Single-speed Chain Tensioner / Sprocket Guide for Folding Bikes (fits 11T or 13T rear derailleurs) What it does Converts multi-speed folding bikes to a reliable single-speed setup by maintaining consistent chain tension. Prevents the chain from slipping off the crank using a spring-driven guide that adapts to different gear sizes. Key benefits Less effort while pedaling: provides steady, optimal tension so you expend less force and enjoy smoother pedaling. Improved drivetrain reliability: reduces chain drops and noise by keeping the chain aligned and tensioned. Simple, compact solution: lightweight and small design minimizes added bulk and preserves folding-bike portability. Compatibility and function Designed specifically for folding bikes using an 11T or 13T rear derailleur. Works as a sprocket guide and chain tensioner; the spring mechanism accommodates small variations in gear size while holding the chain in place. Performance and attributes Spring design adapts to different gear sizes to prevent slippage and maintain steady chain tension. Small, lightweight construction for minimal impact on bike weight and folding function. Easy to install and use—suitable as an upgrade, replacement, or accessory for everyday riders. Practical use scenarios Commuting: Convert a multi-speed folder to a single-speed for a simpler, lower-maintenance setup on short urban rides. Travel and storage: Use on folding bikes taken on trains or stored in tight spaces where a compact, reliable drivetrain is preferred. Maintenance and repair: Replace or add a sprocket guide to stop intermittent chain drops and restore consistent chain tension after drivetrain changes. What you get A compact, spring-loaded chain tensioner/sprocket guide designed to fit folding bikes with 11T or 13T rear derailleurs. Easy to fit and ready to use.