If you want to geek out on tubes, here you go: Although this type of explosion is usually the result of a section of tube being stuck between the bead and rim, excessive pressure can force a bead off a rim, and when the tube escapes it expands and explodes. (BTW a tire set up tubeless will come off a rim much easier because inner tubes tend to force the bead to stay under the rim hook). Tires do in fact get bigger in diameter as pressure increases, but not enough to damage the tube. Factories have cost-cutting tricks to produce cheap tubes, including; 1) inexpensive additives to make the butyl rubber "go farther", 2) the extrusion process is sped up, causing the wall of the tube to vary excessively, resulting in thin spots, 3) inadequate filtering of the butyl, leaving granular contaminants in the rubber, which cause pinhole failures, 4) cheap or poorly controlled valve production resulting in rubber around the valve not galvanizing properly with the rest of the tube, which is why you see "cut" failures around there. Tubes do deteriorate over time, especially if left in the sun. Using a tube that is slightly undersized is generally not a problem if the quality is good, although if extremely undersized, you will feel the area around the valve as a *whump* when you ride, because that area is reinforced and does not stretch as much as the rest of the tube.