Tension Link suspension bicycle

This is an open source suspension bike design- it is a non patentable design and it is free for anyone to use in any manner they wish as long as they credit the source of the design. I fully encourage people to modify it and improve upon it. My reason for creating this design was to build a suspension bike with good performance that features simple/low cost construction, has minimal maintenance and can be easily customized in terms of sizing and geometry. There are several reasons for open sourcing the design but the main reason was to be able to make it available free of charge to all the small custom builders out there- the design is really well suited to the needs of the small custom builder that wants to offer a suspension bike but maybe has been put off by the expense and complexity of previous designs.

So why did I choose a URT (unified rear triangle) design? Isn't a URT an inherently inferior design? Well, yes and no -depending on your point of view. A URT would be a poor choice for a pure downhill race bike- it simply has too much unsprung weight due to the weight of the drivetrain and the long travel necessary for a downhill bike would cause the BB to move too much. The axle path is great but I feel there would be too many compromises that would lower the overall performance to an unacceptable level.

An all-mountain or XC bike is a different beast and for this application a properly designed URT can be very competitive. I wanted a three to six inch travel design that has an up/rearward axle path with minimal chain growth. There are several ways to achieve this- a gearbox design or a roller placed near a high pivot would work but I felt those designs were best suited toward downhill bikes. In the end I came up with a design that has similar kinematics to a floating BB design with the simplicity of a URT. With this design the main pivot sits directly over the BB and is close to the rider's center of mass so the suspension is always working, even when you stand so the suspension is very active like a floating BB bike -unlike the old URT designs which were not active at all. With a URT there is also zero chain growth, so a belt drive system could be used as could an internally geared hub or even a single speed system -without the need for any kind of tensioner.

This design has a large torsion tube for the front end and a simple triangulated rear end. This allows for a very efficient structure in terms of torsional stiffness and it is very simple to construct. All loads are fed into the ends of structural members so the design can be very light weight and unlike many designs, this bike can be built with very short chainstays- the "proof of concept" prototype has 15.75" chainstays and still has decent tire clearance. Altering the frame size does not significantly alter the position of the suspension system components, hence it does not need to be completely redesigned for every frame size. It also has a very low stand over height.

How the suspension works: as the rear wheel hits a bump it moves upward and backward and the BB moves with it, causing the pull rod/radius arm (tension link) to actuate the rocker arm that compresses the shock. It's a very simple and effective system that pedals very well and is still very good at soaking up large square edged bumps. Everyone that has ridden it has been amazed by how nice the bike rides (even with ancient suspension components) and everyone has expressed a great deal of surprise in regard to its excellent torsional stiffness.