Tractive characteristics of radial ply and bias ply tyres in a California soil

Four tyres (18.4-38, 18.4R38, 14.9-28, 14.9R28) were tested using the UCD single wheel traction tester. Each tyre was tested at two different inflation pressures and three different vertical loads at each inflation pressure. All tests were conducted in a well tilled Yolo loam soil. A dimensional analysis procedure was used to design and analyse the experiment. Two models were considered: (A) using inflation pressure as a variable, and (B) using tyre deflection as a variable. The effect of tyre type, tyre size, tyre inflation pressure and dynamic load on (1) net traction ratio at 20% slip and (2) average tractive efficiency in the 0–30% slip range were investigated using an ANOVA technique. An estimate of the possible energy savings due to the use of radial ply tyres instead of bias ply tyres in California agriculture was made.     

Soil stress and compaction effects for four tractor tyres

Compaction effects and soil stresses were examined for four tractor tyres under three inflation pressures: 67, 100 and 150% of the recommended pressure. The four tyres were 18.4 R 38, 520/70 R 38, 600/65 R 38 and 650/60-38 and they carried a wheel load of 2590 kg. The 650/60-38 was a bias-ply tyre while the other three were radial tyres. Increased inflation pressure significantly increased all measured parameters: rut depth, penetration resistance and soil stress at 20 and 40 cm depth. The 18.4 R 38 caused a greater rut depth and penetration resistance than the other tyres, which did not differ significantly from each other. The soil stress was highest for the 18.4 R 38, followed by the 650/60-38. The low-profile tyres decreased compaction compared with the 18.4–38 tyre, mainly by allowing a lower inflation pressure. The use of low-profile tyres did not reduce compaction if not used at a lower inflation pressure. The bias-ply tyre caused a higher stress in the soil than the radial tyres when used with the same inflation pressure, but the compaction effects in terms of rut depth and penetration resistance were not greater for this tyre than for the radial low-profile tyres.     

Performance prediction of animal drawn vehicle tyres in sand

Four animal drawn vehicle (ADV) tyres of 5.00–19, 6.00–19, 7.00–19 and 8.00–19 sizes were tested in sand under various but controlled conditions in an indoor soil bin. A tyre test carriage with four-bar parallel linkage was developed for accommodating a single wheel of different sizes. Performance tests were conducted at five levels of inflation pressure and load. The sand compaction level was varied in the range of 3.4–4.5 MPa/m and forward speed of the test carriage was maintained at 3.1 km/h. Performance of the tyres 7.00–19 and 8.00–19 was identical and offered less rolling resistance as compared to other tyres. However, their use in camel carts may not be recommended beyond the payload of 6 kN on single wheel with inflation pressure and sand compaction range of 172–379 kPa and 3.4 –4.5 MPa/m, respectively. Based on the experimental results, empirical models were developed to predict the performance of tyres. The accuracy of prediction of the developed empirical models was compared with that of existing semi-empirical approaches. Model with sand mobility number considered relatively simple and convenient to use in the field and yields reasonably good prediction for rolling resistance and sinkage.     

The performance of free rolling rigid and flexible wheels on sand

Experimental results are presented for a towed 6–16 smooth tyre and the same size rigid steel wheel in three types of sands covering a wide range of particle size distribution, two dry and one submerged sands. Their performance was compared at high and low tyre inflation pressures, two vertical loads and a wide range of soil compaction for each sand. The sand performance prediction number, Ns, proposed by the U.S. Army Engineer Waterways Experiment Station (W.E.S.) was then applied to compare with the measured results for the tyre. It was found that in all the three sands the coefficient of rolling resistance was substantially underestimated by the W.E.S. method. However Ns = 10–20 was found to be very important overall criterion for towed tyres on sand. The correlation between the skid and the fractional sinkage of the rigid wheel and the tyre was also examined.     

Tyre flexibility and mobility on soft soils

Five model tyres were tested in the soil bin to investigate the effects of wheel flexibility on the tyre-soil performances. Two different soil types were used together with various inflation pressures which governed the tyre flexibility. The results confirm that tyre flexibility contributes significantly to the development of all the energy components [equation (1)] in the tyre-soil system. As can be seen from the contrasting performances shown, increasing the inflation pressure may allow for a favourable increase in the drawbar pull in one soil (frictional soil) so long as the input energy available can be increased, whilst the reverse may be true in the case of the other (clay) soil. The finite element model used satisfactorily confirms the measered values obtained and is seen to be able to account for tyre flexibility as shown in Figs. 11–14.     

