The engineering principle of KOO is counterintuitive. As the world's first hollow dual-wheel, Jose Vinaroz made a bold decision in 2007 to remove the traditional central axle. The absolute blank space at the center of the wheel requires us to establish a new mechanical distribution between the heavy zinc alloy frame and the PA wheel core. To support a maximum load of up to 130 kilograms for the KOO model, workshop technicians repeatedly overturned and reconstructed the stress logic of the castings. This restrained design of directly hollowing out the mechanical skeleton ultimately found solid physical support in the rigorous tests of EN12528 and BIFMAX5.1. It was proved that removing the central axle did not weaken the chassis; instead, it made the flowing spatial order more pure.