Underbones are usually built around a singular tube frame (the "underbone") that supports the whole Most underbones are still using carburetors for the fuel system, with the exception of Honda Wave 125i which uses fuel injection.

While most motorcycles have their fuel tanks positioned at the top front part, the fuel tanks in underbones are located below the seats. All modern underbones use capacitor discharge ignition for the ignition system. Underbones usually carry engines of about 50 cc to 125 cc with the largest displacement being 150 cc for bikes such as the Suzuki Raider 150.