safe operation on wet and dry roads. This tread is often
used on modern highway-operated tires.
Rock Service Tread
Rock service treads (fig. 3-23) are characterized by
narrow voids between lugs so that loose rock cannot be
caught and tear the tread lugs loose from the tire body.
This nondirectional tread design is used on tires for
service on rough terrain.
in either park, first, or reverse, depending on the type of
transmission. Locate something suitable for blocking
the wheels to prevent the vehicle from rolling as you
raise it with the jack. Never block the wheels on the axle
you are raising with the jack.
For automobiles and light trucks, remove the
hubcap, if so equipped, by using the lug wrench or a
suitable substitute. Then slightly loosen the bolts or nuts
that hold the wheel to the hub. Next, raise the wheel with
the jack and observe the vehicle to ensure that it does
not roll while being raised. If the vehicle starts to roll,
lower the jack and add additional blocking to the wheels.
Also, observe the jack and ensure that it does not sink
into the ground from the weight of the vehicle. If the
jack shows signs of sinking, move the vehicle to a more
stable surface or place a plank of solid wood or steel
matting under the jack to spread out the ground-bearing
pressure. After the wheel has cleared the ground
approximately 1 inch, finish removing the lug nuts or
bolts and remove the wheel from the vehicle.
Earthmover Tread
The earthmover tread design (fig. 3-24) is for tires
used on heavy equipment working in areas, such as a
borrow pit or off-road service.
TIRE REMOVAL
Before removing a tire from a vehicle, ensure the
emergency brake is locked and the transmission lever is
CAUTION
Figure 3-23.—Rock service tread.
Figure 3-24.—Earthmover tread.
Do not leave the vehicle suspended on the
jack. If work is to be performed on the vehicle
while the tire is removed, place an approved
safety stand or suitable blocks under the axle to
support the vehicle. If no work is to be
performed, install the spare tire as soon as
possible to prevent damage to the vehicle or
personnel.
On large vehicles with dual-disc wheels, both discs
are fastened together by two nuts on each hub bolt, one
Figure 3-25.-Dual-disc wheel mounting.
3-12
