Lancas, Kleber P. : K.P. Lancas is Visiting Scholar, Department of Biological and Agricultural Engineering, UC Davis.

Shafii, Sayedahmad : S. Shafii is Visiting Scholar, Department of Biological and Agricultural Engineering, UC Davis.

Sime, Muluneh : M. Sime is Research Assistant, Department of Biological and Agricultural Engineering, UC Davis.

Upadhyaya, Shrini K. : S.K. Upadhyaya is Professor, Department of Biological and Agricultural Engineering, UC Davis.

Overinflated tractor tires waste fuel , reduce productivity Kleber P . Lancas o Shrini K . Upadhyaya o Muluneh Sime P SayedahmadShafii Under typical California farming tion will grow , leading to severe oscil - clay soil . The summer tests were con - conditions , field experiments have lation . In an effort to solve this prob - ducted on the Russell ranch in Davis , lem , engineers have found that power shown that using a low / correct in - in a field with dry , Rincon silt clay / hop can be controlled if radial ply tires flationpressure for radial ply tires Yo10 silt loam soil . This field had been are operated at much lower pressures , stubble - disked following a winter can result in significant savings which are chosen based on axle load . wheat crop . Field operations consid - in time and money . It can also This pressure level is referred to as ered during this study were stubble lessen soil compactionand help â?쳌 low / correct pressure . â?쳌 Working disking in the spring and subsoiling control power - hop in mechanical closely with tire manufacturers , engi - with a mounted subsoiler in the front - wheel drive and four - wheel neers at tractor manufacturing compa - summer . drive tractors . In tilled , moist nies developed a new set of guidelines Spring tests examined two different Capay clay soil , the tractor using to select low / correct pressures for ra - soil conditions ( tilledand untilled ) low / correct tire pressure required dial ply tractor tires . Use of these low / and two tractor tire - inflation pres - 20 % less diesel fuel and produc - correct pressures turns out to be bene - sures . We selected four rice checks of 5.7 % during the tivity increased ficial not only in controllingpower - about 13 acres each . Two checks were same stubble - disking operation . hop , but also for higher tractive disked , using a finishing disk , to cre - ( implement - pullingability ) and fuel ate tilled conditions.One of these It has long been recognized that radial efficiencies , enhanced productivity tilled checks , and one untilled check , ply tires perform better than bias ply and a reduction in the extent of soil then were randomly assigned to a tires at the same axle load because of a compaction . This win - win situation high inflationpressure of 24 psi . The belt - stiffening effect , which reduces has led to considerableinterest nation - remaining checks were assigned low / lug deflection.Radial ply tires also wide in the use of low / correct pres - correct pressure treatments of 13 psi in lead to increased tire deflection , which sures for radial ply tractor tires . front axle tires and 11psi in rear axle increases soil - tirecontact area , and The objective of this study was to tires . Checks assigned the low / correct hence their pulling ability.However , quantify the benefits of employing pressure treatment were disked using use of radial ply tires with mechanical low / correct pressures on radial ply an 18 - footKewanee stubble disk . Fuel front - wheeldrive ( MFWD ) and four - tractor tires under typical California consumption in each check was mea - wheel drive ( 4WD ) tractors also can farming conditions . sured using a simple fuel gauge de - contribute to a vibration problem signed for this study . Initial fuel level Field experiments known as â?? power hop , â?쳌 which occurs was noted by parking the tractor in a when operating towed implements at We conducted two tests during the specificlocation before a test . After the moderate to high loads . spring and summer of 1994 , using a test , the tractor was parked in the Power - hop , also called â?? wheel - 350 hp John Deere 8870,4WD tractor , same location and refueled to the ini - hop , â?쳌 â?? tire - hop , â?쳌 or â?쳌 tractor - hop , â?쳌 is a which was equipped with 20.8R48 tial level . Fuel consumption was deter - combination of bounce and pitch vi - duals on both front and rear axles . mined as the amount of fuel necessary bration . If no corrective action is taken Tests were conducted in the spring in to refill . Productivity was determined ( such as reducing power ) , the vibra - Woodland , in a relatively wet Capay by measuring the time it took to disk 28 CALIFORNIA AGRICULTURE , VOLUME 50 , NUMBER 2 tent , and texture . Al - though no direct re - lationship exists be - tween compactness and cone index , it is often used as a rela - tive indicator of soil compaction . Cone index values were replicated 10times in each check . In ad - dition , eight cone in - dex values were measured in the tire track and six in the undisturbed area in the vicinity of tire tracks ( fig . 