To get the most life and performance out of your tyres, keep them inflated at the right pressure. Incorrect pressure changes the contact your tyre has with the road. This affects handling and braking.
Under-inflation can cause:
- Excessive tyre flexing - a key cause of catastrophic tyre failure
- Accelerated and uneven tyre wear
- Increased fuel consumption
Over-inflation can cause:
- Harsh ride
- Uneven wear
- Increased risk of tyre impact damage
So what's the correct pressure?
All cars built since 1973 have a tyre placard that lists:
- the size of the original tyres fitted to the car
- 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.
What’s on the tyre placard?
- Minimum allowable cold pressures
- Pressure shown in Kilopascals (kPa) and often in pounds per square inch (PSI).
Conversion = 7kPA = 1PSI
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
- It is 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 is 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.
Tips to remember when checking your tyre pressure
- You can inflate your tyres to the max numbers shown on the placard
- Check tyre pressure when your tyres are cold
- Don’t bleed air from hot tyres
- Replace the valve dust caps after checking tyre pressure
- Increase tyre pressure if you’re carrying an increased load or you’re driving at high-speed
- Complete fortnightly pressure checks with your own tyre gauge
- If you notice a pressure drop, especially in one tyre, it’s worth getting it checked for a puncture or defective valve
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
The markings on tyres provide lots of information on the type, loadings and dimensions of your tyres.
A – The brand, make and model of the tyre
B – Section width
These three numerals show the tyre width in millimetres. This is the total inflated width at its widest point (excluding sidewall ribs and lettering). The ‘P’ indicates this is a tyre for a passenger car
C – Aspect ratio
This number shows the height of the tyre by expressing it as a percentage of the section width. A P205/60 tyre shows the section width is 205mm and the height is 60% of that. The lower this number, the lower the tyre profile. The typical ratio is between 50 and 75, although high performance tyres can go as low as 30.
D – Construction
This single letter shows the type of construction. R stands for radial, B for Bias.
E – Rim
This number represents the rim diameter which fits the tyre. This measurement is always in inches.
F – Load
This number is checked against a chart to identify the maximum load the tyre can carry at the speed indicated.
G – Speed
This symbol is determined by the maximum safety speed. Passenger tyre speed ratings start at N (140km/hr) and go through to Y (300km/h).
If you'd like peace of mind that your tyres will last the distance, an RACQ Vehicle Inspection can help you out.Call us on 13 1905.