Okay, the tires on the Jeep are ten years old. It doesn't see many miles. BFG mud terrains still with 3/4 tread life left, sidewalls looks excellent. No ages signs I can see. Its garaged and the sidewalls see frequent coats of 303. I hate to replace tires that still seem to be in great shape but theres that age thing. If it unsafe I'll bite the bullet. Any tire experts out there?
I spent 30 yrs doing rubber materials and component R&D, engineering and manufacturing at Caterpilar Inc.
For the types of rubber commonly used for tires, weatherstripping and other parts other than oil seals, the big killers are: heat, UV light, oxygen, ozone and petroleum based fluids.
The cracks that develop in tires (weatherchecking) are primarily due to UV light, oxygen and ozone. These factors chemically break the long rubber molecules into shorter fragments. The cracks are the visual evidence of this.
As a practical matter, I do not believe sidewall cracking reduces the strength of the tire directly. However, it can allow water to infiltrate into the reinforcing cords and cables. This can result in the cords and cables unbonding from the rubber. Once unbonded they can act as a cable saw and start cutting into the tire and weakening the carcass.
After the Rubber Tech 101 dissertation, the short answer is: if it were me and there was little or no sidewall cracking, I would run the tires.
I would add that due to the tires age it is even more important to keep them properly inflated and do not overload them. Underinflation and overloading = overheating. Every 18° temperature rise doubles the rate of rubber thermal degradation.
Rubber is organic and does change/degrade over time, even at ambient temp. Sitting in a warehouse for ten years uses up a small fraction of the life of the rubber in the tire.
Regards
Jim
p.s. don't rubber the wrong way.
