Buying a quality car and maintaining it properly will keep you rolling along, but what you put on your wheels really makes a difference. Your tyres, after all, are where the rubber hits the road. Putting cheap tyres on an otherwise solid automobile would be like wearing thongs with a tuxedo.
Chances are you'll need to buy new tyres every few years. Generally speaking, they're all round and black, so it's not easy to predict how well they'll do their job by just looking at them – or kicking them, for that matter.
Each tyre varies in its tread pattern and rubber mix, and is a compromise between a number of requirements, such as grip and durability. Generally, a soft tyre provides better grip but also leaves more rubber on the road, so won't last as long as a harder model. Racing tyres are an extreme example: they're very soft and practically glue the car to the track, but may only last for part of one race – if that.
CHOICE's cornering and braking tests assess the grip of tyres, but durability is not easily measured. Some tyres have a US tread wear rating that can give you some idea of how long a tyre should last compared with others used in the same conditions.
Rolling resistance relates to the amount of energy needed to move a vehicle along the road. Theoretically, the lower the rolling resistance, the less fuel required. There's no single consistent testing method used by manufacturers to measure rolling resistance or to determine how it relates to fuel economy. With some manufacturers claiming up to 10% better fuel economy with low rolling resistance tyres under certain driving conditions, we have developed a method to test this for ourselves in addition to our regular braking and cornering tests.
Each tyre has standard markings to help you pick the right size and type for your car. It's a confusing mix of letters and numbers, and measurements in millimetres and inches.
Here's what it all means, using the code for one size we recently tested: P175/65R14 82H.
- P stands for passenger tyre.
- 175 is the section width (in mm) when the tyre is fitted to the recommended rim, inflated to the recommended pressure, and not under load. The section width is the distance between the tyre's exterior sidewalls.
- 65 is a percentage describing the tyre's profile, or aspect ratio. It's the ratio between the tyre's section height (distance from the wheel bead seat to the top of the tyre) and its section width – in this case, 65%.
- R stands for radial, which is the most common construction method for passenger car tyres.
- 14 refers to the diameter (in inches) of the rim the tyre should be fitted to.
- 82 is the load rating index, which tells you the maximum weight one tyre can carry (in this case, 475kg). Other examples: 84 (500kg), 86 (530kg), 89 (580kg), 92 (630kg), and 94 (670kg).
- H is the speed rating index and tells you the maximum speed at which the tyre can travel (in this case, 210km/h). Other examples: S (180km/h), T (190km/h), V (240km/h), and W (270km/h).
Tyre models that are marketed in the US must have a tread wear rating as part of the Uniform Tyre Quality Grading system (UTQG). If the same tyre is available here you can use the information too – it's printed on the tyre sidewall.
Under the system, a tyre's tread wear is measured under controlled conditions involving an 11,500km drive on a specified test course, and compared with a "standard" tyre with a rating of 100.
For example, a rating of 200 indicates that the tyre should last twice as long as the standard model. So the higher the number, the longer you should expect a tyre to last. The rating is purely comparative.
Real-life wear of a tyre depends on a number of variables, such as road surface, tyre pressure, wheel alignment and driving style. A tread wear warranty is a more reliable indicator of the life of the tyre.
Also part of the UTQG (and printed next to the tread wear rating) are:
- a traction rating that grades the tyre's wet braking traction (AA, A, B or C – where AA is the best), and
- a temperature rating, which indicates a tyre's ability to dissipate heat (A, B or C – where A is the best).
- Some tyres are directional, which means they're designed to be fitted to the car so their tread pattern faces a particular way (usually marked with an arrow on the sidewall). Fitting them on the wrong side may affect the car's handling and reduce the tyre's life. If you use these and don't have a conventional tyre as a spare, be aware that a directional spare only fits one side of the car. If you have to use it on the wrong side, drive carefully and replace the damaged tyre as quickly as you can.
- Don't confuse directional tyres with asymmetric models (or Outside/Inside) designed to be fitted to the rim so that a particular side (marked on the tyre's sidewall) faces outwards. With these, the spare can replace any of the other tyres. You can identify these with the word "Outside" printed on the tyre rim that is designed to be faced outwards, and "Inside" printed on the side that is designed to be faced inwards.
- Some car models have a space-saver (narrower) spare tyre instead of a full-size one. If you have to use it, follow the instructions in your user's manual. There's likely to be a speed limitation, and you're only supposed to drive on it for a short distance to get you home or to the nearest tyre fitter. If you use it over longer distances or at higher speeds, you may damage your car.
All tyres are stamped with the date of manufacture. You'll see this in two varieties: three digits for pre-2000, and four digits for after 2000. (We're assuming you've changed your tyres since the turn of the millennium, but it's good to know this stuff just in case.)
- Pre-2000 the first two digits stand for the week in the year and the last digit stands for the year. So a three-digit number of 078 stands for the seventh week in 1998.
- After 2000 the first two digits stand for the week in the year and the last two digits stand for the year. So a four-digit number of 0209 stands for the second week in 2009.
Tyre pressure is measured in kilopascals (kPa) or pounds per square inch (psi). Keep your tyres inflated to the pressure recommended by the car manufacturer – usually shown on a sticker inside the driver's door frame, in the glovebox or on the petrol tank flap.
- The car manufacturer's recommendations refer to the pressure when the tyre is cold, not after you've been driving for some time – so do your check at the petrol station down the road, not halfway through your journey.
- When driving with a heavy load such as a trailer, inflate your tyres to a higher pressure – again, check the manufacturer's instructions.
- Driving with under-inflated tyres uses more petrol, adversely affects the car's handling and may lead to tyre damage.
- Check the pressure regularly – make it a habit each time you fill up with petrol, or invest in your own tyre pressure gauge.
- Don't forget to check the spare's air pressure when you do the other tyres.
- When you check the pressure, also do a visual check for objects embedded in the tread, such as stones or glass.
- Check for uneven wear, which could indicate a problem with the car's steering or suspension.
- Run your hands over the tread and sidewalls to identify any bubbles, cuts or cracks.
- Keep an eye on the tyres' tread wear indicators, which show the minimum legal tread of 1.6mm. The indicators are small bars spaced across the grooves of the tyre's tread pattern. Replace your tyres when the tread level reaches the indicators – at the latest.
- Rotate the tyres regularly – for example, at every service.
- When putting on new tyres, have them balanced and a wheel alignment done.