Bicycle suspension redesign

We redesigned the seating and suspension system of a common roadster bicycle, and also added a small carrier for groceries.

The origional design

A stock roadster bike in India looks like the preceding picture. Several manufacturers produce this design with very minor variations.

The design features:

  • A metal-tube frame connected via custom-made lugs.
  • 28" wheels.
  • A jointed metal-tube based braking system (as opposed to a brake-wire based system).
  • A handle design that is associated with the braking system. The handles are aligned longitudinally with the bicycle -- i.e. perpendicular to the handlebar.
    • This creates a constraint for the rider -- the have to keep their knees on the insides of the handles.
  • There is no suspension except for heavyweight tires -- typically 1.5" wide.
  • The seat has dual heavyweight coil-springs to absorb bumps at the sitting location.

Our modifications

We created a carrier design below the top-tube, by creating a triangular frame extending from the down-tube to the head-tube. The frame was wide at the front handlebar area (30cm) and narrow just below the seat (10cm). It was useful for groceries.

We removed the seat tube and attached 3 staggered iron strips above the top-tube in a leafspring like formation, to be somewhat flexible at the back. We added dual lightweight coil-spring containing cylinders (in a piston-like structure) to both sides of the rear-wheel-spindle. We attached the top of these 2 springy cyclinders to the back of the leaf-spring system and added a seat on top.
This design moved the riding position slightly backward, creating a small forward angle in the vertical pedalling thrust. But it gave good shock-absorption on very bumpy roads and increased riding speed substantially. Also, with the seat having been moved back, the rider contsraint associated with the handle-design was removed.