BASIC TIRE FACTS & DEFINITIONS

Tire Sizes for Lawn & Garden, Industrial, and ATV Tires:

There are three methods to express tire sizes in this category:
1) Overall Diameter x Section Width x Rim Diameter
  • EXAMPLE: 13×6.50-6
  • Referring to the drawing to the left,
    • Nominal Overall Diameter is 13″ (OD)
    • Nominal Section Width is 6.50″ (SW)
    • Rim Diameter is 6″ (BD)
2) Section Width x Section Height x Rim Diameter
  • EXAMPLE: 5.30 / 4.50-6
  • Referring to the drawing to the left,
    • Nominal Section Width is 5.30″ (SW)
    • Nominal Section Height is 4.50″ (SH)
    • Rim Diameter is 6″ (BD)
3) Overall Diameter x Section Width
  • EXAMPLE: 12×1.75
  • Referring to the drawing to the left,
    • Nominal Overall Diameter is 12″ (OD)
    • Nominal Section Width is 1.75″ (SW)

Examples of sizes for various tires in this category:

  • Lawn & Garden (Zero Turn Tire):  24×12-12
  • Lawn & Garden (Wheelbarrow Tire):  4.80/4.00-8
  • ATV Tire:  22×11.00-8
  • Industrial (Handtruck Tire):  4.10/3.50-4
  • General Purpose Solid Wheel:  8×1.75
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Tire Sizes for High-Speed Trailer Tires:

Like Lawn & Garden tires, there is more than one way to express tire sizes in this category:
1) Section Height x Section Width x Rim Diameter
  • EXAMPLE: 4.80x/4.00-8
  • Referring to the drawing to the right,
    • Nominal Section Width is 4.80″ (SW)
    • Nominal Section Height is 4.00″ (SH)
    • Rim Diameter is 8″ (BD)
2) Section Width x Aspect Ratio x Rim Diameter
  • EXAMPLE: ST205/75O14
  • This type of size format is known as “P-Metric”; measurments are metric.
  • ST stands for Special Trailer
  • Referring to the drawing to the right,
    • Nominal Section Width is 205mm (SW)
    • Aspect Ratio is the number appearing immediately
      after the Section Width. It is the relationship of Section
      Height (SH) to Section Width (SW) and is expressed as a percentage – in this case it is 75% of 205mm, or 205/75.(=154mm)
    • D indicates Bias Ply construction. If there was an R shown
      here instead, that would indicate Radial construction.
    • Rim Diameter is 14″ (BD)
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Basic Tire Definitions

Ply Rating
An index of the tires strength; ply rating indicates the maximum recommended load for specific types of service. Ply rating normally does not indicate the number of plies or layers in the tire.
Bead width
The distance between the vertical portions of the rim flange. If the rim is too wide or narrow, the tire will not seat properly. As a rule, bead widths should be ½” to 1 ½” narrower than the section width of the tire to provide for a proper fit.
Section Width
The distance across the tire at its widest part when inflated but not under load.
Section Height
The distance between the top of the tire and the bead seat when the tire is inflated but not under load.
Overall Diameter
The distance from the top to the bottom of the tire when it is inflated but not under load
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