The Life of Tyres

Have you ever given any thought to the stresses your tyres absorb on any given day? Rolling across kilometres of roadway, carrying thousands of kilograms, plunging through puddles, baking in the sun, resisting forces from braking and torsional loads from acceleration, lateral forces from cornering — and that’s just around town.

Head out into the scrub and the punishment multiplies mightily — sharp rocks, endless distances of battering corrugations, sidewall-tearing stakes, super-heated casings through sidewall flex, and much more.

Tyres cop a lot, and we give them too little thought most of the time. So let’s take a few moments to think about how we may be able to ease our tyres’ burdens and assist them to make our journeys more reliable and less costly.

AGE OF FAILURE

First of all, there is the matter of how old our tyres are. Tyres have a finite lifespan, determined by environment, use and the passage of time. The usage limit will vary between six and 10 years, with the actual length determined by exposure to factors such as sunlight, ozone and usage.

The date of manufacture is indicated by a four-digit code on the sidewall of each tyre. For example, a code saying 0717 means the tyre was manufactured in the seventh week of 2017. The countdown starts from there, not when you fit the tyre to your rims.

Exposure to sunlight and ultraviolet light causes a slow continuation of the manufacturing process of vulcanisation, which is a chemical reaction causing liquid rubber to harden when heated with sulphur and other chemicals at temperatures between 140–160C. This results in cross-links between long molecules of rubber to improve hardness, elasticity, viscosity and weather resistance. As the process continues it makes the rubber harder and more brittle, so the tyre is increasingly more likely to break apart, especially under sudden shock loads.

Exposure to ozone will have a similar effect, so if your tyres are garaged near machinery such as a compressor, where ozone is produced by the electric motor, the rate of ageing will be enhanced.

In more tropical regions, tyre life will be shorter due to higher temperatures and humidity. In places such as Darwin and Cairns, it can be as little as five years. In southern Australia, practical life might be as much as 10 years. If you’re unsure, take your tyres to a tyre professional who will check them for discolouration, heavy cracking in the treads, etc.

What might be a perfectly good-looking set of tyres, if beyond their useable life, could let you down seriously when you can least afford it like at high speeds or on rough roads. Your entire tow setup, vehicle and camper, might be at risk and, in a worst-case scenario, even somebody’s life.

ROTATING THE WORLD

Tyres should be rotated every 10,000km, so it may be a good idea to ask your mechanic to do it during your regular servicing if he doesn’t do it for you automatically.

Tyres need to be rotated from their locations on a set pattern. Front and rear tyres perform different tasks and therefore wear differently, so spreading those demands around will ensure all your tyres get the maximum in life and performance. Follow your vehicle manufacturer’s recommendations.

Note there are what are called unidirectional tyres, which are designed for rotating on their axle in only one direction. These are indicated by an arrow on the sidewall of the tyre. Attempting to swap such tyres from one side of a vehicle to the other should not be done, and they should only be swapped front to rear.

On your camper swap, say, the left wheel to the right side, then what was on the right to the spare and what was the spare to the left. Bringing the spare into use keeps that tyre flexible and ready for use. On a camper, tyres will likely run out of life by age before they wear out.

On your tow vehicle, swap the spare onto, say, the left rear, that tyre onto the front right, the front right, to the right rear and that tyre to the spare position. It’s highly unlikely any vehicle supplied with only a temporary use spare wheel would be used as a tow vehicle, but if for some reason that’s the situation, do not introduce the spare into the rotation cycle. It’s important that 4WD follow a strict regimen of rotation as different tyre wear, which results in differing wheel circumferences, can cause driveline damage.

INSPECTION TIME

While rotating tyres, take a little time for some basic TLC. Clean off any built-up mud or foreign matter. Look for missing wheel weights — most likely on the inside of the rim — and get your tyres rebalanced if they are. Even after wear and tear and without losing balance weights, wheels can get out of balance, so it’s a good idea to do this as a precautionary maintenance item. An unbalanced wheel can cause excessive wear on shock absorbers, springs, bushings and pivot points.

Inspect the tyre tread and sidewalls for damage. Run your hand along the tread. If you feel any feathered edges on the tread, especially on tyres fitted to the front wheels of your tow vehicle or those on a camper or van with independent suspension, you may need a wheel alignment. Pay a professional to do it. Remember, a one-degree misalignment is the equivalent to dragging the tyre sideways 17m for each kilometre of travel.

Clean the wheel stud threads with a wire brush so you can get an accurate torque on the nuts. Do not use grease or other lubricants on the studs or nuts.

After replacing the wheels, torque them to the recommended level and in the recommended pattern to ensure proper seating of the rim on the studs, then check the torque after 100km of travel — you will find most will require nipping up slightly. Make sure your torque wrench is accurate as they can get out of adjustment and give you false readings.

As an aside, don’t expect well-worn tyres nearing the end of their life to give you a trouble-free trip. If you’re planning on that 5000–10,000km trip with plenty of offroad action, have new rubber fitted before you leave. It’ll make for a much happier trip.

