Tire Construction

A tire looks simple from the outside — black rubber in a round shape. But inside, a tire is an engineered structure with multiple layers, each doing a specific job. Understanding how a tire is built explains why tires fail, why some ride better than others, and why the markings on the sidewall matter.

Every tire on a modern passenger vehicle is a radial tire. The plies — layers of fabric cords embedded in rubber — run radially, straight across from bead to bead, perpendicular to the direction of travel. Think of the cords running from the left sidewall across the bottom to the right sidewall like the rungs of a ladder. This allows the sidewall to flex independently of the tread. The result is better road contact, cooler running temperatures, and longer tread life. Bias ply tires have plies that run diagonally — at an angle — crossing each other in layers. The sidewall and tread are structurally linked, which makes the tire stiffer and hotter. Bias ply is still used on some trailers and off-road equipment but has been replaced by radial on every passenger vehicle and truck.

Under the tread surface, steel belts wrap around the circumference of the tire. These belts stabilize the tread and keep it flat against the road under load and at speed. Without belts, the tread would distort and squirm under cornering and braking forces. A shifted belt — where one belt layer moves relative to another — causes a vibration or pull that cannot be balanced out. A tire with a shifted belt must be replaced. You can sometimes spot a shifted belt by looking at the tread — one section may appear slightly raised or the tread pattern may look uneven.

Run-flat tires have reinforced sidewalls that can support the vehicle weight even with zero air pressure. The extra-stiff sidewall prevents the tire from collapsing when punctured. Most run-flats allow you to drive 50 miles at up to 50 mph after a complete loss of pressure — enough to reach a service location. The trade-off is a firmer ride because the sidewall is inherently stiffer. Run-flat tires require TPMS because you cannot feel the difference in handling when the tire goes flat — the reinforced sidewall hides the pressure loss. Vehicles designed for run-flats often have no spare tire.

P — passenger vehicle tire. LT would mean light truck, which has a heavier construction. 215 — the section width in millimeters, measured from sidewall to sidewall when mounted and inflated. 65 — the aspect ratio. The sidewall height is 65 percent of the section width. A lower number means a shorter sidewall — a 45 series tire has a much shorter sidewall than a 65, which gives sportier handling but a harsher ride. R — radial construction. 16 — the wheel diameter in inches that this tire fits. After the size you will find numbers and letters like 95H. The 95 is the load index — it corresponds to a specific weight capacity per tire from a standardized chart. The H is the speed rating — the maximum sustained speed the tire is engineered to handle safely.