The importance of tyre tread depth is well publicised, but other factors influence tyre safety too. A study by Kwik Fit and Michelin found that as many as 27.6 per cent of cars had at least one tyre "dangerously" underinflated – while a further 12 per cent had at least one classed as "very dangerous".
The study, carried out in supermarket car parks, surveyed more than 500 vehicles. The companies classified tyres according to how far below the manufacturer's recommendations they were inflated.
Tyres between 7psi and 14psi below the manufacturer's recommendation were 'dangerous', while tyres over 14psi below the manufacturer's recommendation were 'very dangerous'.
Jamie McWhir, technical manager at Michelin UK, said: "Driving around on underinflated tyres costs money and it can cost lives.
"We wanted to team up with Kwik Fit to encourage motorists to check their tyre pressures regularly. It makes sense from a cost and environmental point of view, but more importantly it's critical for the safety of the vehicle, its passengers, other road users and pedestrians."
Michelin says running a car with tyres underinflated by 7psi will knock fuel efficiency by 1mpg. It claims motorists in a large city may be paying around £2 million a year in excess fuel consumption due to underinflated tyres.
Roger Griggs, communications director at Kwik Fit, said: "It's worth reflecting on the fact that a car's tyres are the only thing to connect it with the road and we urge motorists to check their air pressure, tyre condition and tread depth every fornight."