An underbone, or underbone motorcycle, is a small motorcycle built on a frame consisting mostly of one large diameter tubular component. The design is sometimes known as a "step-through" in the West. Although the fuel tank position, the open-frame design which the fuel tank position allows, and the splash guards give the underbone an appearance similar to a scooter, the wheels, engine position, and power transmission are based on the design of conventional motorcycles. Despite this basic difference in design, underbones are sometimes marketed as scooters in the West.
Underbones are popular worldwide, but in East Asian and South East Asian countries in particular they dominate the low cost market segment with their scooter-like ease of use, their appeal to both sexes, and their motorcycle-like dependable handling properties.
The powertrain of an underbone is based on that of a conventional motorcycle. The engine is between the rider's feet and the rear wheel is driven by a regular motorcycle secondary chain drive, Chain enclosure, using sheet-metal covers, is usual.
The fuel tank of an underbone is located below the seat, and it is in this respect only that it differs from a conventional motorcycle, which has its fuel tank between the knees of the rider and a frame member running under the tank from the seat support to the headstock. The underbone arrangement improves ease of mounting and dismounting. Underbones have wheels similar to those of conventional motorcycles.
The technical sophistication of larger motorcycles has been increasingly added to the underbone, with fuel injection systems in the Honda Wave 125i, Yamaha Spark 135iand, since 2007, the Japanese version of the Honda Super Cub. Modern underbones use capacitor discharge ignition for the ignition system, almost all have indicators, and many have electric starters.
Storage on underbones
Most underbone motorcycles sold in Southeast Asia come with a standard steel basket, allowing riders to carry goods. More secure storage capacity is often available with the option of a carrier and a top box. Some top boxes are detachable from the carriers.
Some underbones, including the Honda Wave, Modenas X-cite, and the Yamaha Nouvo, have a lockable storage compartment under the seat. Some have a hook in the area between the riders knees for a shopping bag.
In Pakistan too we should have this type of bike, as new generation is asking for change !All 70 CC bikes look the same (minus the graphics).
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