Independent tests have shown that cars driving on tyres at the 1.6mm legal tread limit demonstrate a dangerous lack of control in cornering and seriously increased stopping distances on both dry and wet roads.
Commenting on the survey results, Tom Dennigan of Continental Tyres Ireland said: "It was shocking to see that one in six cars surveyed were driving on dangerous and illegal tyres.
"We know that in the current economic climate, motorists have been cutting back on their motoring expenses and some may have been tempted to push their tyres to the limit.
"However, as your only contact with the road, tyres are such a critical element of your car's overall performance, so our advice is don't gamble with your family's safety by neglecting your tyres."
Continental recommends that the optimum time to replace tyres is when they reach 3mm.
Independent tests have demonstrated that once tread depth drops below 3mm, tyre performance drops off sharply.
It is for this reason that public service and emergency vehicles across Europe have their tyres changed once the tread depth reaches 3mm.
In relation to tyre pressure, 53% of cars tested for the survey were found to be on tyres with incorrect tyre pressure: in the vast majority of cases they were under-inflated; and 41% of cars were found to be dangerously inflated.
"Incorrect tyre pressure can affect your vehicle's handling, overall safety, fuel economy and ride comfort, and it is such an easy thing to get right with the correct pressure information printed on the vehicle itself and in the manual," said Dennigan. "Drivers really should take the time to regularly check their tyre pressures and the overall condition of their tyres."