This particular idea was pioneered by GT as a basis for their I-Drive suspension system.  This system places the bottom bracket along with the crank assembly component on a pivot point that is separate from both the front and rear triangle of the bike resulting in the bottom bracket and crank assembly effectively floating.  This is the unique feature that distinguishes the floating pivot design from other active full suspension systems which have the bottom bracket mounted on either the front or rear triangle of the bike.

The floating bottom bracket design maintains most of the quality characteristics associated with VPP and horst link/four bar suspension systems.  The floating bottom bracket design has the technology within the design to minimise pedal bob (if correctly calibrated) and also remains resistant to braking compression.  This means that even under braking the suspension remains active making for a smoother riding experience for the user and improves the traction of the bike by keeping the back wheel in contact with the ground for longer.

It is general opinion that the floating bottom bracket design has potential to be a brilliant all round solution, however although models have improved, there is still a lot of improvement to be done.  One problem with this type of suspension is the added weight which comes purely due to the complexity of the design, although the current I-Drive is now much lighter than the original, it is still a little on the heavy side, making climbs tricky.

 It is not just the I-drive that utilise this floating bottom bracket design, there are a couple of other manufacturers that make use of the idea, however they each have their draw backs.  One flaw comes from having the crank assembly mounted on a floating pivot, because of this a special front derailleur has to be fitted to counteract the motion created at the pivot point, despite this there are instances and cases of shifting trouble on the front gears.  It is also noted that this type of suspension causes the seat post to be at a slightly unfavourable angle with some riders making a correct pedalling position difficult to achieve. 

All in all, this system has some good points, eliminating pedal bob and compression under braking, however it still lacks some of the simplistic refinement found in other suspension solutions.

Don’t agree? Have your say in the Forums!

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No matter what characteristics an object has, as long as it is on this big rock we call earth, it will be governed by basic physical laws.  These laws of physics therefore impact upon any object, movement involving these objects is also regulated by constant variables included within these rules, and so the way the object reacts to these rules can be anticipated. This is the concept that the DW Link suspension system relies upon to work.  The DW link system balances out the forces created from the bikes movement resulting in arguably the best suspension system to date.

The rules that the DW Link is based upon are made up of simple physics:

1.      Every rider has the same ‘centre of mass’ therefore weight distribution is constant

2.      Laws of physics dictate that every action has an equal reaction.  Therefore if a bicycle accelerates forward, the rider’s total mass is transferred backwards and so the ‘centre of mass’ shifts backwards.  This is the main reason for suspension becoming locked out during braking and acceleration, the weight shift causes compression of the rear suspension and causes a bobbing motion.  This causes ‘bob’

3.     Pedalling causes forces on the drive chain which results in fluctuations of the chainstay lengths, these fluctuations are reflected by the amount of pedal feedback through the suspension, the less change in the chainstay length during pedalling, the less pedal bob.

4.     Pedal bob is usually counteracted by extra dampening in suspension systems, this detracts from the efficiency and is usually only necessary for less sophisticated suspension, DW link suspension minimises the amount of dampening used and so the suspension is more reactive to minor deviations on the trail.  This gives better traction on the terrain aiding in changing of direction and changing in speed.

For more information on DW link visit www.dw-link.com , do you own a DW link equipped bike, does this suspension system work, have any questions?  Why not visit the Forums

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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!

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The 4 bar design consists of 3 pivots, one behind the bottom bracket, one at the top of the seat stay and the horst link pivot just in front (and below) the rear wheel drop out.

The patent that Specialized bought and subsequently licensed out concerns the position of the pivot below and in front of the rear drop out which is known as the horst link.  The horst link design allows the rear axel to move through a more complex arc than that associated with a single pivot design, this allows more vertical travel for the rear wheel, allowing it to cope better with bumpy terrain and maximising the time it spends in contact with the ground, granting better traction.

An advantage of the horst link design is that as the pivot is located in front and below the rear drop out the suspension forces and the drive train forces are separated and therefore can work independently.   This means that despite a change in speed, either accelerating or decelerating the suspension remains fully functional, this essentially eliminates the brake jack syndrome that plagues other types of suspension solution.

In regards pedal bob, reviews are quite varied, so much so that Specialized have designed a specific component to collaborate with their FSR suspension to minimise pedal bob, this is known as the ‘brain’ which I will discuss in future articles.  It seems that depending on the overall design pedal bob feedback can be varied, however in theory as the drive train and the suspension are separated the chains leverage effect over the suspension is reduced and therefore so should pedal bob.

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The single pivot rear suspension system is the simplest rear suspension design available.  Simply put the design involves the rear axle being connected via a swingarm to a shock unit (usually a coil and oil or air shock) via leverage on a single pivot point, hence the name single pivot suspension system.  This suspension type was the most common during the rise of mountain bike suspension and as a result has been around for a while, the system itself was derived directly from the type of system used on motorcycles.

The single pivot point position influences the entire movement of the rear swingarm as a result the location of the shock and leverage point can affect the way the bike as a whole performs.  Depending on where the pivot point is positioned can dictate how efficient the bike is and also how well the suspension itself performs.

There are a few negative points from this type of suspension design that you may expect from technology that is getting a little dated, as a result of the swing arm being mounted on a single pivot bikes with this type of set up tend to suffer from compressive brake jack.  This is a term given to when the shock compresses under braking, the effectively reduces the functionality of the suspension when decelerating.  This can lead to a bumpy ride at low speeds. 

Pedal bob is also a problem that plagues this type of suspension mechanism, in low gears, the cranks and cassette pull together, which pivots the swing arm causing the shock to compress, this again leads to a bumpy ride and pedal bob reducing the efficiency of the bike as a whole.

Wear and tear is something that single pivot suspension suffers from more so than other suspension solutions, the reason being that all the movement, both horizontal and lateral from the swing arm goes through the same single pivot point, this movement through the pivot in all directions can lead to more wear and tear on the bearings and bushes due to excessive loads being transferred through the pivot.

On the upside the single pivot design is very simple and doesn’t involve many moving parts at all.  As there is not a lot of moving parts, the scope for variation is quite limited, even manufacture to manufacture the single pivot systems are fairly similar, because of this, although wear and tear may be an issue, repairing it isn’t.  The bearings and bushes used in the single pivot system are generally of standard sizes and as a result are readily available and affordable.

In conclusion, single pivots are certainly not perfect and are flawed in the ways highlighted above, however as a cheap, easily maintainable solution to rear suspension it can be argued that if you can overlook the detrimental effect on the pedal efficiency and the bumpy ride at low speeds, the single pivot solution is definitely an option that should be considered if you are looking to buy on a budget!

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