to the manufacturer’s recommendations for thespecified operating condition; that is, ideal, moderate,or severe.IDEAL CONDITION.— An ideal condition iswhen a truck is operated over improved, level roads,such as asphalt or concrete, at constant, relativelymoderate speeds with no adverse weather or roadconditions. Under these conditions, recommendedpayload equals 100 percent of maximum permissiblepayload.MODERATE CONDITION.— A moderate con-dition is when a truck is operated at high speeds overimproved highways, such as asphalt or concrete, with orwithout long or steep grades. Moderate conditions alsoinclude operating at moderate speeds over semi-improved roads with gravel or equivalent surfacing, ingently rolling country with few steep grades and noadverse weather or road conditions. Under theseconditions, recommended payload equals 80 percent ofmaximum permissible payload.SEVERE CONDITION.— A severe condition iswhen the vehicle is operated off the highway on roughor hilly terrain or over unimproved or pioneer accessroads with deep ruts, holes, or steep grades. Theseconditions also include operating where traffic hascreated deep holes or ruts in heavy snow, coveringnormally good city streets or highways. Under theseconditions, the recommended payload equals 64 percentof the maximum permissible payload.Weight DistributionDistribution of cargo has a definite bearing on thelife of tires, axles, frame, and other parts of the vehicle.The fact that a truck or trailer is not loaded beyond itsgross vehicle weight capacity does not mean that theindividual tires and axles may not be overloaded byfaulty distribution of the cargo. Additionally, states havemaximums for GVW, GCW, and axle weights. Axleweights prevent the overloading of bridges androadways. Some examples of proper and improperplacement of the load are shown in figure 7-28.To load a truck or tractor-trailer properly, you haveto determine the center of the payload. In a truck, theposition of the center of the payload is the center of thebody or the point midway between the rear of thedriver’s cab and the tailgate. In a tractor-trailer unit, theposition of the center of the payload is roughly the centerof the trailer body, because the front wheels of the tractorseldom carry any of the payload. When you are loading,ensure that the maximum capacity of the vehicle is not7-25Figure 7-29.—Distribution of weight.exceeded over any one axle and, if possible, that loadsare distributed so there is less-than-maximum axleloading. Examples of approximate distribution of totalweight are shown in figure 7-29.The payload weight must be distributed over thebody properly so the percentage of weight carried by thefront axle and that carried by the rear axle equals theratio for which the vehicle was designed, as shown infigure 7-29.Loading CargoThe tractor-trailer can be adapted to transportvarious types of materials, such as fragile, bulky,compact, dense, rough and high center-of-gravity items.To accommodate a variety of items, you must plan theload, properly prepare the tractor-trailer, and secure theload to the vehicle. Securing the load by restraining itwith proper lines, cargo straps, chains, or fastened bytie-downs or binders should keep it from shifting orfalling off the vehicle. Should a load fall from a vehicle,it could foul underpasses, culverts, bridge abutments,and create a hazard to pedestrians. Protect fragile items
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