1 ) . Instan - taneous values of slip , forward speed and engine rpm were measured us - ing a performance monitor installed in the tractor cab . The summer tests were conducted with a mounted , 9 - shank John Deere subsoiler using two inflation pressure levels of 24 psi and low / correct pressure ( 13psi on the front axle and 14 psi on the rear axle ) . The field was di - vided into two Use of iowlcorrecttire pressure ( fop and lower re # ) controls power - hop and improves blocks , which were implement - pullingability and fuel efficiencies , while enhancing productivityand reduc - further subdivided into two 1,500 - ing soil compaction . Overinflatedtires shown In top and lower right . foot - by - 250 - footplots . These plots This is essentially a measure of how were randomly assigned an inflation 1,000 feet along a straight line ; we hard or compact the soil is with depth . pressure level . The test procedure was measured this 10times in each check . Cone index is a compositesoil param - similar to that employed in the spring . To determine soil moisture content eter that depends on soil density ( mea - Experimental data consisted of fuel and bulk density , we obtained five soil sure of soil compaction ) , moisture con - consumption , time to travel 1,000 feet samples from each check using a volu - during the field operation , moisture content , bulk density , cone index data Tire tracks ( under the track and adjacent to the 7 track in the undisturbed area ) , and standard cone penetrometer is a cone tractor performancedata such as slip , with a base diameter of 0.798 inches forward speed and engine rpm . and an apex angle of 30 degrees 0 " I 11 Selection of low / correct pressure Cone index measurement sites1 Since the spring tests were con - pushed into the soil at the rate of 72 A . On track ( 8 replications ) 6 . On track ( 6 replicetions ) ducted with a towed disk harrow , the inches per minute . The forcerequired static weight distribution of the prop - to push this probe through the soil di - erly ballasted tractor was necessary to vided by the base area of 0.5 square determine the low / Fig . 1 . Cone index measurement sites . correct pressure . inches is known as the cone index . CALIFORNIA AGRICULTURE , MARCH - APRIL 1996 29 This information can be obtained from the tractor dealer . For our tractor , weight distribution was 21,030 pounds on the front axle and 18,330pounds on the rear axle . Load per tire on the front axle was 5,257.5pounds and 4,582.5 pounds on the rear axle . The correct inflation pressures for 20.8R42 tires used as duals were 13psi in front axle tires and 11psi in rear axle tires . The summer tests were conducted with a mounted subsoiler . When a mounted implement is used , the rear axle must be weighed with the imple - ment in raised position because tire wear during transport on paved roads becomes the limiting condition for tractors with mounted implements . This weight can be determined easily with the help of a truck scale . In our case , the rear axle weight was 22,690 pounds . Note that the front axle is weighed with the implement lowered or detached , which is the same as the static weight . This weight can be ob - tained from the tractor dealer or by weighing with the implement low - ered . The load per tire and correct in - flation pressure for tires on the rear axle , in our case , were 5,672.5 pounds and 14psi , respectively.Front tire pressure was 13psi , as in the spring tests . Fuel savings , higher productivity The soil at both test locations was quite moist in spring ( average of 37.2 % on dry basis ) and relatively dry in summer ( average of 10.2 % on dry ba - sis ) ( table 1 ) . The specific gravity of the soil in the rice checks was lower than that of summer plots because the clay soil swelled considerably at high mois - ture content . Tables 2 and 3 list mean values of fuel consumption rate , productivity , cone index values under the tire tracks ( on - track ) and adjacent to the tire tracks ( off - track ) , and engine perfor - mance data ( instantaneous engine rpm , forward speed and wheel slip ) . These data indicate that using low / correct tire pressure reduced fuel con - sumption , increased productivity ( ac / hour ) , and led to higher forward speed and lower slip values in all three cases - tilled and untilled dur - 30 CALIFORNIA AGRICULTURE , VOLUME 50 , NUMBER 2 Fig . 2 . Comparisonof soil compaction Fig . 3 . Comparisonof soil compaction Fig . 