What is the Shimano hierarchy for road bike components?

The Shimano hierarchy for road bike components consists of four main groups: Dura-Ace, Ultegra, 105, and Tiagra. Dura-Ace is the top-tier group, followed by Ultegra, 105, and Tiagra in descending order of performance and price. Each group offers a range of components such as shifters, derailleurs, brakes, and cranksets designed for different levels of performance and budgets.