Zenith Gradua

Zenith Motorcycles was a British motorcycle manufacturer established in Finsbury Park, London in 1904. Zenith motorcycles used engines from various suppliers, including Precision, Villiers and JAP. Under chief engineer Frederic "Freddy" Barnes, Zenith developed the "Gradua" gear, a variable pulley which adjusted the length of the drive belt by sliding the rear wheel backwards or forwards in the slots. This gave Zenith a great advantage which competitors claimed was unfair and many clubs banned the Gradua Zeniths, who simply included the word "Barred" in their badge. In the 1930s Zenith hit hard times and closed down production. Read more on Wikpedia

Lowry refers to the motorcycle in his short story 'Enter One In Sumptuous Armour'; "Fine motorcycles whizzed by or splashed past us: a Zenith Gradua...." (Pg. 233)