The tires do age and I would be cautious using them if they are that old. The sun and weather conditions age the tires. They are supporting the front end weight of your towed car. I would change them out with new ones at this point. I just bought a tow dolly and have extra tires that came with it in the deal. I wrapped them up and placed them inside my garage out of the elements to keep them as fresh as possible for future use.
Paul
__________________
|