Zenith Motorcycles was a British motorcycle and automobile manufacturer established in Finsbury Park, London in 1903,[1] by W.G. Bowers.Automobile manufacture only lasted from 1905–1906.
source/image(PrtSc): classic-motorcycle.com
Fred W. Barnes was hired as chief engineer in 1905, and patented the “Gradua” variable-ratio belt drive transmission that year. The Gradua system simultaneously changed the diameter of the crankshaft belt-drive pulley to alter the drive ratio, while moving the rear wheel forward or back to maintain belt tension.
The mechanics of the Gradua gear were a variable engine pulley worked by a handle, with simultaneous correction of the belt length made by sliding the rear wheel backwards or forwards in the fork slots. Its advantage showed itself most effectively in speed hill climbs.
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This Zenith is equipped with a sturdy and reliable 6 HP ( 770 cc) JAP engine with bore and stroke of 76×85 mm and is in concourse condition. Variable drive ratios proved a significant advantage in competition, leading riders of other marques to complain the Gradua gave an unfair advantage./wikipedia
