Scooter Performance Racing Gear Set For GY6 50cc 80cc 100cc (17T/49T) 139QMB 1P39QMB 4T Performance transmission gear set designed for 139QMB 4-stroke 50cc and ATVs with standard or big bore engines.This gear set features a 49/17T ratio, providing a balance between acceleration and speed.Upgrading to this gear ratio can result in an increased speed of up to 10mph.The kit uses a simple press-fit installation method and can be installed with basic tools and mechanical knowledge.Suitable for GY6 platform engines including 50cc, 80cc, and 100cc variants.Confirm compatibility with your engine model before installation.