Underbone Motorcycle Design

There are many kinds of small motorcycles on the road. For example, there are mopeds which are actually a cross between motorcycles and bicycles. There are also scooters.

Another category of small motorcycles look like a cross between full size motorcycles and scooters. These are underbone motorcycles.

Underbone motorcycles are very popular in East and Southeast Asian countries. That's because are cheap, reliable and fuel efficient.

These motorcycles are built around a single tube frame, which is called the underbone. This underbone supports the whole vehicle and runs low all across the length of the motorcycle. This arrangement makes it possible to provide a step that is similar to a scooter's floorboard.

The engine of an underbone motorcycle is usually located under the frame, laid flat on its side. The design also shares the same manual transmission found in full sized motorcycles but with an automatic centrifugal clutch. Some underbone motorcycles have manual clutches.

An underbone motorcycle still utilizes a chain drive to turn the rear wheel around. They are ridden like regular motorcycles. The engine usually ranges from 50 cc to 125 cc which is much less powerful than normal motorcycles. Most underbones use a carburetor for the fuel system although the Honda Wave 125i uses a fuel injection system. The carburetor is usually located on the top front part of the engine while the fuel tank is placed below the seats. For the ignition, an underbone motorcycle uses a capacitor discharge ignition system.

While the engine displacement is small, an underbone can reach highway speeds up to 110 to 120 kilometers an hour. In many Asian countries, people are allowed to ride underbones on expressways.

In Southeast Asia, a newly purchased underbone motorcycle has a steel basket to allow the rider to put goods in it. Optional removable storage compartments can also be installed through a bracket. The Honda Wave and Modenas X-cite come with an additional storage compartment under the seat.

Many riders modify their underbone motorcycles. Some of the modifications are done for aesthetic beauty. This includes custom painting the motorcycle or installation of neon lights or small sound systems. Some are fine tuned for racing such as increasing the engine power or tuning the suspension system.

But the popularity of underbones in Southeast Asia has produced a darker problem. Illegal underbone drag racing has become rampant in the streets. This poses a problem because underbones do not have enough protection in event of a crash. Police forces have frequently launched operations to lessen illegal underbone drag races.