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I've been looking at full-suspension mountain and trail bikes lately, and I've noticed that the rear shock can come in a few different configurations:

  • It can be installed roughly vertically, between the seatstay and the downtube. E.g. Norco Range A7.2.

  • It can be installed nearly horizontally, also between the seatstay and downtube. E.g. Diamondback Atroz Comp.

  • Finally, it can be installed between the seatstay and the downtube. E.g. Norco Revolver 9XX.

What are the effects of these different configurations, and why does it seem like that last configuration is so much more expensive (on average) than the other two?

  • Hopefully someone will provide some insanely detailed answer, but their are an absolute plethora of different rear suspension setups. Knucklbox (diamondback), DW link (pivots) . I can't speak for the pricing but some of the differences are center of gravity, peddle bob, etc i feel like this is one of those things that will come down to personal preference but i look forward to the answers. – Nate W Apr 6 '16 at 15:27
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    One word summary of the practical differences - "Patents" – mattnz Apr 6 '16 at 20:16
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The good folks at Bike Radar have already covered this in pretty good detail in a two part article: Part 1 and Part 2

There's also a chunky thread on the Pinkbike forums that has pictures and descriptions of loads of different setups: Pinkbike - Basic Full Suspension Types / Reference With Pictures

In regards to price, it is not the suspension setup making the difference, it is the quality of the components.

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    Could you expand this to include a summary of the contents of the links? (Although I do understand a summary of squishy geometry is an oxymoron) – mattnz Apr 6 '16 at 20:16
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I would say that the position of the shock doesn't really matter.

What matter is :

  • The path of the wheel axis
  • The shock dynamic (How the shock is compressed regarding the position of wheel)

1) The path of the wheel axis

If the path is circular then the braking force will bend the suspension. If the center of this circle is lower than the front of chain (where the force comes from), then the force of pedaling will also bend the suspension (added to the weight of rider). This is called "pumping". To circumvent these problems the engineers have :

  • rised pivot point above chain, so the force of chain counter the weight of rider. This was the first solution. It is found today on cheaper bikes as it just require to move pivot upper, this does nothing against brake force.
  • virtual pivot point and linear path. This is more expensive as it need more pivots working together. My favorite design (from engineer point of view) is parallelogram design that you could find on Giant Trance for example. The rear is a full triangle connected to front part with two links. (look on close ups from left side, just above pedal axis, you'll see that second link).

2) The dynamic of shock

A metallic spring has a linear strength each time you apply one unit of mass, you get one unit of movement (approx). This is good for the suspension. But metallic spring weights a lot. Air springs are lighter but they are not linear, the more you compress them, the harder they get. To circumvent this engineers use levers and play with angles (virtual pivot point).

Lot of designs are mechanically equivalent. With levers you can place shock where you want, but some places makes more sense as they apply forces where it is easier for the frame to bear them. The goal of the game is to get a good behaviour, fewer pieces, less weight, better reliability and strength, and not infringe a competitor patent. In the end, the actual position of the shock is as much a question of patent and look than real mechanic.

Please feel free to rewrite this answer as my english is far from perfect. It would be also better to explain forces with schemas.

  • I'd also value where the failure modes are "safer". IE a bike that would fall down if one element of the suspension broke, is less appealing than something with resilience or redundancy built in. I don't want my backside suddenly on the backwheel if the suspension breaks! – Criggie Apr 8 '16 at 4:23

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