Tyres: What Pressure to Use and When to Replace Them?
The door frame on the driver's side shows a pressure figure that differs from the one moulded into the tyre itself. Here we explain which one to follow, how to measure tread depth with a one-euro coin and why the 1.6 mm legal limit is not the figure you should be watching.
Where to find the recommended pressure
The correct pressure is shown on a sticker, usually on the driver's door pillar. If it isn't there, check the fuel filler flap, the glovebox or the car's handbook.
It rarely gives a single figure. There is one column for driving with a light load and another for travelling with luggage and every seat occupied. On top of that, the front axle often requires a different pressure from the rear.
The most common mistake: inflating to the sidewall figure
Many people inflate their tyres to the number shown on the tyre's sidewall. That figure is the maximum pressure the tyre can withstand. It is not the recommended pressure, and it is usually far higher.
At that pressure the tyre becomes hard. Less rubber is in contact with the road surface, and braking suffers. The figure that counts is the one on the car's sticker.
Cold and warm pressure
The figure on the sticker is intended for cold tyres, meaning the car has been parked for a good while or has only covered a very short distance.
As you drive, the air heats up and the pressure rises. If you pull into a petrol station after a long journey and let air out to the exact figure, your tyres will be underinflated once they cool down. When the tyres are warm, many manufacturers advise adding around 0.3 bar.
Even without a puncture, a tyre loses some air every month. That is why it is worth checking the pressure once a month.
How to measure tread depth with a one-euro coin
The gold outer ring of a one-euro coin is about three millimetres wide. Insert the coin edge-first into one of the tyre's main grooves. If the gold ring disappears completely into the groove, you have more than three millimetres left. If it is visible, you are below that.
Repeat the test in the centre and on both sides of the tread, on all four tyres. Wear patterns also offer clues. If the centre is worn, the pressure is too high. If both edges are worn, it is too low. If only one edge is worn, have the alignment checked.
The 1.6 mm legal limit
The tyre itself marks the legal minimum. On the sidewall there is a small triangle or the letters TWI. In line with that marking, inside the groove, there is a 1.6 mm rubber bar. Once the tread is worn down level with that bar, the tyre is no longer legal.
This minimum was set by a 1989 European directive for the whole Community. In Spain, driving below it can result in a fine for each tyre. At the ITV vehicle inspection, it is a defect that causes the car to fail.
Why it is worth replacing them at around three millimetres
The 1.6 mm limit does not tell you when a tyre starts to fail. It tells you when it has already lost much of its capability.
The grooves channel water away from beneath the rubber. The shallower they are, the less water they can clear. In heavy rain, the tyre can end up riding on a film of water. In addition, wet braking distances increase noticeably well before the legal minimum is reached.
That is why many manufacturers and independent tests put the recommended replacement point at around three millimetres. This matches the gold ring on the euro coin. The law tells you where the fine begins; the coin tells you when it is time to change your tyres.
Frequently asked questions
Which pressure should I use: the one on the door or the one on the tyre?
The one on the car's sticker, usually found on the driver's door pillar. The figure on the tyre's sidewall is the maximum pressure the tyre can withstand, not the recommended one.
Can I check the pressure after a long journey?
The recommended figure applies to cold tyres. When the tyres are warm, many manufacturers advise adding around 0.3 bar so they are not underinflated once they cool down.
How do I know if my tyres have more than three millimetres of tread?
Insert a one-euro coin edge-first into one of the main grooves. If the gold ring disappears completely, you have more than three millimetres left; if it is visible, you are below that.
What happens if I drive with less than 1.6 mm of tread?
In Spain, it can cost you a fine for each tyre. It is also a defect that causes the car to fail the ITV vehicle inspection.
Informative article written with the help of AI tools from the verified script of the video. The video is in Spanish.