QuestionI have a set of 31 X 10.50 Michelins on my Ranger 4X4 and after four years and about 40,000 miles of use they have plently on tread left. However, they don't seem to have the same traction I recall from the past. Do tires lose traction even thought the tread depth is still good?
AnswerBob,
Rubber, being an organic material, suffers the same aging problems that people do. And one of those things is that rubber "dries out" - gets hard and brittle - over time. You can see some of that in the form of cracks, especially on the sidewall, commonly called "dry rot".
The most recent research I have seen seems to say that time, independently of heat and exposure to ozone, is a major factor in the deterioration of rubber. While I have some problems with this, it at least lines up with my thoughts that there is a time limit beyond which tires are no longer suitable for service.
My current recommendation is 10 years from the date of manufacture and the tire should be taken off. However, 6 years should be used in the following states - AZ, CA, FL, NM, NV, and TX - nad it should be proportionally in between the further north you go. For example, TN = 8.
Hope this helps.
