Bicycle with rhombus-like gear with circularly curved apexes

A bicycle comprising

• a frame, a seat, and handlebars,
• a rear wheel supported on said frame,
• a front wheel supported on said frame and controlled by said handlebars,
• a driven gear with gear teeth supported on said frame for rotation with and driving said rear wheel,
• a sprocket gear with gear teeth supported for rotation on said frame,
• crank arms and pedals supported thereby, supported on said frame for rotary motion and secured to said sprocket gear for rotating it by pedal operated motion,
• a drive chain surrounding said sprocket gear and said driven gear and interconnecting said sprocket gear teeth and said driven gear teeth for transferring motion and force therebetween,
• wherein
• said sprocket gear is constructed of rigid sheet material, is a rhombus shape having flat sides, with a major and minor axis, and four regions of circular curvature spaced 90.degree. apart at the major and minor axes connecting said flat sides,
• said pedals being secured on said sprocket gear at an acute angle to and forward of said major axis relative to said bicycle frame, to provide a constant low gear ratio when the cyclist's legs are moving the pedals backward and forward, and a constant high gear ratio when the cyclist's legs are moving the pedals up and down, and
• the gear ratio changes abruptly from said constant low gear ratio to said constant high gear ratio and from said constant high gear ratio to said constant low gear ratio only at regions spaced apart 90.degree. in the rotation of the sprocket gear.