He makes heavy investments in the rubber tire business. Studdable tires are manufactured with molded holes on the rubber tire tread. The aircraft also left rubber tire debris. It also pioneered some synthetic rubber products, including developing the first synthetic rubber tire. Woojin Industrial System Company Limited, supplied urban rubber tire trains for Line 4. The rubber tire engages a center rail that begins halfway through the first spiral. A hard rubber tire on a bicycle is just as rideable but is bone jarring.