Feb 17 2009
VPP Suspension
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The Virtual Point Pivot system is made up of a double linkage configuration which links together the front and rear triangles of the frame. With virtual pivot designs the two separate linkages, their attachment points and varying lengths can dictate the path taken by the rear triangle when the suspension is active. Because the configuration of the pivot points is almost indefinitely variable, designs and therefore characteristics and rideability of virtual pivot point equipped bikes vary widely. Depending on the aims and wishes of the designer the rear end of the bike can be made to pivot in almost any way.
Due to the constant movement of the two linkages there is no one fixed main pivot point, the pivot point position is constantly changing depending on the actions of the two linkages, in essence a single constant pivot doesn’t exist, which is why this suspension solution is known as ‘virtual pivot.’
One popular implementation of the virtual pivot design is that patented by Santa Cruz ™ and is branded under VPP. The patented configuration of the VPP linkage system creates an rear wheel travel path similar to an elongated S. This path brings with it some minor problems, there is a period where the linkages effectively cancel out each other leading to a very brief lock out of the suspension, however this is at a very precise point in the wheel path.
Each VPP frame is designed to work with sufficient ‘sag’ to provide truly active suspension, this meaning that with the rider on the bike, the suspension has enough positive and negative travel either side of the sag to provide active suspension and to prevent lock out, this allows this type of suspension to deal with some big bumps but also react well to smaller bumps. This will also maximise traction by keeping the rear wheel glued to the terrain!
VPP equipped bikes also pedal well, the system utilises some of the chain pulling force to counteract the natural pedal bob making a smooth ride, however the design occasionally suffers when faced with aggressive climbs and pedalling.
One negative with this type of suspension solution is the weight, as a result of the extra linkages and the strains that are placed upon the small linkages, this can lead to problems in frame durability. As a cure for this fragility the frames are made stiffer leading to a lot more weight needed to support the extra complexity of the frame. Another negative is the ground clearance, having a pivot just behind the cranks reduces the clearance of the rear wheel, which can lead to very tricky riding especially in muddy conditions.
Interested in VPP? Thinking of buying a VPP bike? What do you think of VPP suspension systems?? Why not share your opinions in the forums!
