[DanEC]

Lots of variable factors involved in this - no clear answers. I have an old Corvette with about 23 years on the tires (BF Goodrich by the way but not T/As) but only a few thousand miles - sits covered up in the garage mostly - never goes to car shows or sits outside. Still look fine also - but I know I need to replace them. My 2003 Lightning F! Eagles gave up the fight last summer after 15k miles when one developed a leak from a tiny crack in the sidewall. The truck was only used a year for commuting but goes to car shows and Lowe's regularly. With 20K miles I suspect your tires have had a fair amount of exposure to sunlight and ozone but like 1795 said you probably are good for a couple more years. But no guarantees.