Masters Theses

Date of Award

8-1996

Degree Type

Thesis

Degree Name

Master of Science

Major

Biosystems Engineering Technology

Major Professor

John Wilkerson

Committee Members

Luther Wilhelm, Thomas Samples

Abstract

A tire's main function is to provide traction for the vehicle to which it is attached. A turf tire must be able to provide the necessary traction without causing excessive turf damage. Therefore, it is extremely important to evaluate turf tire design components, such as sipes, not only for traction considerations but for turf damage as well.

A Ford lawn and garden tractor was operated on a tall fescue, Festuca arundinacea Schreb, turf surface while towing a constant drawbar load. During a test, the tractor was operated in second gear and the engine speed was maintained at 3000 RPM (approximately 3 mph). A complete test run consisted of a pass down and back through a 200 ft course. Data was collected in both directions through the course and averaged to reduce the effect of slope. Turf samples were taken at the end of each test run. Six blades were removed and photographed using a camera, a specially designed camera stand, and a photo gray background. The turf pictures were then analyzed at a later date for fresh tearing and bruising. Damage was recorded as a percent of total blade area.

Included in each test were five variables: day, surface moisture, axle load, draft load, and tire sipe design. Day was defined simply as the day the test was run. The free-surface moisture level was described as either true or false, meaning that either the turf surface had moisture on it (true) or the turf surface was dry (false). The axle load was defined as the weight of the tractor, the operator and additional ballasting. The draft load, placed on the tractor by the dynamometer, had values of 0, 150, 300, and 375 lbs. Four sets of tires, each of the same general construction, were used for these tests. It was believed the only difference between the sets of tires was sipe density. The sipe density had values of 0, 50, 100, and 200 percent. During data analysis it was discovered that for tire sets B and D the left side tire was larger than the right. This proved an interesting problem.

Analysis proved that as the draft load increased the percent slip also increased. Also proven was the fact that as the axle load increased the percent shp decreased. These conclusions were as expected. An increase in sipe density appeared to decrease the amount of drive wheel slip. It was also shown, when given two drive tires under the same load and drive conditions, the small tire will have a greater amount of slip than the larger. Thus, a higher percentage of the draft load is transferred to the smaller tire. Turf damage assessment for these tests proved inconclusive. This was caused by the fact that the sample size was too small. However, it was observed that turf damage tended to occur in areas that were already stressed. Turf damage was also observed to increase in severity as the number of passes over an area increased.

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