Why do some trucks have a spare set of wheels hanging? Wouldn’t it better to just have all the wheels on the road?

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Why do some trucks have a spare set of wheels hanging? Wouldn’t it better to just have all the wheels on the road?

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Less wear on the tyres and bearings on the raised wheels. They are only needed to bear extra weight so when it is light they raise them for less wear and tear. It might not sound like much but they can do half the distance of the other wheels in some circumstances and if they are driving thousands of kilometres it makes a big difference.

Having the extra set of wheels down adds transmission drag (and thus reduces fuel economy) and also causes more damage to the tyres when turning, so unless you absolutely need them to support the weight of the load, it’s better to have one out of the way.

Those wheels and axles are needed to carry a heavy load. When not carrying a heavy load, they are not needed. If you left them down, those tyres would get extra wear and tear. In some circumstances, it also allows the trailer to be turned around tighter corners.

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