here, I concluded it was time to replace one of my Continental Grand Prix Four Season tires, based on damage to the tire casing causing me to distrust it. At that time, I bought two replacement tires. However, being one to stretch the envelope a little, I am still using the survivor, 750 miles later, as my rear tire on Buddy. The second replacement tire is safely ensconced in a dark closet, awaiting its own call to glory. Science is more important than an extra flat. Fortunately for me, tire fairies live in the UK and not Texas. That old tire is sitting right about 5000 miles now. And it looks good. Like maybe I'll get even MORE than the 6000 mile target. Yup, I certainly AM tempting the fates. I need to find some wood to knock on, and maybe toss some salt over my shoulder.