TIRES/WHEELS
Tire Technical Information
Knowing some basic facts about tire dimensions and sizes along with a few technical aspects of tire
construction can help clear up much of the confusion many people have in understanding tire 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 8.5% ply and belt materi-
als, 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 includes section width x section height x rim diam-
eter, 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 mil-
limeters; the "75" indicates the section height to section width ratio (%); the "R" stands for radial construc-
tion; and the "14" is the rim diameter in inches.
Some definitions:
Bead: The inner portion of the tire which fits on 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 head 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
dimensional differences when replacing tires. This becomes especially important when replacing tires on
equipment where tire dimensions are critical to equipment performance.
SIZE
TYPICAL USE
(A) (B) (C)
16 X 6.50 -8*
Lawn mowers
(B) (D) (C)
410/350-4
Industrial; Go Karts
(A) (B)
High Wheel Mowers
16 x 2.125
Bicycles
(B) (C)
400 - 17*
Motorcycle
(B) (C)
2 1/4 - 16
Moped
(A) (B) (C)
16.5 x 6.5 x 8
Trailer
* Tire and rim association rules allow 8% variations in dimensions
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