The Tuesday Tune Ep 12 - Leverage Rates

Mountain bike frames have various forms of what we broadly refer to as suspension design, but more specifically could be termed kinematic design. Kinematic design refers to the ways which each member of the suspension linkage move, particularly relative to one another. In other words, the suspension kinematics are the geometric motions of the linkage, before we start introducing force or mass to our considerations.
Anyone who's ridden more than a couple of different mountain bikes is well aware of how different the rear end of the bike can feel, even with the same travel and when using the same shock. Variations in leverage rate, among other things, are a very large factor in determining how the suspension performs, so this week in the Vorsprung Suspension workshop, we're looking at the ways in which variations in the leverage ratio can affect the feel of the bike, and why small changes can result in fairly large differences.
Leverage ratio is typically defined as the ratio of mechanical advantage that the axle has over the shock. This can be an instantaneous leverage ratio at a single point in the travel, or an average leverage ratio obtained by dividing wheel travel by shock stroke. Plotting the instantaneous leverage ratio against travel gives us a leverage rate curve. The difference between ratio and rate is that the rate describes how the ratio is changing throughout the travel. In the motorsports world it is more common to use the term motion ratio, which is the same thing but inverse - it is obtained by dividing shock stroke by wheel travel.
When considering the overall wheel rates - that is, the spring rate and the damping rate when measured at the wheel - it is necessary to understand the spring and damping characteristics of your shock as well as the leverage rate characteristic of your linkage. Some frames work really well with the linearity of coil shocks and relatively poorly with progressive air shocks, and vice versa, and it is this interaction between the leverage rate and the shock's spring characteristics that is primarily responsible for this. An in-depth discussion of how air springs, particularly those of our own products, interact with various leverage rate curves can be found here.
Please note a few things here:
1. As usual, the devil is absolutely in the details. Generalisations, including some of the things we refer to in the video, are not applicable to every variant of any particular linkage design, and this is a long long way from being a comprehensive breakdown of leverage rates.
2. A certain acronym or name for a linkage type does not mean all frames of that type perform or feel the same. They can vary hugely.
3. We're not here to tell you what system is "best". There is really no objective way to assess that - everyone's preferences and priorities vary, and what works well for someone who likes a super firm feel doesn't necessarily work well for someone who wants the plushest thing out there.
4. If you'd like to see what your own bike's leverage rate is like, download a program called Linkage and measure up your own bike to see how it stacks up. Note on using this program: there are a great many existing files out there and a lot of them are a fair way off the mark, particularly on bikes with very short links. Don't rely on clicking on points on a photo for accurate inputs - that can be accurate enough for singlepivot bikes with no linkage, but on anything else it's more than likely going to be misleading. Use a measuring tape to verify distances between points on your suspension if you want accurate results.
Terminology worth knowing:
Linear leverage rate: this would be better termed "constant leverage ratio", as this is what delivers a linear force vs displacement curve at the wheel (if using a linear spring).
Progressive leverage rate: also known as a "rising rate", this creates a force vs displacement curve at the wheel that is progressive, ie an increasing wheel spring rate even if using a linear spring.
Digressive leverage rate: the opposite of the progressive leverage rate.

[@NerfHerdsman]

Great video

[@evilbikerider]

Make more videos Steve I've never learned so much about suspension got a new full suspension and for once didn't feel overwhelmed set it up from what I've learned and my bikes never felt so good!

[@alejandrotejedo853]

I travel race to race. Listening on my phone the audio is not easy. Thanks for the effort.

[@alfrednOObel2]

In the intro you say that we don't care about the leverage ratio in terms of shock doing the work, but doesin't it affect how rebound works? If the leverage ratio is higher, the rebound will be weaker, so I suspect that it will not be as fast as with lower ratios. Am I figuring it out right?

[@dad_bod_racing]

Hi Steve, can you do another video on leverage rate and it's effect for either heavy (>110kg) or light (

[@shayburton4139]

Would like to ask a couple of questions relating to the leverage ratio video concerning a 2016 gt sanction 1 is this bike considered to be a single pivot ? 2 how would I go about measuring the Swingarm to shock eyelet to find the leverage rate/ ratio on this bike 3 and how would said measurement be interpreted to the rest of the leverage rate/ ratio Trying to find out what type of shock would work best with this bike and what to avoid, been trying to work this out myself bur can't seem to find enough information, standard shock is fox float x evol 215x63. thanks

[@badazgamaz]

Hi ! Very interesting vidéo ! Would you concider the 2016 specialized enduro as linear ? Witch could mean that an air shock is a better choice than a coil one ?

[@upanddownhills]

If a bike has a linear curve, would it make more sense to have an air shock so that you have an element of control over what the curve is doing, or would a coil shock be better? Im guessing personal preference has a large part to play in this as well?

[@alfonsozepeda1]

Where can i find the leverage ratio of bikes nowadays? there is no information ( or easily obtainable ) from bikes companies

[@abelramos8652]

Hi Steve! One question ... what would be difference between a 2 to 3 LR vs a 2.5 to 3.5 ? Sorry if you explain in the video i can read and write engish but earing is more difficult to me. Thanks

[@softbatch7236]

When the shock and leverage rates are added what are the normal desired force curves at the wheel? Is there an ideal curve that manufacturers try to hit?

[@VorsprungSuspension]

Every manufacturer seems to have a different idea of what is ideal - to the point where some of the leverage rate curves are literally the exact opposite (inverse) of one another. There is not a particularly strong consensus on what works best. I think aiming for a generally progressive wheel spring curve is the most widely-agreed-upon characteristic, but even then there are some extremely popular bikes that go the other way.

[@stevenmichaelis]

At first I thought you might have been making a mistake, but now I see the language is just a bit confusing (to me). For a Progressive leverage geometry, as the rate rises it drops on the chart, indicating a decreasing wheel-to-shock travel ratio, requiring LESS spring force per mm of wheel travel. For a Digressive leverage geometry, as the rate decreases it raises on the chart, indicating an increasing wheel-to-shock ratio, and thus requiring MORE spring force per mm of wheel travel. That makes perfect sense! But it is a bit confusing.

[@VorsprungSuspension]

Yes, it's more intuitively understood when using motion ratios rather than leverage ratios (the two are the same thing, but motion ratio is the inverse of leverage ratio). Basically the spring rate increases at the wheel throughout the travel in a progressive system.

[@drejec1]

How do you calculate the progression of the linkage in %?

[@andrewaustin7870]

I also would like to know this. Vorsprung please comment

[@greggie111]

Does that mean the best shock for a VPP bike is a coil shock? What about all the SC bikes with air shocks? Good for pedaling but hard to use all the travel?

[@VorsprungSuspension]

Not necessarily. Leverage ratio has almost no influence on pedaling performance, that is to do with anti-squat. VPP bikes can be more up one end or the other of that curve as well, not all of them ramp up significantly at the end of the stroke, and not all of them are substantially falling rate at the beginning (eg the 951... which ramps up MASSIVELY but has almost no falling rate early on). The specific details ALWAYS matter.

[@W1RELE55]

Would you think coil would be suitable, specifically, for the Hightower which has regressive/linear/progressive curve I believe? If the end stroke is only slightly progressive would you run less sag at the expense (perhaps?) of suppleness at the start of the stroke?