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The skateboard truck acts as a simple spring. For the first 30 to 40 kg of applied load, there is a linear relationship between the angle of deflection and the applied load. It can be surmised that the relationship follows Hooke�s Law. Force = k x The average user weighs 150 pounds or 68 kg. If this is divided between the two trucks, then the average mass of a user standing on the skateboard is 34 kg per truck. This means that in the majority of cases, the operating range of the truck falls in the first linear region. After 40 kilograms, the relationship becomes less linear. It requires more force to achieve the same deflection of the axle. This is in agreement with a simple mass-spring system. The axle can only deflect up until a maximum point. As it approaches this point, it becomes more difficult to deflect. As the kingpin nut is tightened, it becomes harder to deflect the axle of the truck. For example, when the Grindking bushing is tightened to only three turns, a 70-kg weight will produce an angle of deflection of 21.5 degrees. When it is tightened to eight turns the same 70-kg weight produces a deflection of only 8.8 degrees. This is the difference between a turn of radius 0.58 meters and a turn of radius 1.4 meters. When different bushings are used in the truck, the results vary. The clear bushing, which is the softest, generally gave the most deflection. However, at times it was comparable to the old, worked-in Shorty�s Doh Doh bushing. The Grindking bushing, which is the hardest, generally gave an average deflection when compared to the other bushings. The bushing that gave the least deflection, in most cases, was the new Shorty�s Doh Doh bushing. The difference characteristics of these bushings were noted. At 30 kg and 5 turns, the clear bushing produced a deflection of 14.2 degrees; the old Doh Doh, 12.7 degrees; the Grindking, 12.1 and the new Doh Doh, 9.8 degrees. This is a difference of 4.4 degrees between the bushing with the most deflection and the bushing with the least. During the test it was observed that for large deflections of the axle, there was metal on metal contact between the hanger and the baseplate. This reduced the effectiveness of the bushing. In addition, in some cases, the bushing would come out of the plate that was holding it. Since both of these events would occur during regular use of the skateboard, the results were left the way they were recorded and not adjusted in any way. |