Then change them! Tyres are the one contact point between a vehicle and the road - so, not only are they critical for handling, but they are one of the most important factors in safety. Most manufacturers recommend replacing tyres 5-6 years, with a 10 year limit being for safety. Seventeen years old is long overdue for a change. You wouldn't catch me driving on tyres that old above 40mph. What do you mean by the markers exactly? Depending on the brand, some tread wear markers are at 3mm, whilst some are right down to 1.6mm. Just because a tyre is legal does not mean it's safe. Of course, that depends on where the car is going (certainly I'd be inclined to change the tyres on a daily motorway car much sooner than a town car). 185/60R14 is quite a common size, so there's lots to choose from. Anything from Conti, Falken, Yoko, Hankook (even Toyo) is worth a look at. Judging by the sounds of it (please correct me if wrong), I would suggest getting the cheapest thing with a brand on it, and call it a day. Certainly, if your dad is getting 17 years from a tyre, I would imagine cornering grip and braking performance aren't of the biggest concern. FYI - I was always told that the only acceptable cracking (not that there really is any) is on the blocks of the tyre. Anything sidewall or carcass, replace. Certainly, cracking on anything suggests that there is likely other issues in the carcass of the tyre.