Lesson 3/Learning Event 2
Combat tires have the same basic construction as standard tires. However, combat tires
are built to operate without air pressure for a limited distance in an emergency. They
should be operated without air pressure only in combat when the tactical situation
requires it. A combat tire is of much heavier construction than a standard tire. It has
more rigid (stiffer) sidewalls, and its heavily cushioned plies are spaced wider apart. On
the inside there is a heavy section of rubber. A beadlock fits between the beads to hold
the tire in place when it is operated without air pressure. These tires are marked with the
word "combat" on the serial-number side of the tire.
Markings on the sidewalls of tires give the manufacturer's name and information that is
important to their use. The first figure is the tire's approximate width in inches when it
is properly mounted. This measurement is taken with the specified amount of air
pressure in the tire when not supporting the vehicle weight. The second number is the
inside diameter of the bead in inches. The third part is the number of plies of cord
fabric. (If this number is shown as 8PR (eight-ply rating), it means the tire is as strong as
a standard eight-ply tire. However, the tire actually contains a lesser number of plies.)
On some of the smaller tires there is a small round mark, about one-quarter of an inch
across, on the sidewall near the bead. This is a balance mark. When the tire is
assembled on the wheel, the mark should be aligned with the valve of the tube.
Both standard and combat tires have serial numbers. Each tire is assigned a different
serial number for identification. Serial numbers are always indented figures in the
sidewall of the tire. Raised figures are made by the tire mold and are not the serial
number.
The inner tube is a doughnut-shaped rubber container that fits inside the tire. It holds
the air that supports the vehicle. The tube can hold only a few pounds of air pressure
when not in the tire; however, the tube will hold very high pressures when enclosed in
the tire.
Because tubes are made of soft rubber, they are easily chafed, pinched, punctured, or
otherwise damaged. Most tubes are made of synthetic, butyl rubber, which holds air
better than natural rubber.
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