Have a look in your owner’s handbook and see what the correct tyre pressures are for your car, carrying the kind of load you most normally carry. There will be two values: one for the front and one for the back, and they may or may not be equal. Tyre pressures will usually be shown in the traditional ‘psi’ unit (pound/square inch), as well as the EU recognised ‘bar’. You should note both values, because the gauge on the airline at the petrol station you use may show one but not the other.
Some garages still provide free airlines, while others now pay for their upkeep with coin operated units. If you find one of these, you simply insert the necessary coins or tokens, and press a start button, after which you will hear the sound of a compressor running, and the air line will give you a few minutes’ use. Be warned, you will need to work quickly, as these machines often give only 3-5 minutes of air before requiring more coins.
Unscrew the small black plastic cap at the top of the tubular valve protruding from the inner surface of your tyre. It’s often located in a recess in your wheel covers. Push the nozzle of the air line hard onto the threaded end of the tyre valve. You will hear air rush out as the valve opens. Push hard enough until the air stops escaping, and look at the gauge on the airline. The indicator will now show you the pressure of the air in the tyre.
If it is below the correct value, squeeze the trigger on the airline hose, and this will force air into the tyre. You will see the indicator on the air line gauge going up. When it reaches the correct level, pull the air line off the tyre valve. No air will escape as the valve prevents this. Screw the plastic cap back onto the valve. Repeat for each tyre. Every third or fourth time you do this, you should also do the same to the spare tyre.