Structure of a radial tyre
The carcass of a radial tyre (structure, materials and function)
The carcass forms the foundation of every radial tyre and determines its strength, flexibility and maximum inflation pressure.
In radial tyres, the cord plies are made from materials such as steel, nylon, polyester or rayon. These cords run from bead to bead at a 90-degree angle to the direction of travel. This allows the sidewalls to flex while maintaining a stable tread.
The strength of the carcass depends on:
- the number of cords
- the quality of the cord material
- tensile strength and elasticity
- the number of ply layers
The carcass strength determines the maximum tyre pressure. In turn, tyre pressure and air volume define the load capacity of the tyre.
In agricultural and earthmoving tyres, where volume and load conditions vary significantly, this results in different allowable speeds and load ratings.
Belts, cord plies and tread stability
On top of the carcass lies the belt package of the radial tyre. This consists of two or more diagonally positioned cord layers that, together with the tread, form a rigid structure.
The belt prevents longitudinal deformation of the tread under load and ensures even pressure distribution. This helps maintain optimal contact with the ground or road surface.
As a result, the tyre benefits from improved traction, wear resistance and protection against cuts and impacts.
The tread itself consists of a specific rubber compound and pattern design. Within agriculture and earthmoving, there are major differences in tread design, depth and compound composition.
The tread must withstand deformation, cracking and heavy loads. The combination of belt and tread largely determines traction, rolling resistance and tyre lifespan.
Sidewalls, shoulders and carcass protection
The sidewalls provide flexibility and shock absorption. They absorb impacts, allow controlled deformation and protect the carcass against vibrations and external influences.
The sidewall rubber is elastic and offers protection against cuts, weather conditions and mechanical stress. It also contains key tyre markings such as size, load index, speed index and construction type.
The shoulders form the transition between the tread and the sidewall and play an important role in stability and heat dissipation.
A well-designed shoulder area prevents overheating and deformation, which is essential under heavy loads and demanding field conditions.
Together, the sidewalls and shoulders determine how the tyre behaves under low pressure, high loads and intensive use.
Bead, rim seating and inner liner (TL/TT)
The bead ensures a secure connection between the tyre and the rim. In radial tyres, the bead is reinforced with steel wires and a protective layer to prevent the ingress of dirt or debris.
Mounting earthmoving tyres requires particular care. Excessive mounting pressure can cause the bead to slip over the rim flange, leading to damage.
For tube-type (TT) tyres, an additional rubber layer protects the inner tube from damage caused by the cord plies.
Tubeless (TL) tyres feature an airtight inner liner that seals directly against the rim. This layer is essential for air retention, pressure stability and protection of the carcass.
The choice between TL and TT depends on the application, machine weight and rim design.
Frequently asked questions
What is the difference between a radial tyre and a bias-ply tyre?
A radial tyre has cord plies running at 90° to the direction of travel, while a bias-ply tyre has diagonally arranged plies.
Why is a radial tyre more flexible?
Because the cord plies run perpendicular to the direction of travel, allowing the sidewalls to flex independently from the tread.
Which components determine the stability of a radial tyre?
The carcass, belt package and tread together form the main structural stability.
Why are tyre markings located on the sidewall?
Because the sidewall remains visible during use, making it easy to read specifications during inspection and fitting.
How do I know if my tyre is TL or TT?
This is indicated on the sidewall. TL means tubeless, TT means tube-type.
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