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Tyre FAQs

For many motorists, tyres barely rate a second thought, until one goes flat or they need to be replaced. However, with a little care and attention, tyre life can be maximized.

How long should tyres last?

Tread wear is affected by many factors. “Enthusiastic” driving styles, including high speed operation and cornering, harsh braking and hard acceleration all dramatically reduce tyre life. Factors such as load, road surface, climatic conditions and tyre and car design also play a part.

When is a tyre worn out?

The law requires a minimum 1.5 mm tread depth across the face of the tread normally in contact with the road. To help gauge this, car tyres have tread wear indicator bars moulded across the tread at regular spacings. When the tread block is level with the wear bar, the tyre is at its legal limit. Tyre grip on a wet road diminishes considerably as the tread wears so tyres should be replaced well before they reach 1.5 mm. Remember also that cuts or other damage can render a tyre unroadworthy too.

Can a tyre be too old?

Some industry experts suggest that worn out or not, a tyre may have passed its useful life after about five years, however this is not recognised in law. A production date code is moulded into the tyre sidewall. A tyre dealer can assist with interpreting the code.

What size tyres are right for my car?

The recommended sizes, speed and load ratings are shown on the car’s tyre placard and in the owner’s handbook and we recommend sticking with what the manufacturer specified. However, there is some latitude allowed. See section 4 of Queensland’s Department of Transport and Main Road’s modification code of practice LS for more details. Find out more on choosing new tyres for your car.

Alternative wheels and tyres

Fitting alternative wheels and tyres to passenger cars is one of the most common and popular of car modifications and there are definite rules you must follow when selecting them. They are set out in section 4.2 of code LS of Queensland’s Department of Transport and Main Road’s modification code of practice.

What’s the best replacement tyre?

Tyre engineering is about compromises and trade-offs. It simply isn’t possible to design a tyre to do everything well. For example:

  • High performance tyres that offer high levels of grip are often quite soft and can have a short life.
  • Tyres that have chunky tread patterns to displace water can provide high levels of wet grip but are often noisy.
  • Tyres that wear well may not have the same level of grip as a “softer” tyre.

Ultimately, you’ll need to consider what’s important to you and discuss your needs with a reputable tyre dealer. As a general rule though, if you stick with well-known brands you shouldn’t go too far wrong. Remember also that you usually don’t get anything more than what you pay for, so skimping on tyre quality could be false economy.

Mismatched tyres

Do you only need to replace one or two tyres?

Mixing of tyre brands (but not carcase construction) is permitted under Queensland law, but we don’t recommend it as it can dramatically alter a car’s handling characteristics. For safety sake only fit matching tyres. Additionally, the drivelines of some 4WD and AWD cars can be damaged by fitting mismatched tyres, and some manufacturers only recommend fitting a full set of matching replacements. If in any doubt about the appropriate course of action, seek advice from a dealer.

Run flat tyres

Run flat tyres are capable of limited operation when deflated. They are typically only used by a few manufacturers. Their advantage is that the car manufacturer can dispense with a spare wheel. Disadvantages are:

ullet">ride quality can be compromised
  • replacements may not be immediately available
  • they cost more
  • they require special equipment to remove and refit

Low rolling resistance tyres

An increasing number of car manufacturers are fitting low rolling resistance (LRR) tyres to their ‘green’ models.

  • It’s claimed they reduce fuel consumption by 2 to 3 percent
  • Increasingly, tyre manufacturers are expanding their ranges to service cars that were not originally fitted with them.

Retread tyres

Retread tyres were once a commonly used, low cost option to new tyres. However, they are now rarely used as the price of new passenger car tyres has significantly decreased.

Caring for your tyres

Caring for your tyres is easy. It only takes a few minutes every couple of weeks to get the best out of them.

Inflation pressure

Correct inflation pressures are essential if your tyres are to deliver maximum life and optimum handling and braking performance. Under inflation causes:

  • excessive tyre flexing (a key cause of catastrophic tyre failure)
  • accelerated and uneven tyre wear
  • heavy steering
  • increased fuel consumption.

Over-inflation can result in:

  • harsh ride
  • uneven wear
  • increased risk of tyre impact damage.

So what’s the correct pressure?

All cars built since 1973 were fitted with a tyre placard that lists:

  • the size of the original tyres fitted to the car/li>
  • their speed and load ratings
  • recommended inflation pressures
  • the original wheel specifications
  • optional wheel and tyre specifications (where offered)

The placard is usually inside the glove box lid, fuel filler flap or on the driver’s door or opening. The information is also in the owner’s handbook.

