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3. Results and Discussion Product 1:MTD Yard Tractor After each of the six vibration tests, the level of tire damage was measured by depth and width of the tire cuts. The results from the front tire and also from the back tires for each test were averaged for ease of comparing total tire damage, Table 3.1. The measurements denoted by 0 mm indicate damage that was immeasurable. It is important to note that there were not three points of measurable data on each tire for every test, as there was not visible damage in every case. Therefore, it is important to use not only the data collected but also the images of the damage when evaluating the six vibration test. Analysis of the depth data collected for the evaluation of the current versus the proposed method indicated that the current ASTM D4169 produced the highest levels of damage with an average of 3.0 mm. The front of the yard tractor was the heavier end and so the damage tended to be worse on the front tires than the rear tires. Very little damage occurred on the rear tires. According to the product manufacturer, the damage observed in this vibration test far exceeded typical field damage levels. The damage produced during the proposed ASTM D4169 profile produced lower levels of damage than the current profile, 1.7 mm. A visual inspection of the tire damage, Figure 3.1, confirms that the damage was indeed much more severe for the current profile. Between the two modified tests, the Modified 1 vibration test produced the highest damage, Figure 3.3, at 3.8mm on the front tires and 1.8mm on the rear. Modified 2 produced 1 mm of damage on the front tires, Figure 3.4, and only produced minor scuffmarks on the rear tires, 0.5 mm in depth. The last two vibration test run were the ISTA Steel spring vibration, 0.54 Grms, for a time of 60 minutes and 180 minutes. These tests produced similar damage in both depth and width. Table 3.1: Vibration Test Depth Results For MTD Yard Tractor. Front Average 3.0 1.7 3.8 1.0 1.3 1.2 Current ASTM D4168 Proposed ASTM D4169 Modified 1 Modified 2 ISTA Steel Spring 180 ISTA Steel Spring 60 Rear Average 0.0 0.0 1.8 0.5 0.7 1.5 Depth of Tire Damage 22 ista views • December 2015 • www.ista.org Laboratory Evaluation of ASTM D4169 (Current and Proposed) Vibration Profiles > CONTINUED FROM PAGE 21

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