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Knowing some basic facts about tire dimensions and sizes along with a few technical aspects of tire construc-
tion can help clear up much of the confusion many people have in understanding tires and tire sizes. There
are up to 14 parts to a tire, and each one is subjected to different stresses and performance requirements.
About 89% of a tire is rubber compound. The remainder consists of 8% ply and belt materials, and 2.5% steel
wire used in the bead. Understanding the sizing of tires can be especially confusing. There are two popular
methods of identifying lawn and garden tires. The first is overall diameter x section width x rim diameter. An
example of a popular tire using these dimensions is a 16 x 650-8 tire.
The second popular method of designating tire sizes icludes section width x section height x rim diameter, for
example 4.10/3.50-4.
The section width and section height are also used to size car passenger tires. For instance, a P205/75R14 tire
size is explained this way: the P stands for passenger car tire; the 205 is the section width in millimeters;
the 75 indicates the section height to section width ratio (%); the R stands for radial construction;
and the 14 is the rim diameter in inches.
DEFINITIONS:
•
Bead - The inner portion of the tire which fits onto the rim and contains bands of wire to which tire plies
are attached.
•
Ply Rating - Index of tire strength; indicates maximum recommended load for specific types of service.
Usually does not indicate actual number of cord plies in the tire as it did in the past.
•
Rim Diameter - The distance between the vertical portion of the rim flange. If the rim is too wide or too
narrow the tire beads will not seat properly. As a general rule, the proper rim width for a tire will be 1
⁄
2 to
1 1
⁄
2 inches narrower than the section width of the tire, depending on the size of the tire.
•
Section Width - The distance across a tire at its widest part when inflated but not under load (does not
include protective bars or decorations).
•
Section Height - The distance between tread crown and bead seat when tire is inflated but not under load.
•
Tire & Rim Association - An organization of manufacturers which develops standards for rim and tire
dimensions, loads and inflation pressures.
The Tire & Rim Association has set an acceptable variance of 8% from their published dimensions for tire size
designations. Because of this variance it is always prudent to be aware of the possibility of tread and dimen-
sional differences when replacing tires. This becomes especially important when replacing tires on equipment
where tire dimensions are critical to equipment performance.
OVERALL
WIDTH
SECTION
HEIGHT
(D)
SECTION
WIDTH
(B) NOMINAL
RIM
DIAMETER
(C)
OVERALL
DIAMETER
(A)
*Tire and rim association rules allow 8%
variations in dimensions.
Size Typical Use
(A) (B) (D) Lawnmowers
16 x 6.50 - 8*
(A) (B) (D) Industrial,
410/350 - 4 Go Karts
(A) (B) High Wheel Mowers,
16 x 2.125 Bicycles
(B) (C) Motorcycle
400 x 17*
(B) (C) Moped
2
1
⁄
4 x 16
(A) (B) (D) Trailer
16.5 x 6.5 - 8
TIRE & TUBE SECTION
