About 9 years, since I got rid of the crappy Continentals my 2008 Expedition came with and put Michelins on. I used to get a nail or screw in the continentals literally every 5,000 miles. Since then had Michelins and Goodyears on the 2008, and the factory Toyo's I have had for 18 months on the 2018 have been nail free.

I try to maintain my tire pressures. Weather here lately has been going back-and-forth from warm to cold to warm,, etc. A couple days ago it was cold and my dash light up with a tire pressure warning, but I figured it was low pressure due to the cold weather so ignored it and reset the TPMS. Yesterday it warmed up and the dash light up again, so I thought it was now over pressure and reset it again.

Today I went to Direct Tire for a tire rotation and there was a nail in a tire. They patched it for free.

At some point I would have noticed the low pressure - probably when the tire was flat a couple of mornings from now.