Many cyclists prefer to ride at night, however, conventional safety warning devices at the front and back are not obvious enough, resulting in frequent accidents. When cycling in the city, attach the Racing Wheel to a bicycle wheel and it will begin to charge after it’s switched on. If the device is connected to a mobile application, symbols and words can be displayed on the wheels of the bike and the warning light can be controlled via the application to ensure the safety of the cyclist. Furthermore, the cyclist can use the device as a speed recognition device during a bicycle race and the speed information will be displayed on the application. To use Racing Wheel, place it between the chain and the back bicycle wheel. Switch on the mobile application and charging device, connect the two and the device will start to charge when the wheels rotate. One can also detach the device and use it as a ‘power bank’ after riding.