TreadThe thick band of rubber that meets the road. It is made to grip without wearing away too fast.
Lugs (tread blocks)The raised parts of the tread pattern that actually touch the road.
GroovesThe channels round the tire between the lugs. They carry water away from under the tread.
BeltsLayers of steel or fabric cords just under the tread. They stiffen it, so it flexes less and grips better.
ShoulderThe rounded corner where the tread meets the sidewall.
SidewallThe side of the tire, between the tread and the bead. It holds the air in and carries the turning force to the tread. The maker's details and required markings are moulded on it.
Casing plyA layer of fabric cords that gives the tire its shape. It runs from bead to bead inside. In a radial tire the cords run straight across.
BeadThe edge of the tire that sits on the wheel's rim. It seals the air in and holds the tire on.
Bead wiresLoops of steel wire inside each bead. They keep it from stretching, so the tire cannot come off the rim.
How this list was compiled: Read 2026-09-27. (1) US Army, TM 9-8000, Principles of Automotive Vehicles (1985), paragraphs 32-10 to 32-12 and figures 32-10 and 32-11, https://archive.org/details/tm-9-8000-principles-of-automotive-vehicles-1985 : radial tires with casing plies perpendicular to the tread direction and several layers of tread-reinforcing plies (steel or fabric) under the tread; bias plies wrapped round steel bead wires that stop the tire separating from the rim; the tread and its lugs, the spaces between them, rounded shoulders; sidewalls. (2) Wikipedia, Tire, Components, https://en.wikipedia.org/wiki/Tire : the tread, bead, sidewall, shoulder and ply; circumferential grooves that channel water away and lugs that touch the road; the bead with steel cables that seals against the rim; the sidewall between tread and bead, reinforced with cords, carrying the drive torque and moulded with information; radial body ply cords from bead to bead and belts under the tread. Licence: own work
The drawing: Drawn for this site by script, 2026-09-27. Own work, nothing traced. Licence: own work
How it works
These are the parts of a car tire, a radial tire, the usual kind on cars today, cut across and seated on its wheel's rim. The tread is at the top and the beads at the bottom.
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The outside
The tread meets the road: its lugs grip, and the grooves between them carry water away. At each corner the shoulder turns down into the sidewall, which runs down to the bead that seals against the rim.
Inside the rubber
Steel belts under the tread stiffen it. The casing ply runs from bead to bead and wraps round the bead wires, steel loops that stop the bead stretching off the rim.
The sidewall carries the maker's details and the markings the law requires, moulded into the rubber.
Questions and answers
What are the main parts of a tire?
The tread, the shoulder, the sidewall, the bead and the ply. Inside the rubber are the belts under the tread and the bead wires in each bead.
What is the bead of a tire?
The edge of the tire that sits on the wheel's rim. Steel bead wires inside it keep it from stretching, so it seals the air in and holds the tire on.
What is the difference between radial and bias-ply tires?
In a radial tire the casing ply cords run straight across from bead to bead, with belts under the tread. In a bias-ply tire the plies cross each other at an angle.