Looking for insight into exactly how our rear tire failed today.
Background: Co-Motion speedster, Rolf Tandem wheels, 25mm Conti Gran Prix 4-Seasons tires, inflated to 120 PSI. Team + Bike weight ~ 300 pounds. Rear tire is relatively new, perhaps 200 miles of use. Good history with Gran Prix 4-Seasons for us, no known issue.
Failure reconstruction: We're riding a 1.5 mile stretch of freeway to get home. Good shoulder with moderate amount of debris. Rumble strip is present adjacent to traffic lane. Lots of traffic on the freeway. This segment starts downhill, then is flat to our exit. We're travelling 32.6 MPH when the rear tire blows. I hold the bike neutral and don't brake, but the rear wheel starts to come around to the right, causing the bike to start to move left. I know if we get into the rumble strip it's "game over", but I am able to steer the bike back to right and coast it to a stop on the shoulder. Stoker was super-smooth throughout the entire event - I wouldn't expect anything less from her though our adrenaline was pegged.
We were able to boot the tire and put a new tube in to get home. Inspecting at home we found the following:
I don't believe we hit anything, I certainly didn't feel any impact. My best assessment is the tube blew for unknown reasons and the force dislodged the circular portion of the tread (no damage to the cords existed at the time of the flat, the fraying seen was caused by the 10 mile ride home).
Open to alternate theories or experience.