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Soft Tail

The target audience for this suspension design is mostly those who still want the weight benefits of a hard tail, but still want a cushioned ride to reduce vibrations and small bumps in their path. These kinds of frames usually have no moving parts, save for any elastomer or shock HT and possible shock linkages in line with the seat stays. These frames are not designed for rough riding (especially the newer versions, as they won't handle it at all), but more so cross country and sidewalk riding. In the past this type of frame has been hard to develop because of the limitation in materials.

The basic idea is that there are no pivots or moving parts in the chain stay. Point D and the frame component AD are fixed to the main frame. This provides excellent pedaling efficiency because there is no change in the chain stay length (as opposed to the designs on the following pages, on which pedal-jack will be covered), and thus minimal pedaling energy is lost.

How the suspension works is through the flexing of the component AD, and somewhere between points A and B there is a shock absorber. This design was difficult to make due to the necessary flexing of the AB component. Any metal (ferrous or non) would not be elastic enough to be able to bend and return to its original shape, and would become brittle enough to break over time. Engineers then turned towards polymers. Polymers were the best material to be used at this point in time. The material was light, durable and would return to its original shape after being bent.

As progress was made in material development, carbon fiber was introduced to replace the polymer chain stay. This was not only a more durable option, but lighter and more fine-tunable. With careful design to make the chain stay flattened (so they can be bent in the Y direction, but not the Z direction, which is in and out of the page), lateral stiffness is achieved along with a greater flexibility in the Y direction.

The shock can be mounted in line coaxially with the seat stay or with a linkage up near the seat at point B. Having the former, it is possible to adjust the effective spring rate at the axle.

The suspension travel is not significant enough here to account for changes frame geometry, pedal-jack or break-induced suspension lockout. All of the forces in this design are similar to the hard tail frame.

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University of Alaska Fairbanks - PHYS 211X - Fall - Copyright Michael Stanfill 2010©