In 2003 Specialized introduced the Brain, an external inertia valve designed to effectively eliminate pedal bob. The system utilizes a brass weight inside a cylinder situated atop the non-drive-side chainstay, near the rear dropout, and connected to the shock directly or through a hose. The weight closes the shock valving and deactivates the rear shock at rest. Upward force from rough terrain displaces the weight, opening the valve and engaging the suspension. In the original Brain mechanism, when the terrain evens out, the weight returns to its original position through a return spring, and deactivates the shock again. The position of the weight near the rear axle is designed to prevent downward pedaling force from affecting the mechanism while optimizing response from terrain. A newer version of the Brain was developed that utilizes the rebound hydraulic fluid flow to return the weight to its rest position instead of relying on a return spring. This was developed to address a noticeable delay in the shock activation/deactivation.
The VPP (or Virtual Pivot Point) is a linkage designed bike that is built to activate the suspension differently depending on what inputs the suspension has received. When most people think "Virtual Pivot", they think of the VPP™ bikes by Santa Cruz™ and Intense™. These bikes use a specific type of Virtual Pivot design that was originally developed and patented by Outland Bicycles™ about 10 years ago. The patents cover a specific linkage configuration and rear wheel travel path that is designed to aid the pedaling performance of a rear suspension bike without negatively affecting the overall bump absorption capabilities of the suspension. Yeti Cycles has created a unique rail system to eliminate pedal jacking. The DW-Link is another design licensed to Iron Horse and Independent Fabrications. Giant's Maestro is yet another design that works very well. The Maestro and DW-Link suspension designs are just as efficient as the FSR system and the VPP. They also have the benefit of having a progressive spring rate. Patents have drawn definite lines among the manufacturers.
To define a VPP/DW-link/Maestro suspension design, imagine a line that follows the path the rear axle takes as it moves through its travel. Continue it into a complete circle. The center of the circle will be the pivot point. It will be a virtual point in space and not an actual pivot on the bicycle. It can either be a fix point or one that moves around as the suspension compresses (floating), depending on the design.
The VPP family of suspension systems are in fact four bar designs. They have short links instead of the longer links on a conventional four bar (chainstay and rocker).
The VPP (Virtual Pivot Point) system used by Santa Cruz and Intense, also claims to have reduced the problem of pedal bob. Soon after the VPP was introduced, the creation of the Progressive Suspension 5th Element rear shock (based on Currnut's platform damper) near the beginning of the Millennium allowed riders to adjust almost any frame, regardless of design, to be pedalled without the pedal bob that plagued earlier designs. Other companies have followed Progressive's lead (mainly Manitou with its SPV system based on the 5th Element and Fox's ProPedal which uses a shim stack rather than an air pressurized valve) and a revolution in suspension design is under way. However, these 'intelligent' shocks always have to compromise between their resistance to bob and performance with small bumps. VPP designs help reduce pedal bob by virtue of their design and thus can use a rear shock with little or no platform damping. This allows the suspension to be "fully active" and provides great small bump performance while also remaining plush on high speed descents.
Many think the tried and trusted technology of the four bar linkage with a comparatively simple shock still offers the best performance. However, the four bar linkage causes pedal bobbing, lockout, and brake jack. With the rise of more complicated shocks and a larger market share of full suspension bikes mountain bike suspension tuners have now arrived. It is now possible to have shocks tuned to individual rider's desires.
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