Feb 10 2009
Single Pivot Suspension
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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!
