Originally Posted by
FBinNY
First of all, understand that tubes don't have seams. What looks like a seam isn't one at all, it's a raised line resulting form the seam in the mold. The tube's rubber is perfectly continuous below that line.
This kind of split usually happens when an improperly seated tire blows off the rim.
Agreed. Another possibility is a casing failure in the tire. Bottom line: if the tube is properly contained within the tire's casing, a blowout like that cannot happen. The tube either was protruding under the bead, as FBinNY suggests, or the casing failed, allowing the tube to escape the tire and burst.