The deflection and contact characteristics of some agricultural tyres with zero sinkage

The vertical deflection, contact area, and ground pressure of three agricultural tractor rear tyres (11.2–28, 12.4–28, 13.6–28) were investigated at different normal loads and inflation pressures on a firm surface. A linear mathematical model was evolved to establish relationship among different parameters. The model could be used to represent tyre behaviour under varying operational parameters.     

Effect of inflation pressure on motion resistance ratio of a high-lug agricultural tyre

A single wheel tyre facility at University Putra Malaysia (UPM) was used to check the validity of Wismer–Luth and Brixius equations in predicting the motion resistance ratio of a high-lug agricultural tyre and to investigate the effect of inflation pressure. A Bridgestone 5-12, 4 ply, lug M was tested on sandy-clay-loam soil. The experiments were conducted by running the tyre in towing mode. Three inflation pressures (i.e., 166, 193 and 221 kPa) were investigated and wheel numerics ranging between 0 and 70. The analysis of covariance (ANCOVA) revealed that both inflation pressure and wheel numeric have significant effects on tyre motion resistance ratio. Regression analysis was also conducted to determine the closeness of fit for Wismer–Luth’s and Brixius’ equations in predicting the motion resistance ratio of the tested tyre. Finally, three new logarithmic models for tyre motion resistance were formulated. The advantage of reducing tyre inflation pressure from 221 (nominal pressure) to 193 kPa on the motion resistance ratio of the high-lug agricultural tyre was pronounced. However, the tyre’s motion resistance ratio deteriorated with further reduction in tyre inflation pressure from 221 (nominal pressure) to 166 kPa.     

The ability of agricultural tyres to distribute the wheel load at the soil-tyre interface

Bigger tyres with lower inflation pressure at equivalent wheel loads are expected to reduce the stresses transmitted to the soil. We measured the contact area and the vertical stress distribution near the soil-tyre interface for five agricultural implement tyres at 30 and 60 kN wheel load and rated inflation pressures. Seventeen stress transducers were installed at 0.1 m depth in a sandy soil at a water content slightly lower than field capacity and covered with loose soil. The recently developed model FRIDA was successfully fitted to the experimental stress data across the footprint. The contact area reflected the size of the tyres. The small tyres had identical contact area at the two loads, while it increased with load for the two biggest tyres. The small tyres presented uneven stress distributions with high peak stresses. Across the tests, the tyre inflation pressure described well the measured peak stress as well as the modelled maximum stress. The latter seems to be appropriate in evaluating vehicle trafficability. We found significant differences among tyres for the slope of a linear regression between the mean ground pressure and the inflation pressure, while the tyres displayed the same interception on the mean ground pressure axis. Our results therefore suggest that the slope of this relation is the most sensitive expression of tyres’ ability to deflect and transfer stresses to the soil. The two small tyres performed poorer in this respect than the larger tyres. Tests were limited to one soil strength, with future research directed toward a broader spectrum of soil strengths.     

Modelling power requirement for traction tyres with zero sinkage

A model was developed by dimensional analysis to predict the gross traction at zero net traction for traction tyres (11.2–28, 12.4–28, 13.6–28) on a hard surface. Different parameters that affect the torque requirement, namely tyre size, tyre deflection, axle load, and rolling radius, were considered for the analysis. Experiments were conducted to study the effect of various wheel and system parameters on torque and energy consumed per unit distance travelled. The model developed predicts the torque requirement in an acceptable range and can be used as a reference for further traction studies of these tyres in various soils.     

A tyre option for sugarcane haulout trucks to minimise soil compaction

Change in soil cone resistance was used as an indicator of soil compaction after the passage of haulout trucks running dual tyres or super single tyres. Cone resistance was measured to a depth of 0.6 m in the inter-row and in transects from the middle of one crop row to the middle of the adjacent row. Treatments consisted of one, two, three and four passes by both dual tyres and super single tyres and one and two passes of reduced pressure and standard pressure super single tyres aligned down the inter-row. Soil cone resistance increased with an increasing number of passes under the dual tyres. There was less change in soil cone resistance after the passage of super single tyres. A small reduction in soil cone resistance resulted when low tyre pressure was used compared with the standard tyre pressure in the super single tyres. Soil cone resistance was greater in the row after passage of the dual tyres compared with low-pressure super single tyres. There is an advantage in using super single tyres on haulout trucks compared with conventional dual tyres to minimise soil compaction.     

