K-9 KEVLAR: Kevlar is a synthetic fiber that is about five times stronger than steel. Kevlar is used in tires in one of two ways: as a replacement for the steel coils that form the tire's edges (known as beads), or as sub-tread, which is a protective layer that rests between the external rubber and the internal fabric casing that forms the tire's structure. When the beads are made of Kevlar, the tires are lighter (by around 2 ounces or 56 grams each) and the tire can be folded up easily, something that can't be done with a regular tire. When the casing or sidewalls include Kevlar, there is some added weight and a somewhat more rigid ride, but often these tires can go a year or more without a flat because of Kevlar's ability to deflect glass and other sharp objects and defend the tube against puncture.
