Rear Swing Arm VS Rear Linkage- Mtbr.com
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  1. #1
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    Rear Swing Arm VS Rear Linkage

    So something I noticed and I'd love a good discussion about it. The older DH have a rear swingarm where as the newer DH bikes are all sporting complex linkages. Are there any pros or cons to either. One over the other.

  2. #2
    Now with More Wood
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    There are a number of factors that influence the behavior of rear suspension. The first basic parameter is the leverage ratio - at what rate the movement of the rear axle is translated to movement of the shock shaft. A 3:1 ratio means that for every 3 inches of travel of the rear axle, the shock shaft moves 1 inch (thus compressing the overall shock length by 1 inch). Low-leverage ratio frames try to keep this number closer to 2 than 3....which means that the shock moves MORE for every inch of rear travel (meaning you need a shock with longer stroke on a frame like this). This typically allows for use of lighter springweights, and more oil can be pushed around the shock, which may make it easier to tune, because the behavior is a bit more predictable.

    The second aspect to consider is whether a design is progressive, linear, or degressive. This refers to how the leverage ratio CHANGES throughout the suspension travel. For example, a progressive design means that as you go deeper into the travel, the leverage ratio actually increases. That translates to making it harder to compress the shock the deeper into the travel you get, which is useful for soaking up big hits (to control bottom-out). Note that the SHOCKS THEMSELVES are usually progessive in nature, i.e. it becomes naturally harder to compress it as it goes deeper into its stroke (especially true for airshocks), so sometimes, a linear or even degressive design of the linkage is needed to compensate for the shock's sharp ramp-up at the end of it's stroke (most often found on "AM" or "trail" bikes, to maintain effecient pedalling in the early parts of the travel, and soaking up small-medium sized hits with some comfort).

    The use of linkages allows frame designers more control over the leverage ratio at precise points in the travel. When combined with virtual pivot point suspension (Santa Cruz VPP, Giant Maestro, DW Link, etc), they can also tune in other characteristics (rear wheel path, eliminate or use chaingrowth to control the suspension movement etc). The result can for example be a leverage curve which starts out degressive and finishes progressive (VPP).

    In terms of pros and cons, it is not as simple as that. The pros of the single-pivot non-linkage driven design is simplicity - easy to make, easy to maintain, easy to build stiff. A good combo of frame geo, and a shock tuned for the frame can really bring out a good bike from this simple concept. E.g. Orange, Morewood Izimu, etc.

    Single pivot linkages keep the simplicity of the rear wheel path of the single pivot, and add a linkage to allow for finer control over the leverage ratio throughout the travel. Morewood's Makulu is a good example, widely regarded as one of the best DH bikes available.

    Finally, the more advanced suspension designs can provide benefits like rearward wheel path (less likely to hang up on square edges), a pedalling "sweetspots" that can completely eliminate pedal-bob, etc and so forth. The trade-off being a complex and expensive design, and lots to maintain (and sometimes also tricky to set up). Of course, these are high-performance machines, all you have to do is look at a WC podium, there's usually always a V10 or 2 up there... ;-)

    To sum up - a well-designed bike can be almost as effective regardless of suspension design. The most important aspect is to match and tune the shock to the frame design, with purpose. What type people chose and why is highly subjective...personally I don't like the feeling of multilink suspension, although I've been blown away by how well they pedal even though they remain very supple and active in the rough. I find it easier to jump a simple single pivot, it feels very predictable, even though it can get a bit "skippy" over the rough stuff. I'm no racer, so I don't care about ploughing through stuff.

    My (more than) 2 cents'...sure others will chime in.

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