Ridley Astr RSvsKanzo Fast

The Ridley Kanzo Fast, launched in 2021, stormed onto the scene proclaiming itself the world's fastest gravel bike. It essentially adapted the aerodynamic prowess of Ridley's Noah Fast road bike to gravel, with truncated tube shapes and integrated components designed to cut through the wind. Its market position has been as a purebred gravel racer, leaning heavily into speed on hardpack and tarmac-like gravel roads. Now, for 2025, Ridley introduces the Astr RS, framed as the "gravel racer of the future." This bike evolves the Kanzo Fast's race DNA but also incorporates the impressive off-road capabilities of Ridley's adventure-oriented Kanzo Adventure. The Astr RS addresses modern gravel racing's demands for even wider tire clearance, pushing the envelope to 52mm for a 1x setup and a still-generous 47mm with a 2x drivetrain. This marks a significant departure from the Kanzo Fast's more limited 42mm maximum clearance. While both bikes are unequivocally built for speed, the Astr RS represents a more comprehensive approach to contemporary gravel racing. It aims for a lower system weight (the Astr RS test bike came in at 7.82 kg, nearly a kilogram lighter than a comparable Kanzo Fast at 8.76 kg for size M) and a greater degree of adaptability to increasingly varied and rough race courses, making it a more versatile race weapon for the modern gravel circuit.

The Kanzo Fast is a stiff, responsive machine that rewards aggression. Reviewers consistently note its ability to pull away quickly and hold speed with minimal effort on compact surfaces. It's an intuitive bike that encourages pushing hard, feeling remarkably fast on gravel highways and even tarmac. However, this stiffness comes with a trade-off: while its lowered seat stays and D-shaped seatpost offer some comfort on smaller bumps and high-frequency vibrations, the ride quickly becomes uncomfortable on rooted trails or when encountering larger hits. Its handling, described as stable and predictable at speed, can feel cumbersome and demand a firm hand on technical singletrack, struggling with tight corners. Stepping up, the Astr RS takes the Kanzo Fast's race DNA and refines it for a broader range of gravel conditions. It delivers excellent power transfer and nimble acceleration, partly due to its lighter system weight. Reviewers found it effortlessly accelerates on flats and steep climbs and holds speed with impressive efficiency. The Astr RS largely relies on its voluminous tires for comfort; the 47mm Vittoria Terreno Dry tires, for example, do most of the work absorbing impacts. The frame itself remains stiff, crucial for power transfer, but its design accommodates greater compliance through wider tire options. Handling-wise, the Astr RS aims for precise, direct control. It retains the Kanzo Fast's agile chainstays (425mm) while increasing the top tube and wheelbase slightly for enhanced stability at higher speeds. This combination, along with the option for wider tires, means it can carry speed through loose gravel corners with greater composure. The cockpit choice, a narrow 36cm at the hoods for aero efficiency, requires riders to move their hands to the wider drops for optimal control on technical descents. While the Kanzo Fast excels on smooth, fast routes, the Astr RS offers more reserves for rougher terrain, making it a more capable and versatile racer on demanding gravel courses.