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Tyre Nomenclature


Tyre Size Designation


Tyre Dimensions – Definitions

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Overall Diameter (OD):
Inflated diameter of the tyre under reference tyre pressure, mounted on its recommended rim.

Overall Width (OW):
Inflated width of the tyre under reference tyre pressure - including elevations due to lettering, decorations and protective ribs.

Section Width (SW):
Inflated width of the tyre under reference tyre pressure - excluding elevations due to lettering, decorations and protective ribs.

Section Height (SH):
The distance from the bead seat to the outer tread contour of the inflated tyre at center line.

Overall tyre diameter - Nominal Rim Diameter

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Tread Width (TW):
The distance between the extreme edges of the tread, as measured at the surface of the tread.

Aspect Ratio (AR):
The ratio of a tyre's section height (H) to its section width (W) in percentage.

Aspect Ratio (AR)  =

Section Height ( SH ) X 100

Section Width ( SW )


Rim Width (RW):
The liner distance between the flanges of the rim.

Rim Diameter (RD):
Nominal outer diameter of bead seat area of the rim. (It is a size code figure for reference purpose only)

Static Loaded Radius (SLR):
It is the minimum radius acquired by the tyre under reference load and pressure at static condition.

Rolling Circumference (RC):
The distance covered by one revolution of the tyre ( in mm ). The rolling circumference of a tyre is important for establishing the correct tyre slippage.

Tyre Type Nomenclature
• Conventional: The cross – section shape of the tyre has an aspect ratio ( ratio of section height to section width) in the   rage of 0.95 Conventional tires are also referred to as narrow base tires. tires of size designation such as 18.00-25 ,
  24.00-35 ; 24.00-49 etc belong to this category.
• Wide Base: The cross – section shape of this tyre has an aspect ratio in the range of 0.83. Tyre size designations
  such as 20.5-25; 23.5-25; 26.5-29 etc belongs to this category.

Design Tread – Depth
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Off-The-Road Tyre Code Nomenclature And Type Of Service (OTR tires)