Understanding OTR Terminology

Off-the-road (OTR) tires are tough, but for those who don’t know a lot about OTR tires, understanding the terminology used to describe them is just as tough.

Understanding OTR TerminologyWhile there are many different types of OTR tires, and a wide variety of tread patterns depending on the exact application the tires will be used for, there is some basic OTR tire terminology that helps describe the basic makeup of OTR tires.

Typically earthmoving and other OTR tires are composite products that are manufactured from steel, rubber compounds, and other synthetic or textile reinforcements. The terminology below refers to a tubeless, radial ply tire with a steel carcass.

Basic Terminology for OTR Tires

Imagine a tubeless tire cut away into sections. On the outside is the tread, and on the inside, the chafer. In between there are a number of layers each of which has its own function.

  • Tread is the outside layer of OTR tires that primarily provides traction, but also protects the carcass of the tire below. This is the part of the tire that comes into direct contact with the road or gravel surface OTR vehicles or equipment travel on. Additonally:
    • Tread groove is the space between rows of tread.
    • Tread depth is the measurement from the surface of the tread to the bottom of tread grooves.
    • Tread design refers to the pattern formed by the tread grooves and other tread elements.
    • Tread pattern is the term used to describe the overall structure of the tire tread.
    • Tread lugs and tread voids form part of the tread pattern. The lugs come into contact with the road or other terrain, while the voids are the spaces between the lugs.
  • Carcass is another word for the tire casing and refers to the main body of OTR tires that consists of body plies and wire beads. It doesn’t include the tread of the tire or its sidewall.
  • Belt package is comprised of a number of low-angle, steel cord layers that provide the tire with strength. This layer also stabilizes OTR tires and prevents any form of penetration into the carcass of the tire.
  • Radial ply is that part of the tire that transmits load, steering and braking forces between the road and the wheel. It also withstands burst loads of OTR tires when they are subjected to operating pressure. The ply may comprise one or two layers that are impact and heat resistant.
    • Ply rating or load range are the terms used to describe the carrying capacity of tires in relation to the vehicle.
  • Inner liner is a compounded rubber layer specifically found in tubeless tires. It prevents loss of air from the tire and in this way maintains air pressure in the tire.
  • Sidewall is found at the sides of OTR tires. This layer covers everything but the tread and belt package, protecting the ply and helping to withstand weathering and flexing.
    • Sidewall strength refers to the resistance of OTR tires to tears and punctures in the sides of the tires. Tires with greater sidewall strength will be more resistant to flex, even when the tire has been aired down to a relatively low pressure.
  • Bead bundle refers to a steel rim of sorts that sits outside the sidewall, and seats the tire. It also seals the tire on the rim and effectively maintains its position.
  • Apex is found over the bead bundle in the form of rubber filler in the bead and lower part of the sidewall. Its function is to provide progressive transition from the bead bundle zone – which is stiff – to the flexible rubber tire wall.
  • Chafer takes the form of a hard rubber layer that is able to resist erosion of the bead area by the rim flange.

If you would like to know more about OTR tires, or want to purchase the right type for your vehicles and OTR equipment, contact OTR Tires Worldwide.