A machine for measuring the suspension characteristics of agricultural tyres

A machine has been developed which is capable of measuring the suspension properties of agricultural tyres under a variety of conditions. The results produced are in agreement with those produced by other workers when these are available, showing clearly that the characteristics of rolling tyres are significantly different from those of stationary tyres. Tyre characteristics are found to have an almost linear relationship with tyre inflation pressure. Various methods of measuring tyre stiffness and tyre damping are used and the results compared.     

Steering forces on undriven, angled wheels

The steering forces at low speed and zero camber angle were measured on undriven, angled wheels using tyres with no tread. The forces were measured in a soil bin using a moist loam soil at different levels of compaction. It was found that the coefficient of side force relative to the wheel was related to slip angle by an exponential relationship. Coefficient of rolling resistance relative to the wheel was a linear function of slip angle in the region zero to 20° but was an irregular function of slip angle at higher angles. The effects of tyre size, load, inflation pressure and soil condition were modelled well using different versions of the tyre mobility number. The most successful version of mobility number was one which incorporated both soil cohesion and internal friction angle. The coefficients of the exponential and linear relationships mentioned above were predicted with varying degrees of success using mobility number.     

Determination of dynamic three-dimensional soil-tyre contact profile

A technique for measuring the dynamic three-dimensional contact profile between a tyre and deformable soil has been developed. The method involves measuring incremental lateral arc lengths of the profile at discrete locations along the contact length and fitting the coefficients of a model of soil deformation at the soil-tyre interface to the experimental data using a nonlinear constrained optimization algorithm (SUMT). Two representations of the measured contact area were compared: (i) the two-dimensional surface which is the union of all points on the original undeformed soil surface which undergo deformation by the tyre; (ii) the final three-dimensional deformed surface. Contact area measurements were made for two different sized tyres at two levels of inflation pressure, dynamic load and slip in two different soil conditions. The contact width, length and area predicted by the technique were compared with corresponding values for static contact between a tyre and a rigid surface.     

The radial damping of agricultural tractor tyres

The damping coefficients of rolling agricultural tractor tyres in the radial (or vertical) direction have been measured. Six different tyres ranging in age from 1 to 16 years have been measured. Factors which most affect the apparent radial damping of the tyre are the inflation pressure, the tyre age, and the surface over which it rolls. The effects of rolling speed, load, torque, amplitude, frequency, ply rating and lug length are also discussed.     

Analysis and prediction of tyre-soil interaction and performance using finite elements

The finite element method [FEM] of analysis previously developed for prediction of rigid wheel-soil interaction is improved and extended to take into account (a) the effect of flexibility of tyre carcass where energy losses now occur in development of mobility, (b) a simpler requirement for specification of boundary condition using input loading, and (c) normal and tangential load stress from the tyre distributed across the tyre-soil interface and varying with slip. The comparisons of analytically computed (predicted) drawbar pull with actual experimentally obtained drawbar pull results for tests in three types of tyres show good correlations. The effect of inflation pressure on development of tyre deformation energy losses can be seen from the analytically computed values.     

Net traction ratio prediction for high-lug agricultural tyre

A study was conducted to determine the accuracy of Wismer-Luth and Brixius equations in predicting net traction ratio of a high-lug agricultural tyre. The tyre was tested on a sandy clay loam soil in an indoor University Putra Malaysia (UPM) tyre traction testing facility. The experiment was conducted by running the tyre in driving mode. A total of 126 test runs were conducted in a combination consisting of three selected inflation pressures (i.e., 166, 193 and 221 kPa) and two wheel numerics (i.e., 19 and 29) representing two extreme types of soil strength under different levels of travel reduction ranging between 0% and 40%. Regression analysis was conducted to determine the prediction equation describing the tyre torque ratio. Marqurdt’s method used by Wismer-Luth for predicting non-linear equation was not found suitable in predicting the torque ratio of the test tyre awing its low coefficient of determination and inadequacy. The logarithmic model was found suitable in torque ration prediction. From analysis of covariance (ANCOVA) the mean effect of travel speed, tyre inflation pressure and wheel numeric on tyre net traction ratio were found to be highly significant, while the interaction of inflation pressure and wheel numeric was not significant. The 193 kPa inflation pressure was found the best, among the three inflation pressures used, in getting higher net traction ratio and higher maximum efficiency. Finally, two models were formulated for tyre net traction ratio; one in terms of wheel numeric and travel speed reduction and the other in terms of mobility number and travel reduction, to describe the tested tyre performance at different soil strengths.     

