Why are bicycle tires inflated?

Yes. Severe over inflation will result in the tire un-beading and blowing off the rim, or even bursting. If this happens while you are on the bike a crash likely will result. Regardless of crash involvement, as the inner tube is blown off the bike, it is usually damaged beyond repair. The result is you have to buy a new tube, and possibly also a new tire. Mild over inflating does decrease rolling resistance (how much energy it takes you to get the tire moving and keep it moving), but, will result in a "harsher" ride. Propper inflation of the tire at factory ratings is always the safest idea for novices. More experienced riders may slightly underinflate or overinflate their tires for terrain, weather, and/or race day reasons. If a tire's beads hasn't seated symmetrically all round the rim, controlled, intentional overinflation can help settle the bead. Once the tire has popped into place the pressure should immediately be reduced to the recommended value. YES. I have a friend who would inflate our tires prior to a run. Several respected makes and models failed along the side wall. We discovered that he was pumping the pressure up to 160 psi then releasing it down to maximum statedon the tire say 120 psi. This overstressed the fibres in the carcass and they eventually failed. He did this with an XP frame pump!