The was a show on TV about tires or how they are made. They said tires are good for 5 years, regardless of wear. Compound in tires breaks down.

I park my truck on a slight grade. I noticed, after about 5 years, rolling resistance. New, they would roll easy. After a few years, they wouldn't roll unless I put the trans in drive. Replaced tires and made a world of difference. Easier to turn and better ride.