Tyre Construction
The vast majority of tyres used on bicycles are known as ‘clincher’ type tyres. Clinchers consist of an outer tire with a u-shaped cross section, and a separate inner tube. The edges of the tyre hook into the edges of the rim and the tyre is held in shape and position by the air pressure in the inner tube. There are also ‘tubular’ tyres. These are glued onto specific rims and have the inner tube permanently sown into the tyre itself. Tubular tyres are mainly used on track bikes.
Tyres are not just made from rubber. In fact, the rubber you see on your tyre is the least important part of the tyre when looking at its structure.
Bead
The bead is the edge of the tyre and is what holds the tyre onto the rim. The beads consist of hoops of strong steel wire, though some tyres use Kevlar® cord instead. Kevlar® is much more flexible and lighter than steel, so tyres with Kevlar® beads help to save weight and can be folded up compactly, which is convenient for touring or other applications where you may need to carry a spare.
Carcass
Cloth fabric is woven between the two beads to form the body, known as the carcass, of the tyre. The carcass is what determines the shape of the tyre. Most carcasses are made from nylon cord, though some tyres utilize other materials.
The fabric threads don't interweave with crossing threads as with normal cloth, but are arranged in layers or "plies" of parallel threads running diagonally from bead to bead. Each layer runs perpendicular to the next layer(s).
Some tyres use thick thread fabric plies, while others use thin thread. With thin thread, there are more threads per inch (TPI). The higher the TPI count, the thinner, lighter and more flexible the sidewall of the tyre is. This results in a tyre with lower rolling resistance, making them ideal for high performance road bikes. Meanwhile, lower TPI tyres, being less flexible and pliable, are heavier and have sturdier and more abrasion resistant sidewalls, which make them ideal for downhill mountain biking.
Some bicycle tyres also have an additional belt of material running under the tread area, in addition to the normal plies. This is intended as a puncture preventive. For more information on puncture protection, Take a look at our puncture protection & prevention article.
Rubber & Tread
Once the fabric has been woven between the beads, and the tyre has its basic shape, it is coated with rubber. The rubber does not really have any importance structurally to the tyre and is mainly there to protect the fabric carcass from damage.
The rubber that comes into contact with the ground is called the tread. This area usually has thicker rubber than the sidewalls of the tyre and has the tread block molded into it.
Most tyres primarily use one compound of rubber. Rubber comes in a range of compounds, ranging from soft, sticky rubbers, which gives more grip; through to very hard rubber, which is more durable and gives the tyre lower rolling resistance. There are also dual-compound rubber tyres. These feature a softer rubber on the outside of the tyre that contacts the ground, and a harder rubber between the tread and the carcass.
Written by: Lewis Thorogood
Hedgehog Bikes Onehunga