In the 1950’s-60’s, production motorcycle of those days (BSA, Norton, Royal Enfield etc.) were basically styled in the same traditional manner.
British motorcycle enthusiasts back then modified those stock motorcycles to replicate the road racing motorcycles of those days. And thus the Café Racer was born.
The stock tank was replaced with customized tanks with knee recess so that the rider could grip the tank with his knees while riding.
The front foot pegs were replaced with rear set foot pegs and accordingly the normal handle bars were replaced with clip on handle bars. Another signature modification on the Café Racer is a humped rear seat to mimic the road racing motorcycles of those days.