Tire Sidewall problems of the 1998 Mazda B4000

Tire failed while stopped at rest area in mississippi after 8 hours of driving from atl, GA. , side blew out where tread meets sidewall. ( dot number: w2uuipo238 tire size: 225/75r15 ).

During the first year of ownership, I had two tire failures. Both were sidewall separations, occcurring at low highway speed, with no visible cause on the road. These tires weren't warranted, and since the other two were almost new, to match them up, I had to buy 2 new ones from a firestone dealer. Since then I have had no more problems with the tires, but I felt that firestone should have warranted their tires against failure, and there was complete failure along the sidewalls. . I contacted the dealership, and they said there wasn't anything they could do. ( dot number: tire size: p225/70r15 ).