Tires: Cracks inside the Tire Treads, Tire Cracking, Dry Rot

Question
Hi - About 3 years ago I bought a set of Michelin tires from one of the wharehouse chains (ie BJ, Costco, Sams etc).  25K miles later, according to my mechanic who is very reliable, I have cracks inside the tire tread.  He called them dry rot.  Oddly, only on two of the four tires.  I went back to the wharehouse and was told two things: 1) would not be covered under warranty anyway - especially if it was dry rot, and 2) they are "stress" cracks and unless you can see through the rubber to the material beneath, I should not worry - it is normal wear and tear on todays multi-material tires.  Either way it would not be covered, nor could he pro-rate a new set.  I trust my mechanic but don't want to spend 400-500 dollars on a new set.  Any thoughts?  Thank you in advance for your time and consideration.

Answer
David,

Rubber is an organic material and it loses its properties over time.  This comes out as cracks - which are a combination of the material properties and the amount of stress the material is subjected to.  "Dry rot" is sometimes used to describe this, but the term should more properly be used for tires that don't see service much and are cracking due primarily to how old the tire is - rather than the amount of stress the tire experiences.

I think "dry rot" is overdiagnosed.

Plus Michelins seem to get cracks in the tread more readily than other brands.  So I am tending to side with the warehouse.

However, you should be aware that many tire manufacturers are issung bulletins to the effect that tires should be removed simply because of age.     My take is that 6 years is the limit for hot climates (AZ, CA, NM, TX, NV, and FL) and 10 years is the limit for cols climates (MT, MN, WI, ND, etc.)

So If I were you I would keep and eye on the cracking - and depending on where you live, replace the tires based on the limits I just mentioned.