UNDER PRESSURE

Tyre pressure is vital to any tyre’s life. There will be an optimal pressure to suit your vehicle or camper on the highway, as well as optimal pressures when offroad on a variety of surfaces. Factory recommended tyre pressures will be displayed on a sticker either in the glovebox, behind the fuel filler cap, on the A- or B-pillar or the driver’s door. The sticker will list the size of the original tyres fitted, their speed and load ratings, recommended inflation pressures, original wheel specifications and any optional wheel and tyre specifications (where offered).

All campers and vans will feature similar information on the compliance plate, usually mounted to the drawbar.

These pressures are for cold tyres, and tyre temperatures will rise with use. Do not attempt to adjust down warm tyre pressures to cold pressures.

The recommended tyre pressures are based on the unladen weight of the vehicle and tyres matching those originally fitted. The pressures are designed to ensure an appropriate contact patch between the tyres and the road surface for proper control of the vehicle. Too high a pressure results in a smaller patch, which might reduce steering and braking performance. Too low a pressure might result in excessive flexing of the tyre sidewall and build-up of excess heat as well as poor performance under braking and steering loads.

The recommended pressures, as stated, are for an unladen vehicle being driven around town at modest speeds. When loaded and/or travelling at higher speed on open roads for sustained times, pressures should be higher.

Offroad, on a gravel surface, tyre pressures should be reduced by about 30 per cent of those for highway use. This permits the tyres to flex more. Pressures should be further reduced for travelling on softer substrates such as sand or mud, even as low as 10 to 15lb (69 to 103kPa), though speed and aggressive cornering should be avoided at such low pressures to avoid rolling the tyre off the rim.

If driving for any extended time with lowered tyre pressures, a check of tyre sidewall temperature to ensure this does not rise too high should be made occasionally. Avoid driving for any extended time on sealed road surfaces with lowered pressures as this will result in increased temperatures which can cause tyre failure.

Carry a portable tyre compressor with you for offroad use. This will give you flexibility if driving on a variety of surfaces away from civilisation. Also sustain a comprehensive tyre repair kit for emergency situations. If you plan on going offroad you will need it at some point.

It is highly recommended that you carry an accurate tyre pressure gauge to monitor tyre pressures. Do not just chuck this in with the other tools. Look after it as its accuracy will govern the optimising of your tyre pressures.

Talk to your local tyre specialist to get a starting point for your tyre pressures and check them regularly. An old rule of thumb is that if your tyre pressures increased by more than 5lb per square inch between cold and hot then your tyres were under inflated initially. If the tyre pressures increased by less than 4lb per square inch, they were too high to start with. This generally works if the two readings are taken in similar ambient temperatures, so don’t take your pressure reading before you leave home early in the morning and then wait until midday to take the warm temperature reading. Do them no more than 20–30 minutes apart so they adequately reflect the pressure increases from the tyre’s change of temperature alone and not from increased ambient temperature.

Correct pressures not only save the risk of a blowout, but a drop of 9 per cent in tyre pressure (which is only 3.5lb per square inch in a set of tyres set on 40lb) increases fuel consumption by 5 per cent.

SUSTAINING PRESSURE

Tyres cop a lot, especially when offroad, and a quality set of tyre pressure monitors can save you a lot of drama.

They’re unlikely to help if you have a catastrophic failure due to age, or if the tyre sidewall is ripped open by a stake or rock, as the tyres will appear OK one minute and be a complete wreck within a second or so, but a gradual leak, or unwanted temperature rise can be telegraphed in plenty of time to enable you to save the tyre and any damage that might result.

Monitors come in sets of 4–10 sensors which replace the valve caps, or are mounted internally on the inner rim, that Bluetooth tyre data (pressure and temperature) back to a dash or windscreen-mounted readout or your mobile phone. If you go for a car-mounted system, look for a suitable mounting system, to avoid adding another bit of clutter to the inside of the windscreen or somewhere else. Sets of more than four can allow you to monitor your camper’s tyres at the same time as your tow vehicle.

Prices range from $40 to $500 plus, depending on the brand, number of sensors and features. Obviously you don’t get much at the lower end, but the better units have saved headaches on many a trip. Look for a system with auto backlighting, the capacity to monitor six to eight tyres to include your camper or van, allows easy disconnect when you unhitch the camper, has a good audible alarm for pressures outside your pre-set minimums or maximums, has a quick and easy reset of pressure optimums when changing tyre pressures, permits different pressure settings for each axle, and has an easily readable monitor display.

There is an argument that temperature readings with external (valve cap) sensors are not as accurate as they can be influenced by external conditions.

Whatever you do, make sure your tyre care is as carefully assessed as you would make that of your brakes, suspension or engine/driveline. They keep your setup rolling happily and can be the source of unwanted angst if they let you down. But then, they don’t really let you down, it’s you that’s let them down.