The first successful sprung safety bicycle was the 1886 Starley & Sutton Rover. The idea was resurrected in the late 1890s and early 1900s to try out suspension parts that manufacturers thought might be useful on the new ‘motor bicycles’.
While American bicycles offered sprung front and rear forks by way of suspension, British firms experimented with springing built into the frames. The well-known cross frame design was also initially introduced as a form of suspension. The most successful integral spring frame design was made by BSA in 1900.
The Simplex Zweeffiets is an interesting concept. Simplex seems to have started making cross-frame bicycles using the Centaur design the same year that the Centaur Cycle Co went out of business (1909). The Zweeffiets incorporates the central cross tube to the rear axle but the top tube is replaced with a leaf spring and the seat tube also has a spring. The steering head is reinforced.
Up until trying this example my experience has been limited to early 1900s BSA spring frames, which I find a bit unnerving simply because I’m not used to a bicycle that bounces unexpectedly. Whereas the BSA has springs built in to its top tube, the Zweeffiets is a more practical design, its leafspring providing only a minimal level of suspension while riding so that it doesn’t flex unnecessarily.
1953 Simplex Zweeffiets Spring frame