6 yr old tires with good tread. Safe? or time to replace?

that just depends, are they dry and cracked or does it still look like a new tire? check the sidewalls and in the lines of the tread for cracks or dryness. I'd say that as long as it's not dried out or cracking that they're most likely good, maybe not show worthy, but should be safe to drive on.

Hi, Sitting for 6 years could lead to misformation of the rubber, rotating with a flat spot causing vibration. If this have not happenned, stretch you dollar.