Nerding Out: Do Kinematic Graphs Really Describe Suspension Performance?

Recently I spotted this intriguing comment in Alicia Leggett’s recent Revel Rail review.

The techniques that have been developed to measure how active the suspension is on a bicycle – anti-squat and anti-rise – appear to be fairly unremarkable when it comes to this design. If they don’t tell the full story, what measurements do we have that do? How do two bikes with the same leverage curve have different suspension forces, all other things being equal?

The Rail’s anti-squat and leverage curves don’t look very different to many other modern bikes, so does that mean the suspension won’t perform any differently?

This topic is something I’ve been thinking about a lot ever since I reviewed the Marin Wolf Ridge 9 back in 2018. That bike is one of three I’ve since tested using Naild’s R3act suspension system, which features a sliding suspension component in combination with links. The marketing claims implied that it worked in a fundamentally different way to other designs, allowing it to take all the best characteristics of other systems with none of the downsides. Information on how it did this was nonexistent (and I did ask, a lot), but I was told not to worry about the kinematic graphs because Naild’s system worked in a different way to other bikes, so its true brilliance couldn’t be explained using the usual methods.

By the way, if you’re wondering what terms like “anti-squat” and “leverage curve” even mean, I recommend Dan Roberts’ articles on the topic here and here.

In reality, the Naild system operated in the same plane of physical constraints as any other suspension system. It’s essentially a four-bar suspension layout, except it uses a slider in place of one of the link pivots, so the usual tools (anti-squat, anti-rise, leverage ratio, etc…) explain how it operates about as well as any other bike. As you can see in this article, it was tuned toward high anti-squat and high pedal-kickback compared to most other bikes, and that’s no bad thing as it made it pedal very efficacy despite a lightly-damped shock, but there were drawbacks to this.

So, I would be very skeptical of any brand telling you that their layout – no matter how many links, sliders or flippy-spinny bits it has – is so revolutionary that has benefits that can’t be seen on any kinematic graphs, or that they manage to side-step the usual compromises. Suspension is all about compromises.

But to answer the core of the question, do these graphs tell the whole story of how the suspension works? Absolutely not.

Firstly, there’s a lot more to unpack in these wiggly lines than is sometimes made out. People often quote a single number – such as the percentage anti-squat at sag, or the change in leverage ratio between the start and end of the travel – as if it tells the whole story, but there’s a lot more to it than that. For example, the gradient of the anti-squat curve may affect how firm the suspension feels under power, or the shape of the leverage curve as it wiggles between the start and end points may be more important than the leverage numbers at those two points.

Another caveat that’s often forgotten is that anti-squat and anti-rise depend on the center of gravity position of the bike and rider, so if you’re comparing anti-squat curves between two different bikes, they aren’t directly compared to both are calculated with the same set of assumptions for the COG position. The frame size, chainring and sprocket selection also have to be the same to make things fair. But with all of those caveats and subtleties out the way, the kinematic graphs do describe the suspension linkage very well.

But how the suspension behaves and how the bike actually rides depends on much more than the frame linkage. The choice of shock and its damping tune are arguably more important still – in the case of that Marin Wolf Ridge, the light damping tune is probably the main reason the suspension performance was so unusual and opinion-dividing, not the slider. Meanwhile, the geometry, wheel size and componentry can also affect how much harshness is transmitted to the rider. All these factors and more interact with one another in a way that’s too complicated to put into any graph. That, I hope, means we bike reviewers will still have a job for the forseeable future.


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