4 . Comparisonof soil compaction ( cone index values ) for lowlcorrect and ( cone index values ) for low / correct and ( cone index values ) increase , in percent - high inflation pressure ( 24 psi ) tires , in high inflation pressure ( 24 psi ) tires , in age , for lowlcorrectand high inflation tilled layer , for the summer test . untilled layer , for the summer test . pressure ( 24 psi ) tires , in tilled and untilled layers , for the summer test . ing the spring , and stubble - disked in cone index values with the low / cor - 2 . In tilled , moist ( 37.2 % moisture the summer . The increase in produc - rect pressure treatment . Plots that re - content on dry basis ) Capay clay soil , tivity and forward speed , and the de - ceived 24 psi pressure treatment the tractor required 20 % less diesel crease in wheel slip go hand - in - hand showed a 25 % increase . Cone index fuel and productivity increased 5.7 % values obtained in tilled and untilled since they are mathematically re - during the same stubble - disking op - lated . layers during summer tests indicate eration . However , the changes in cone using low / index values were about the same for Based on the savings in fuel con - correct pressure reduces both the high pressure and low / sumption and enhancement in pro - the extent of soil compaction when cor - ductivity ( table 4 ) , we estimated sav - compared to using high inflation pres - rect pressure treatments . ings of $ 791 / section in tomato sure ( figs . 2 and 3 ) . In the tilled , wet 3 . Fuel savings were estimated at production , $ 468 / section in rice pro - Capay clay soil , changes in cone index 6 % and increase in productivity at duction , and $ 59l / section in cotton values were similar for both pressure 4.6 % when the tractor was used for production . Total potential savings in treatments in the upper tilled and the subsoiling previously stubble - disked , Californiafor production of these lower untilled layers ( fig . 4 ) . However , dry Rincon silt clay / Yolo silt loam three crops was estimated at 2.3 mil - we believe these cone index values plots with a mounted subsoiler . Mean lion gallons of diesel fuel and 60,000 represent the resistance of large , wet increase in cone index values in tire hours of labor . At $ 0.71 per gallon of clay lumps created by the previous tracks was 119.4 % for high pressure diesel fuel , savings in fuel and produc - disking operation . Under such condi - treatments compared to 23.4 % for tivity were estimated at about $ 2 mil - tions , it is very difficult , if not impos - low / correct pressure treatment . lion . These estimates were based on sible , to get representative cone index typical primary tillage operations em - data . It should also be noted that there K.P . Lancas is Visiting Scholar , S.K . ployed in the production of these three was no incidence of power - hop during Upadhyaya is Professor , M . Sime is Re - crops . search Assistant , and the spring or summer tests . S . Shafii is Visiting Scholar , Department of Biological and Ag - Soil compaction Summary of benefits ricultural Engineering , UC Davis . The differencesin soil compaction The authors are grateful to the Califor - Our data was obtained by using a levels depended on existing soil condi - nia Energy Commissionfor theirfinaizcial JohnDeere 8870,4WD tractor tions during field tests . The extent of support for this project . Moreover , we are equipped with 20.81342 duals on both soil compaction - as measured by indebted to Dr . Jack Wiley , Principal En - the front and rear axle . Based on our mean cone index values - increased gineer , Deere and Co . , and Mr . Drew study , we found that use of low / cor - in the untilled , moist Capay clay soil Shorter , Agricultural Tire Engineer , The rect pressure for radial ply tractor tires by 9.8 % when low / correct pressure Goodyear Tire and Rubber Co . , for many compared to a high inflation pressures was employed and 70.3 % when 24 psi valuable suggestions during the course of of 24 psi led to the following : this project . inflation pressure was employed 1 . The tractor consumed 18.3 % less For additional information on how to ( tables2 and 3 ) . In the relatively dry , diesel fuel while its productivity in - stubble - disked , Rincon silt clay / Yo10 determine lowlcorrect tire inflation pres - creased by 7.5 % when stubble disking silt loam soil , soil compaction in - sure , refer to in an undisturbed , moist ( 37.2 % mois - a handbook entitled â?? How to get the mostfrom radial ply tractor tires : creased by 23.4 % when low / ture content on dry basis ) Capay clay correct soil . The increase in mean cone index pressure was employed and by 119.4 % A guide to select the correct inflation pres - when 24 psi pressure was utilized . In sure . values in the tire tracks was higher at â?쳌 The handbook is available through the Biological and Agricultural Engineer - 24 psi pressure ( 70.3 % ) than when the hard soil below the tilled layer , which was measured to a depth of 12 low / correct pressure was used ( only ing Department , UC , Davis , CA 95616 , inches , there was almost no change in 9.87â??0 ) . ( 916 ) 752 - 0102 . CALIFORNIA AGRICULTURE , MARCH - APRIL 1996 31