Question

Why does a bicycle tube burst, when overfilled?

Answer 1

This is because when the tube is overfilled, the pressure inside the tube becomes higher and quite unequal to that of the atmosphere. The increased internal pressure is thus the reason why the tubes bursts.

Answer 2

when the tube is filled to its maximum, the pressure inside the tube becomes greater than the pressure outside. the air molecules do not find enough space to move around and thus the tube burst out. especially in hot day when pressure increase further.