ROADSTER-BICYLE 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).
The handle design 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 heavywieght 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 lighweight 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.