can damage
the valve seals. They can also help to arrest small leaks in faulty
In any case, you should always check and adjust your tyre pressures
at least once a month, but ideally each time you stop to refuel and
always before you set off with a heavy load.
The most accurate and convenient way is with a quality tyre pressure
gauge and portable air compressor, which come in different
configurations and are readily available from automotive retailers.
If you can’t fork out for both of these items, then buy the pressure
gauge and use the free inflation facility at a local petrol station.
That way, you can be sure that your tyre pressure readings are
accurate, as pressure readings at public facilities could be
compromised due to lack of maintenance or damage.
Most importantly, always check and adjust your pressures when the
tyres are cold, either before you leave home in the morning or after
having driven no further than your local service station. That’s
because rolling tyres generate heat and as the air inside gets
hotter it expands and raises the pressures, resulting in false
Finding the right
Cold tyre pressures recommended by vehicle manufacturers are found
on tyre placards, which are usually displayed inside the driver’s
door opening but sometimes inside the fuel filler flap or in your
vehicle owner’s manual.
The tyre placard usually displays two recommended pressures; one for
unladen travel and a higher one for when the vehicle is loaded.
These placards can look more complex on 4x4 and light commercial
vehicles as they often display multiple wheel/tyre sizes for the
same vehicle. So, in those instances, just match the size shown on
your tyre sidewall with the same one on the placard to determine the
Tyre placards are usually displayed inside the driver’s door
opening, inside the fuel filler flap, or in your vehicle owner’s
While reading the information on your tyre’s sidewall, you might
also find a maximum pressure rating which is much higher than that
shown on the placard. That’s because it allows a safety margin for
significant increases in pressure caused by heat.
So, if you inflate a tyre to that maximum pressure rating when cold,
it has no capacity to absorb pressure increases when it heats up,
which could result in a blow-out. So, never inflate a tyre to its
maximum pressure rating!
We hope that’s enough motivation to pay closer attention to your
tyre pressures, particularly if you carry and/or tow heavy loads,
because tyres are the only thing between your heavily-loaded vehicle
and the road. Think about that the next time you’re travelling at
highway speeds and loaded to the max with a heavy trailer in tow.