What are the telltale signs that a bike is not designed to handle a heavier rider, considering factors such as material composition, frame geometry, and component durability? For instance, are there specific weight limits or rider height restrictions that manufacturers adhere to when designing bikes, and if so, how can a prospective buyer determine whether a particular model is suitable for their weight class? Furthermore, are there any red flags that a heavier rider should look out for when test-riding a bike, such as unusual creaking noises, flexing of the frame, or excessive wear on the wheels and other components? Additionally, how do factors such as riding style, terrain, and intended use affect the suitability of a bike for a heavier rider, and are there any modifications or upgrades that can be made to a bike to make it more suitable for a heavier rider?