Tyre placard shows correct tyre pressures

Tyre pressures are measured in Kilopascals (kPa) or in pounds per square Inch (PSI). Conversion: 7kPa = 1 PSI The pressures shown are generally the minimum required for normal city driving with minimum loads.

  • For load carrying or sustained high speed driving pressures should be increased as recommended by the placard or a reputable tyre dealer
  • It is acceptable (even wise) to use the high load / speed pressure at all times

*Tyre pressures should be checked cold.

  • its normal for pressures to increase as the tyre heats up from driving
  • don’t bleed air from hot tyres to obtain the recommended cold pressure
  • it’s a good idea to have your own tyre gauge for doing regular pressure checks
  • check tyre pressures at least once a fortnight
  • don’t forget the spare
  • significant and persistent pressure drop, especially on just one tyre, suggests the possibility of a leak which needs to be investigated
  • always replace the valve dust caps. They help seal air into the tyre and exclude dirt.
Nitrogen for tyres

Has someone suggested filling your tyres with nitrogen? See what we have to say about it here.

Wheel alignment, wheel balance and tyre rotation

Worn steering and suspension components and incorrect wheel alignment and balance all influence how long a tyre lasts so it’s a good idea to watch for the development of uneven tread wear patterns while checking tyre pressures. If you notice any problems, have your mechanic check further.

For most cars, regular tyre rotation is also recommended to achieve best tyre life.

Don’t forget to have the wheels balanced too to prevent annoying steering vibrations and uneven tyre wear.

Understanding tyre markings

Tyre sidewall markings may appear confusing, but once you know the code, they provide a wealth of useful information.

Diagram of tyre markings on sidewall

Source: Australian Tyre Manufacturers' Association

The following information relates to a typical passenger car radial tyre.

Check the diagram to find the following:

A – The brand, make and model of the tyre.

B – Section width

The section width is the total inflated width, in millimetres, at its widest point (excluding sidewall ribs and lettering) – the diagram below will make this clearer.

The letter "P" will sometimes precede the numerals. This signifies it’s a passenger car tyre but is now rarely used.

Diagram of cross section of tyre

Source: Australian Tyre Manufacturers' Association

C – Aspect ratio

The second number is the aspect ratio or profile of the tyre. This is the section height of the tyre, expressed as a percentage of the section width. E.g. in the case of a P205/60 tyre, the section height is 60% or the section width (205mm). The lower this number the lower the tyre’s profile.

D – Construction

The single letter designates the type of tyre construction –R stands for radial.

E – Rim diameter

This is the nominal rim diameter (in inches) for which the tyre is designed.

F – Load index

This index number is checked against the load chart below to determine the maximum load, in kilograms, the tyre can carry.

G – Speed rating

This symbol is also decoded by referring to the speed chart below to determine the maximum speed to which the tyre has been safely tested.

Load Chart:

Tyre Load Ratings
Load Index KG Load Index KG
75 387 98 750
76 400 99 775
77 412 100 800
78 425 101 825
79 437 102 850
80 450 103 875
81 462 104 900
82 475 105 925
83 487 106 950
84 500 107 975
85 515 108 1000
86 530 109 1030
87 545 110 1060
88 560 111 1090
89 580 112 1120
90 600 113 1150
91 615 114 1180
92 630 115 1215
93 650 116 1250
94 670 117 1285
95 690 118 1320
96 710 119 1360
97 730 120 1400

Spare wheels and tyre repairs

At one time a car’s spare wheel was identical to those on the road. However, manufacturers are increasingly supplying some form of temporary use spare wheel that differs in appearance and size to those on the road, or no spare at all.

When a temporary use spare is in use the car is subject to operational limitations, such as a maximum speed of 80km/h. There may also be other requirements such as the position on the car where it can be fitted and / or a maximum distance it can be used.

Tyre sealants and “inflator kits”

Tyre sealants definitely do not provide a permanent repair. Even those supplied with cars as original equipment (sometimes called inflator or mobility kits) are only intended to seal small punctures to allow the car to be driven carefully to a repairer. They generally won’t work on more seriously damaged tyres.

Some sealant kits have a definite shelf life after which they need to be discarded and replaced.

Be cautious of sealant products that are put into tyres as a precaution on the basis that they will prevent flat tyres by sealing punctures as they occur. Even if they do work as claimed, there is a very real risk that they can mask potentially dangerous tyre damage.

Tyre repairs

Tyre repairs are only allowed in the tread area and are best performed by a reputable tyre dealer who can properly assess if it’s safe to repair.

  • In all cases the tyre must be removed from the rim to check for internal damage.
  • Punctures in tubeless tyres must only be repaired by fitting a vulcanized plug or patch from the inside of the tyre.
  • Plugs fitted from the outside are not a permanent repair.