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Old Apr 23rd 2017, 09:55 PM   #1
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Race Car vs. Truck Tire Wheels Rot. Dynamics

Using your knowledge of rotational dynamics and material properties,
explain why large, thick tires are used more often on heavy-load-bearing trucks (or mountain bikes)
whereas smaller wheel and thinner tires are better for sports cars (or road bikes). For concreteness,
you might compare a wheel with an 30 cm Al rim and 10 cm rubber tire to a wheel with 25 cm
Al rim and 4 cm tire. As an estimate, that you may improve upon with your own research, you
may use that the density of aluminum (a common choice for wheel rim) is ρAl ≃ 2.7 g/cm3 and
its Young’s modulus is YAl ≃ 70 GPa, whereas for generic rubber the density is ρ <∼ 1 g/cm3 and
Y <∼ 0.1 GPa. (For very large construction vehicles, the rubber is considerably reinforced, but this
does not change the reasoning.)
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Old Apr 27th 2017, 01:35 PM   #2
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It should be fairly evident why wide tires are better for heavy trucks on the basis of pressure upon the road.
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Old Apr 27th 2017, 02:06 PM   #3
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The question is very poorly worded, but I believe its not about the width of the tire profile but rather about the height of the tire profile and/or the thickness of the rubber that makes up the tire. Obviously the thicker the rubber the greater the mass of the tire and hence the greater its moment of inertia. And same applies to wheels and tires that have larger diameters. So by this reasoning the smaller the diameter of the tire and the lighter the rubber the less torque is needed to get it to rotate faster, which is good for sports cars and lightweight bikes. But where heavy loads are concerned and you are less interested in acceleration the thicker rubber material helps reduce stresses in the tire and extends its useful life.
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