How did multiple-speed gears improve bicycles after 1900?

After 1900, the introduction of multiple-speed gearing represented the most significant technical advancement in bicycle design. These systems, which include derailleur gears and internal hub gears, fundamentally improved the cycling experience by allowing riders to match their pedaling speed, or cadence, to varying terrain.12

By enabling the rider to adjust the gear ratio—varying the size of the sprockets and chainwheels—the rear wheel can be made to turn faster or slower relative to the crank. This mechanical flexibility makes it easier to maintain efficient pedaling across different inclines and conditions. While early developments included two-speed internal hubs and later three-speed versions, the evolution of derailleurs eventually allowed for a much wider range of ratios. By the 1970s, the popularity of "10-speeds" demonstrated the consumer demand for these versatile machines, which eventually paved the way for modern systems offering up to 30 different gear ratios.21