Only a quarter of drivers can correctly state the minimum legal tyre tread depth, too.

Two in every five young drivers have no idea how to change a tyre or use a car’s puncture repair kit, a new survey has discovered.

The study by vehicle maintenance firm Kwik Fit found that 38 percent of drivers aged 18-34 can’t fit a spare wheel or use one of the emergency inflation kits provided by some manufacturers in lieu of a spare.

The basic checks that could save lives...

However, the discrepancy between the genders is huge, with 57 percent of 18-34-year-old women claiming that they couldn’t change a wheel. For men in the same age group, the number was 12 percent.

But a lack of ability to change a tyre was not the most concerning finding of the survey, which also uncovered a worrying ignorance of the minimum legal tyre tread depth.

Tyres, which are a car’s only points of contact with the road surface, must have a tread greater than 1.6 mm to be legal for use on the road, but just 27 percent of the 2,000 drivers surveyed by Kwik Fit were aware of that law.

McLaren Pirelli winter tyres

Some 30 percent - the equivalent of 10 million drivers nationwide - admitted that they didn’t know, but one in five drivers (19 percent) said the minimum legal tread depth was 0.5 mm - less than a third the actual limit.

More reassuringly, the average minimum depth quoted by respondents came out as 1.9 mm, which - although incorrect - is above the legal limit.

According to Kwik Fit, many experts recommend changing tyres when they reach 2 mm of tread. The company said this was because “the wet weather performance of most tyres deteriorates well before they get to the legal limit.”

Worn tyres

Roger Griggs, communications director at Kwik Fit, said the alarming findings demonstrated that motorists should be able to carry out basic tasks on “key aspects” of their vehicle.

“These findings show the importance of drivers of all ages having both the motoring knowledge and skills when it comes to the key aspects of their car,” he said. “It is vital that drivers know when their tyres are illegal and unsafe – not least because they could be stopped and fined for driving with tyres that have tread depths under 1.6mm.

“It’s also crucial that drivers are able to change their tyres in an emergency. A puncture can occur at any time, and often in the most inconvenient locations, so if drivers are able to change their own tyre and get on their way, they are likely to be able to save themselves a lot of hassle.”

Tyre safety

To check the depth of a car’s tyre, either use a dedicated tread depth gauge (a ruler will not work) or a 20p coin. If you place the coin in the main grooves of the tyre and the wide band around the outside of the coin is visible, the tyre may need replacing.