Our first generation whole sealing box-type mechanical drive variable speed bicycle, easily shift, quickly speed up, going green, fashionable. With the specific three gears, our bicycle can be adapted to any kinds road condition, the cyclist can change the shift during the three gears, the max gear ratio is 3.5-4.88(the circle ratio between the central shaft and the back wheel is 1:3.5-4.88). The whole sealing box-type gear instead of the traditional sprocket wheel, more utility, convenience, sift, the shell of the gear box is high strength aluminum alloy which made by compression molding, the mechanical drive parts is 40 chrome alloy, firm and durable, extend the useful life of the finished bicycle. Gear: Whole sealing box-type with three shifts Frame Material: High Carbon Steel (Q195) Wheel Size: 24"+16" Center Height: 76-88cm Front fork: High Carbon Steel (Q195) Max Speed: 15-20km/h Packing Size: 1130x200x600mm Suitable Crowd: Lady, Elderly (1.2m-1.6m)