Tire Tread/belt problems of the 2003 Toyota Sienna

Firestone tires 205/70r15, this is the 3rd tire of 4 that has split. The tread has split away from the belt with plenty of tread left on the tire. I drive the freeway 27 miles each way to work and I could have had a terrible accident. One of the 3 did blow but I was going slow and I did not roll the car.

I was driving home from washington state, and noticed that my driver's side rear tire tread was seperating from the sidewall and steal. My son then found that the passanger rear was doing the same thing. I had to call home and find the closest place to replace the tires. Eugene. Or. Was the closest and it was 49 miles. About 15 miles outside of eugene, the tread on the drivers side was thrown off of my car and caused damage to my van. I regained control and got the car to costco where I replaced all 4 tires.