Dear MOby,

Say, what’s all this about linkage-type suspensions and non-link-type ones anyway, and what difference does it make? What’s the difference between a progressive spring and a normal one, and what’s all this rising-rate business?

Suspended Disbelief


Dear Suspended,

The Aprilia Shiver pictured above and lots of other bikes use a plain old non-link type suspension, wherein the swingarm is simply connected to the frame via the rear shock absorber. Its main advantage is that it’s simple, lightweight, has no bearings that need lubricating and doesn’t take up much space. On a bike that doesn’t need a lot of wheel travel, it’s perfectly adequate.

A disadvantage, in the Shiver’s case, is that its spring is just as stiff over small bumps as it is over bigger ones, since it’s a “straight-rate” suspension; the suspension doesn’t get stiffer as the rear wheel moves higher in its travel.

Old-fashioned dual shocks like the ones on this Harley Sportster are also “linkageless,” but H-D gets around the lack of a rising rate by winding these particular shocks with progressive springs, which are softer in the first part of wheel travel to soak up small bumps, and stiffer over larger bumps. The first bit of wheel travel mashes the tighter coils at the top of the spring together so there’s no space left between them, called “coil bind.” Once that happens, there are fewer coils to compress, which effectively makes the spring stiffer. Progressively wound springs are a cheap and easy way to achieve a rising-rate suspension, i.e., the further the suspension is compressed the stiffer it gets.

Linkageless suspension works well enough for KTM to use it on most of its motorcycles, including the highly praised Superduke 1290 GT, whose rear end you’re looking at here. It’s harder to see here, but that’s also a progressive spring, and the shock is bolted directly to the swingarm without a linkage. Again, light, simple, few moving parts – and on the Superduke, extremely effective in terms of providing a plush ride that stiffens up when needed.

I don’t remember who came up with the first link-type rear suspension, but just about every current serious sportbike, sport-tourer, and upscale motorcycle uses one. Instead of bolting the shock directly to the swingarm, a linkage system consists of a pair of levers or two, and other parts that connect the shock to the swingarm.

This is the Honda NC700X’s humble linkage seen from below.

Among the advantages of a link suspension is the ability to tune in as much rising rate as you want by switching the lengths and shapes of the components. Through the magical power of leverage, link-type suspensions make it easy to provide a smooth ride over small bumps and a more controlled one over bigger bumps. The shock itself can be smaller, since the linkage can turn not much shock stroke into quite a bit of rear-wheel travel, and it can be tucked out of the way in what might otherwise be wasted space.

Though that wasted space could be on the left side of the bike just as easily, like where Ducati put the V-Twin Panigale’s man tackle.

Freddie Spencer says it was Honda’s Pro-Link suspension on his grand-prix racebike that made him the champ he is today. He may be exaggerating, but who are we to question? You can get as complicated as you want to with all this if you’re the mathematical type; for more detail, Graham Byrnes, PhD, seems to know what he’s talking about.


Send your moto-related questions to AskMOAnything@motorcycle.com If we can’t answer them, we’ll at least do no harm in the time it takes to seek out a believable answer.

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  • JMDGT

    At first glance the linkage system on the Thruxton doesn’t look like it would work at all. Until you get a closer look. I need to ride one.

  • john phyyt

    Also has an effect on damping. Though WP components on KTM have internal rising rates. It seems easier /cheaper but probably heavier to have external rising rate ; yet moto GP bikes have linkages. Set me wondering what does KTM do in it’s moto GP bikes?

    • Old MOron
      • john phyyt

        Eagle eye? . Well spotted.

      • DickRuble

        It’s there..

        • john burns

          I wish I had said that.

          • Buzz

            You just got Rubled!

          • DickRuble

            I am surprised that the SDR-GT is linkless. Are you sure there is no linkage hiding somewhere? The shock doesn’t seem progressive either and I seem to have read the SDR has a linkage.

        • Born to Ride

          In theory, a direct link shock absorber is a two force member due to its linear actuation and articulating pin connections. In practice, those pinned connections aren’t frictionless, nor is the piston/shaft assembly aligned perfectly with the shock body. Furthermore, none of these components are truly rigid and suffer from minute deflections under load. In a free body diagram, you can see that there are vertical and horizontal components to the applied load at the swingarm mounted clevis that cannot be perfectly reacted out internally within the shock. All this being said just to ask, where does the torsion come into play? Assuming that the mounting points of the shock are aligned properly, I’m only seeing bending and buckling failure modes on a direct link shock ala SDR.

          • DickRuble

            It’s the bending. There’s no torsion around the axis of the piston, it’s the torque inducing rotation of the lower mounting point (swingarm) around the upper mounting point that translates into a bending force on the piston and sleeve of the shock.

          • Born to Ride

            Yeah that’s what I thought you meant initially. It was your colloquial use of the term torsion that threw me. I actually drew a FBD because I thought I was missing something basic. Cheers.

  • Joe DeBiasi

    This article is factually flawed. Canting a shock onto a swing arm provides a rising rate in and of itself. ATK and KTM lived off of this for years and Husqvarna and KTM have both resisted linkage suspensions with this justification. Unless a shock is at a percect 90 degree angle to the swingarm the is a rate change during compression. On short travel suspensions a proper canting the right spring and valving work very well.

    • john burns

      Canting the shock does provide a small amount of rising rate, but nothing like a linkage. I wouldn’t say the article is flawed so much as I’d say it doesn’t include everything in 500 words.

      • Joe DeBiasi

        Well no not just a small amount. Gosh I can post the forumulas if need be I was keeping it simple. Length of suspention lengths of the sides of the triangle. The reduction of the lenth of one side and angles at the corners. Its math and engineering. Things that can be right or wrong. AKA the linkage on the 1981 CR Honda Production models. Confused enough to provide a falling rate. My 1981 CR250 is still in the garage thanks to white power shocks and Dwayne Jones that suspension could even be made to work

        • Joe DeBiasi

          Go find a picture of Suzuki’s ” Full Floater linked suspension circa 1981 to 85? 86? It was actually pretty amazing the shock was not directly connected to the frame. The shock was compressed by linkage components at both ends. It was head and shoulders above any other system. Weight and production cost was tagged as its down fall. I always wondered how it would have worked with titanium components or carbon fiber and a modern shock.

          • DickRuble

            That’s good info. There are some Trek bicycles that use the full floating suspension now.

          • Joe DeBiasi

            I’m not Horst Leitner. I raced ATK 250s at dist 37 grand prixs. I like linkage suspension. Well I like things with motors and being out of the mainstream. lol

          • Joe DeBiasi

            A No-prize if you know who I was Mr. Leitner is

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      • Andrew Horton

        There lives the devil. If its impossible to to dispel misconceptions about a subject in 500 words why publish the 500 words at all? The Shiver, like the old Yamaha monocross system or the even older version that Vincent pioneered has a progressive rate engineered in because of the extreme canting of the shock. Some early twin shock bikes like Velocettes had adjustable top mounts allowing the “dialling-in” of progression via variable canting of the shocks Many earlier linkage systems were actually regressive not progressive in an attempt to provide some subtly to the rear wheel damping curves under higher load, usually mid corner high lean angles. These days with improved damper design most linkages are either 1:1 or slightly progressive.

        • john burns

          Because it’s what we get paid to do? Ask MO is intended usually as a basic primer on these kinds of subjects, a starting place. According to this old road test of the YZ250J, it was adding linkage to the original Monocross that MADE it a rising rate system, or at least much moreso than the original. http://davestestsandarticles.weebly.com/uploads/4/8/4/5/4845046/h.pdf