Search Results

In a series of field experiments we measured the stresses in sand beneath the rubber belt of a prototype belted tractor and beneath single front and dual rear tyres of a radial ply type equipped tractor, using earth stress cells installed beneath the belt or tyres. The stress in the sand increased with increasing axle load for both belt and tyres. The peak vertical stress beneath the belt was about 6 times the average stress calculated as total weight divided by total area of belt. Depending on axle load, the stresses near the soil surface were similar beneath belts and tyres, whereas at 35 to 45 cm depth the stresses beneath tyres exceeded those beneath belts. Stresses beneath individual wheels on the track bogey could be distinguished near the soil surface, but at 35 to 45 cm depth only the average stress could be identified.

The objective of field tests was to analyze and compare the performances of an MFWD wheel tractor and an equal sized rubber track (belted) tractor over a wide range of conditions on Texas soils. When comparing the wheel tractor to the belted tractor across three vehicle traction ratios, two soil types and two soil conditions there was very little difference in fuel efficiency or power delivery efficiency. Both MFWD and belted tractors showed their best performance in the range of 0.4 to 0.5 Vehicle Traction Ratio (VTR). The belted tractor showed its greatest benefit when operated at high VTRs and in soft or loose soil conditions.

Traction performance and fuel efficiency tests were run at the Alberta Farm Machinery Research Centre to compare two different rubber belt tractors with two similar radial tire equipped mechanical front wheel drive tractors. Three different test methods were used in both tilled and untilled clay loam soil. The optimized systems showed only small differences in overall performance and efficiency in good traction conditions and at vehicle traction ratios of 0.4 to 0.5. This was also where both types of vehicle showed their best power delivery performance. Belted tractors showed their greatest benefit when operated at VTRs of 0.6 or higher or in soft or loose soil conditions.

In a series of field experiments we measured the stresses in sand beneath single front and dual rear tyres of a John Deere 8300 tractor, using earth stress cells installed beneath the tyres. The stress in the sand increased both with increasing tyre inflation pressure (constant axle load) and with increasing axle load (constant tyre pressure). Analysis of the experiments using a finite element model showed that the stresses in the top 60 - 70 cm of soil depended mainly on the tyre / soil contact pressure; the influence of the lugs was particularly important. Stresses deeper than that depended mainly on the total load applied to the surface, increasing with increasing axle load. The model was used to simulate compaction in clay soils. Compaction predicted beneath the tyres depended on the strength of the soil, which in turn depends on the moisture content. However, tyre / soil contact pressure and axle load were still important.