|MadSci Network: Engineering|
Short answer: Because a tire can only carry so much weight on it, and by using more tires, the load is distributed. Long answer: Trucks and buses have most of their weight towards the rear (in buses, most of the weight is because of the engine.) Keep in mind that those vehicles are designed to have their weight biased towards the rear axle (or axles). This is done for many reasons, particularly because the rear axles have the driving tires, and those tires need a good amount of weight above them so that they don't just spin. Another reason for the rear weight bias is that steering becomes lighter, and the amount of power steering required is reduced. The weight of a bus or a truck is so much that more than two axles are needed, regardless of what tire configuration is used, and it would not be practical to put two front axles (because of steering). So rear placement is preferred. I hope that answers your question, Your mad scientist, Aurelio R. Ramos
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