safe operation on wet and dry roads. This tread is oftenused on modern highway-operated tires.Rock Service TreadRock service treads (fig. 3-23) are characterized bynarrow voids between lugs so that loose rock cannot becaught and tear the tread lugs loose from the tire body.This nondirectional tread design is used on tires forservice on rough terrain.in either park, first, or reverse, depending on the type oftransmission. Locate something suitable for blockingthe wheels to prevent the vehicle from rolling as youraise it with the jack. Never block the wheels on the axleyou are raising with the jack.For automobiles and light trucks, remove thehubcap, if so equipped, by using the lug wrench or asuitable substitute. Then slightly loosen the bolts or nutsthat hold the wheel to the hub. Next, raise the wheel withthe jack and observe the vehicle to ensure that it doesnot 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 sinkinto the ground from the weight of the vehicle. If thejack shows signs of sinking, move the vehicle to a morestable surface or place a plank of solid wood or steelmatting under the jack to spread out the ground-bearingpressure. After the wheel has cleared the groundapproximately 1 inch, finish removing the lug nuts orbolts and remove the wheel from the vehicle.Earthmover TreadThe earthmover tread design (fig. 3-24) is for tiresused on heavy equipment working in areas, such as aborrow pit or off-road service.TIRE REMOVALBefore removing a tire from a vehicle, ensure theemergency brake is locked and the transmission lever isCAUTIONFigure 3-23.—Rock service tread.Figure 3-24.—Earthmover tread.Do not leave the vehicle suspended on thejack. If work is to be performed on the vehiclewhile the tire is removed, place an approvedsafety stand or suitable blocks under the axle tosupport the vehicle. If no work is to beperformed, install the spare tire as soon aspossible to prevent damage to the vehicle orpersonnel.On large vehicles with dual-disc wheels, both discsare fastened together by two nuts on each hub bolt, oneFigure 3-25.-Dual-disc wheel mounting.3-12
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