Racing cyclists put an amazing amount of faith in their tyres. After all, they are in contact with the road through just a couple of square centimetres of rubber even as they zoom down mountain passes at 100 km/h.
That faith is well placed. Modern tyres offer amazing grip, combined with light weight and low rolling resistance. But there's still a wide range of options for different purposes.
Let's look at the components of tyres:
Tread: The rubber strip on the outside of the tyre provides grip. Tread is made from various rubber compounds and blends, usually with carbon black or silica added to improve wet-weather grip and increase durability. There is often a pattern moulded into the tread, though experts consider this is actually unnecessary on road bike tyres.
Casing: The body of the tyre is made of layers of fine nylon, cotton or silk threads. The casing holds the tyre together against the pressure of the air in the inner tube. The fineness of the casing is usually expressed in a high number of threads per inch. A high number indicates a fine, more flexible casing and therefore lower rolling resistance (the amount of the rider's effort that goes into pushing the tyre along the road).
Inner tube: A cylinder of rubber with the ends joined into a doughnut, the inner tube seals the air into the tyre. Inner tubes are usually made of synthetic butyl rubber, but for higher performance natural latex tubes are lighter and reduce rolling resistance. However, they are slightly porous, so have to be inflated daily. Inner tubes include the valve. Almost all road bikes use thin Presta valves. Car-type Schrader valves are common on mountain bikes and utility bikes.
Bead: Clincher tyres, the most common type, are held on the rim by the tension in a steel or polymer wire, or bead along each edge of the tyre. Polymer beads are usually made of Kevlar which is lighter than steel and allows the tyre to be easily folded for storage.
An alternative method for mounting a tyre is to glue it on to the rim. Tyres designed for this attachment method are known as tubulars. The tyre is a single doughnut-shaped piece with the carcass sewn together around the inner tube, and the stitching covered by a tape. Glue is applied to this tape and to the rim to join them.
Tubulars are almost exclusively used for racing. They are slightly lighter than clinchers and a properly glued tubular can be ridden while flat for a while if necessary, so a racer can continue riding while waiting for a support vehicle.
Removing the tape and undoing the stitching makes repairing a punctured tubular slow and inconvenient. This makes them impractical for most riders. Nevertheless, tubulars are prized for the smooth feel they impart to the ride of any bike, and some riders choose to use them all the time.
With their easily-replaced, separate inner tubes, clinchers are by far the dominant tyre type. You can get clinchers tailored to all types of riding, from racing tyres that give little away to tubulars in performance, to fat, thick-tread versions with anti-puncture bands for urban riding.