So how can you tell?

How do you know what type of flat you have? Let's go in order from most to least obvious:

An abrasion is probably the most obvious type, because there will be an abrasion hole through both the tire and the tube. It will usually be visible from a quick inspection of the tire. Smooth tires on "cruiser" type bikes, road bikes or non-knobby "cross" tires on mountain or all-terrain bikes are most vulnerable to abrasions. Knobby tires can suffer abrasion flats, though they are most common in the side walls.

An abrasion that has damaged the tire will usually require a new tire, and probably a new tube as well. However, a small hole in the tube may be repairable with a patch.

A puncture may or may not have a tell-tale sign as you look at the outside of the tire. There could be a tack or piece of glass stuck in the tire. A puncture may cause the tire to suddenly deflate, or it may cause a slow leak, depending on the size of the hole and if the hole remains plugged by the object that made it.

You may only be able to diagnose a puncture by removing the tube and inspecting it. The procedure for removing, inspecting and repairing a tube is provided in the next lesson, "Making the Repair." See the procedure there now, or when you come to that lesson.

A rupture, or "blow out" can usually only be seen by removing the tube from the tire and rim. That is because this kind of flat, considered separately from a rapid deflation caused by an abrasion or severe puncture, usually involves only the tube and not a damage to the tire. Once you see the tube, though, a rupture is pretty obvious and easy to find.

Often resulting from over-inflation, a rupture often occurs along a seam or another weak line in the tube, and it will be large. Unfortunately, the only viable option to repair a rupture is to replace the tube. Fortunately, tubes are not a very expensive purchase, even when you buy one of the special tubes described in the Preventative Measures lesson.