Why don't your tyres explode

[flapsforty]

M.Mouse, regarding your question about exploding; an other type of explanation.

Breath in at depth and the pressure in your lungs equals the water pressure on the outside.
Go up without exhaling and the decrease in pressure will allow the air to increase in volume.
If you breathe in at depth and hold your breath while ascending you will in fact "explode" your lungs.
Which is why many diving schools hammer it into the newbies' skulls to make a continuous sound during ascent; this makes exhaling madatory and avoids lung injury.

And what's so complicated about them tires huh?