Here’s a little something on flat tires courtesy of Wikipedia.

Having flat tire may cause the rim of the wheel to ride on the tire tread or the ground, and may result in loss of control of the vehicle or irreparable damage to the tire and wheel.

The most common cause is puncturing of the tire by a sharp object, such as a nail, thereby letting air out. Depending on the size of the hole, the tire may deflate slowly or rapidly.[1]

Other causes of flat tires include:

• Failure of or damage to the valve stem through which the tire is inflated.
• Sometimes, a tire may be flattened through acts of vandalism. Examples of this can be as simple as letting air out through the valve stem, which is easily repairable by simply refilling the tire, to slashing the sidewalls, which may require the whole tire to be replaced.
• A tire may be damaged in a collision with another vehicle or an object that causes the rubber of the tire to separate from the wheel, or that rips the tire to shreds.
• Excessive wear of the tire tread to the point where even blunt stones or imperfections in the road may tear a hole in it.

While some flattened tires, particularly those caused by a slow leak, can be repaired and re-inflated with air, others, especially those from worn tread, must be completely replaced.