Estimation of wear life of wheel loader tyre

The purpose of this paper is to analyse the several factors affecting the critical wear life of off-road tyres of wheel loaders, and to estimate the wear life of the tyre. Here, the variation of tread wear depth with service meter hour was measured for two kinds of OR tyre, 37.25-35-30/36PR and 45/65-45-50PR which were used for bucket capacity 7.7 and 9.1–12.0 m³ of wheel loader, respectively. As a result, the critical wear life could be expressed by the initial tread depth, the tyre diameter, the real contact pressure, the roughness of terrain surface, the loading cycle and the amount of slippage. To elongate the wear life, the terrain surface should be controlled to be as smooth as possible and the amount of tyre slippage should be decreased by means of increasing the rear axle load.     

Influence of the axle load, tyre size and configuration on the compaction of a freshly tilled clayey soil

Enhancement of the potential root growth volume is the main objective of farmers when they establish a conventional tillage system. Therefore, the main function of primary tillage is to increase soil’s structural macroporosity. In spite of this, during secondary tillage operations on these freshly tilled soils, the traffic on seedbeds causes significant increases in soil compaction. The aim of this paper was to quantify soil compaction induced by tractor traffic on a recently tilled non consolidated soil, to match ballast and tyre size on the tractors used during secondary tillage. The work was performed in the South of the Rolling Pampa region, Argentina. Secondary tillage traffic was simulated by one pass of a conventional 2WD tractor, using four configurations of bias-ply rear tyres: 18.4×34, 23.1×30, 18.4×38 and 18.4×38 duals, two ballast conditions were used in each configuration. Soil bulk density and cone index in a 0 to 600 mm profile were measured before and after traffic. Topsoil compaction increased as did ground pressure. Subsoil compaction increased as total axle load increased and was independent from ground pressure. At heavy conditions, topsoil levels always showed higher cone index values. From 150 to 450 mm depth, the same tendency was found, but with smaller increases in the cone index parameter, 22 to 48%, averaging 35%. Finally, at the deepest layer considered, 600 mm, differential increases due to the axle load are great enough as to be considered similar to those found in the upper horizon, 36 to 64%, averaging 55%. On the other hand, bulk density tended to be less responsive than cone index to the traffic treatments. Topsoil compaction can be reduced by matching conventional bias-ply tyres with an optimized axle weight.     

Effects of tyre inflation pressure and forward speed on vibration of an unsuspended tractor

Relationships among intensity of vibrations, tractor speed, soil moisture content and tyre inflation pressure are important for the design of tractor suspension systems. This study was designed to evaluate the effect of tyre inflation pressure and forward speed on tractor vibration in the paddy fields of Southern China by using a two-wheel-drive unsuspended tractor with different combinations of forward speed, tyre inflation pressure and soil moisture content. During experiments, the vertical vibration accelerations in front and rear axles and triaxial vibration accelerations of the tractor body were measured using three accelerometers. Fourier analysis was applied to determine root mean square acceleration values in the low frequency range from 0.1 to 10 Hz. The results of the study indicate that tractor vibration is strongly affected by changing forward speed and tyre inflation pressure, and especially by changing forward speed and rear tyre inflation pressure. The research also shows the variation in the pattern of vibration intensity especially at the tractor’s front axle when field soil moisture content is changed.     

Estimation of a three-dimensional tyre footprint using dynamic soil–tyre contact pressures

A method for estimating the three-dimensional (3D) footprint of a 16.9R38 pneumatic tyre was developed. The method was based on measured values of contact pressure at the soil–tyre interface and wheel contact length determined from the contact pressures and the depths and widths of ruts formed in the soil. The 3D footprint was investigated in an area of the field where the pressure sensors of the tyre passed in a soft clay soil. The tyre was instrumented with six miniature pressure sensors, three on the lug face and the remaining three on the under-tread region between two lugs. The instrumented tyre was run at a constant forward speed of 0.27 m/s and 23% slip on a soft soil, 0.48 MPa cone index, 25.6% d.b. moisture content for four wheel load and tyre pressure combination treatments. The 3D footprint assessment derived from soil–tyre interface stress used in this research is a unique methodology, which could precisely relate the trend profile of the 3D footprint to the measured rut depth. The tyre–soil interface contact pressure distributions results showed that as inflation pressure increased the soil strength increased significantly near the centre of the tyre as a compaction increase sensed with the cone penetrometer.