Underbone

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An underbone (弯梁车, literal translation: curve beam car) is a type of motorcycle that uses structural tube framing with an overlay of plastic or non-structural body panels and contrasts with monocoque or unibody designs where pressed steel serves both as the vehicle's structure and bodywork. Outside Asia, the term underbone is commonly misunderstood to refer to any lightweight motorcycle that uses the construction type, known colloquially as step-throughs, mopeds^{[citation needed]} or scooters (see Scooter (motorcycle)).

An underbone motorcycle may share its fuel tank position and tube framing, along with fitted bodywork and splash guards with a scooter while the wheel dimensions, engine layouts, and power transmission are similar with conventional motorcycles.

Unlike conventional motorcycles, underbones are mostly popular in Asia and Greece. In Indonesia, the fourth most populous country in the world, and the largest country in Southeast Asia, almost half the population have a motorcycle, most of which are underbones and scooters. (120 million in 2018, compared to 16 million cars^[1]).