Ahead of our monthly appearance on WBZ-AM1030 tonight, we got a text from host Bradley Jay: “Are these tires ok?” he asked. The pictures revealed that all was definitely not ok, and it had nothing to do with tread depth. Age was the culprit.
The tires photos Bradley sent are from a 2003 Jeep Liberty. It’s had at least one tire replacement since it was new, but Bradley couldn’t remember the last time the tires had been replaced. He noted that there was plenty of tread life left.
The issue, though, is the presence of cracks in the rubber, where the tread blocks meet the sidewall. The tires are a perfect example of a condition called “dry rot” and if it’s showing up on your tires, you need to replace them immediately.
To understand dry rot, you need to understand what tires are made of. The rubber portions of tires are constructed of styrene-butadiene rubber. The compounds differ based on their applications. The tread, for example are extruded with four or more different components, usually a base compound, core compound, tread compound, and wing compound.
Each rubber compound is made up of five components in slightly varying volumes: styrene-butadiene rubber, carbon, zinc oxide, stearic acid, accelerator and oil. There are also various chemicals that help the tires resist UV, ozone and oxygen exposure, but make no mistake: exposure to the elements starts killing tires the moment they come out of the molds.
Oils and chemicals in the rubber begin to dry out and break down, and the rubber begins to lose its flexibility, turning almost plastic instead of rubber. As the tire rolls, it stresses weak points in the rubber, and cracks begin to develop. In severe cases, chunks of the sidewall can separate from the inner liner, and the tread itself can separate in a complete piece.
Ironically, lack of use is more the issue than overuse. Tires that sit don’t go through the heat cycles an well-used tire does, and it leaves them more susceptible to dry rot.
The life span of an average tire is six years, regardless of mileage. Once tires hit that age, the rubber compound begins to harden, and the rubber is more likely to crack. It also doesn’t grip the road surface the way it did when it was new.
To check the age of your tires, look for the manufacturing date located on the sidewall.