Modern Tire Dealer

DEC 2018

Magazine for the professional tire industry

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A G T i r e T a l k M T D D e c e m b e r 2 0 1 8 74 or per axle, like on a grain elevator scale. An incorrect weight distribution can create issues like "power hop," where the front axle is too "light" (losing traction) and the rear axle is overloaded, creating excessive "grip." 3. e third point is tire inflation pres- sure. Each tire's size load capacity changes with inflation pressure changes -- the higher the inflation pressure (more air volume in the tire chamber) the higher the load capacity. is load capacity is defined by the type of tire (bias, radial, IF, VF, IMP, etc.) and design (width, rim diameter and ratio), and is regulated by the TRA (Tire and Rim Association) in the U.S. or the ETRTO (European Tire and Rim Technical Organization) in Europe. A note related to minimum pressure: Even if the load is low enough to allow for very low inflation pressure (below 10 psi), the minimum inflation pressure should not be below the 10-12 psi mark. Below this pressure value is risk of rim-to-tire slippageā€¦ as there is less pressure from the tire bead against the rim flange, reducing the efficiency of power transmission from the tractor to the tire. Scott Sloan : ag product manager/global LSW, Titan International Inc.: Whether running in heavy tillage or moving heavy hay bales, the correct ballast is important. Fact is, too much weight can cause a trac- tor to feel sluggish, increase soil compaction, reduce fuel efficiency and result in premature drivetrain wear. Too little weight can result in tire slippage, reduce fuel efficiency and cause premature tire tread wear. e end game is trying to minimize tire slippage when you head to the field. Most manufacturers shoot for slip in the 8% to 15% range. Anything over that is extremely noticeable and not very efficient. Growers feel they are sending a lot of money with little return through the exhaust stack. Most growers I deal with do prefer to be running in the 3% to 9% range. So a quick, fast approach to get in the ballpark for example on a 4WD depending on the application to have anywhere from 85 lbs. to 125 lbs. per rated horsepower. For instance, a 4WD rated at 500 hp should be in the 50K to 55K total weight with 55%-60% on the front and 40%-45% on the rear. Not only is the total machine weight important, the distribution of that weight is just as critical (see Table 1 below for a quick reference to proper ballasting and weight distributions). At the end of the day, each grower needs to understand the factors involved and the objective for their individual operation. One end user may be okay with a little more slip and a lighter machine, while the other wants to pin all the power to the ground. Jim Enyart , technical manager, CEAT Specialty Tires Inc.: Ballasting has been utilized for equipment functionality and stability as well as transferring power to the ground. Many types of ballasting materials have been utilized, including rocks, soil, cast iron, water, calcium chloride, magnesium chloride, beet juice and more. e choice of ballasting materials includes many fac - tors, but the most critical aspect of adding ballasting is how much weight to add and where to place these materials. e first critical factor is knowing the engine horsepower of the tractor and the axle weights. Ideally, the weight per horse- power ratio should be between 100 and 120 pounds/hp. e lighter weights are more desirable and efficient as long as there are no performance issues such as stability or wheel hop. Increased weight ratios may be utilized to reduce slip, which increases efficiency, especially in demanding applications. For 2-wheel drive tractors the weight distribution should be 30% on the front axle and 70% on the rear . MFWD tractors should have 35% on the front and 65% on the rear axle. Four-wheel drive tractors should carry 60% on the front and 40% on the rear axle. Allowances for additional weight due to attachments should also be calculated into your weight distribution adjustments. Air pressures should be set just above the maximum load carrying capacity you are expecting from your tires based on the most demanding application. Changing air pressures between road and field usage is time consuming and not practiced. Air pres- sures should be set for the road application due to the higher speeds, which is the most demanding from a load carrying aspect. Bradley Harris , manager, global agricultural field engineering, Firestone Ag Division, Bridgestone Americas Tire Operations LLC: To get the most efficiency from a tractor, it's critical to have the proper amount of ballast and the weight appropri- ately split between the front and rear axle. ere are some general rules that tractor and tire manufacturers use when helping customers set up tractors used for fieldwork. Step One: Identify the horsepower rating of the tractor. For 2WD and mechanical front-wheel drive (MFWD) tractors, the rated PTO horsepower is used. For 4WD tractors, the tractor's rated engine horsepower is used. For the following calculations, we will use a MFWD tractor with 180 PTO horsepower being used to pull drawbar implements as the example. Step Two: Calculate the target total tractor weight. Example target tractor weight: 180 PTO HP x 130 lbs./PTO HP = 23,400 lbs. (see Chart 1). CHART 1: WEIGHT PER HORSEPOWER RECOMMENDATIONS Tractor Type Target Tractor Weight 2WD 145 LBS/PTO HP MFWD 130 LBS/PTO HP 4WD 110 LBS/Engine HP Weight per horsepower recommenda- tions for the three types of tractors. SOURCE: BRIDGESTONE AMERICAS TIRE OPERATIONS Total tractor weight Percent on front axle 4WD 85-125 pounds per engine horsepower. For towed implements, use 51-55%. This is very important to help in control of power hop. With no hitch, PTO or ballast, the front will be 60% or more out of the factory. For hitch-mounted implements, use 55-60%. For towed implements with very high downward loads on drawbars, use 55-65%. MFWD 120-145 pounds per PTO horsepower. 130 is most common. 35-40% for all types of implements. Power hop is easier to control as front split is reduced. 2WD row crop Same as MFWD. 25-35%. Use higher percentage with heavy hitch- mounted implements. TABLE 1: PROPER BALLASTING AND WEIGHT DISTRIBUTION, PER TITAN

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