Humphreys Hitch and Trailer Parts

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Definitions for terms used to define trailer tires.
Design Rim Width: The specific rim width assigned to each tire size designation, to determine basic tire dimensions.
Section Width: The maximum width of a new tire.
Overall Diameter: The diameter of an inflated tire at the outer most surface of the tread.
Maximum Load Capacity: The maximum weight a tire is designed to carry, under standard use conditions.
Tire Terms
Load Identification:
Load Range identified with a letter (A, B, C, etc.) Standard Load and Extra Load: Used to identify a given size tire with its load and inflation limits, when used in a specific type of service.
Ply Rating is a term used to identify a given tire with its maximum recommended load, when used in a specific type of service. It is an index of tire strength and does not necessarily represent the number of cord plied in the tire.
Static Load Radius is the dimensions from the bottom of the tire to the center line of an axle, when the tire is loaded at its rated capacity.
How The Tire Part Number System Works: Part numbers incorporate tire sizes and descriptions, to allow you to easily determine the tires you need to order. For example, part numbers 7516BE and ST205-75-R15BC-I can be interpreted as follows:
  • For 7516BE:
  • 7526 = 7.50 X 16
  • B = Blackwall
  • E = Load Range E
    • For ST205-75-R15BC-I:
    • ST205-75-R15 = ST205-17-15 Radial
    • B = Blackwall
    • C = Load Range C