Eminent Cycles – The Story Behind AFS

Eminent Launched early in December of 2017. After hundreds of demos, riders have asked us what makes AFS (Active Float System) so unique and what makes our bikes able to impart forward speed and sustain grip the way that they do. The answer to that question has to do with our combination of leverage ratio, anti-squat, floating brake, floating shock, and adherence to good design practices involving pivots and stiffness.  How did we get here and why is the design so special?  To answer that, let’s talk a little bit about suspension, its variables. We'll then discuss our approach and how AFS keeps the tire on the ground for superior traction. 

There are many variables in suspension design that make a suspension perform to the rider’s needs. The right leverage ratio, the right leverage ratio curve shape, anti-squat, anti-rise, pedal kickback, and axle path represent the major factors taken into considerations when developing the suspension for a mountain bike.    

 


Then there are the less calculated subjective elements like frame stiffness, shock brand selection, air volume tuning, compression tuning, rebound tuning, bearing or bushing interaction at pivots/shock interface, that add to the design factors of a bike.    

Put simply, there are as many design variables as there are testing variables that require tuning. Charts only tell half the story and a bike must be ridden to really understand how it can perform. We highly recommend trying our AFS system and other designs for comparison. Get comfortable with what you like as a rider before purchasing your next bike, don't just read articles and look at graphs.  

Ok, now that you have some understanding of the variables that result in the end product feel on the trail, let’s get into it. We're going to focus on a few design variables (since test variables are not so easy to compare) that we consider when creating a bike and how it influences suspension and ultimately, trail traction.   

Understanding The Leverage Ratio Curve

The shape of a leverage ratio curve can tell us a lot about how the shock may feel on the bike.   I don’t think this has been said much, but our opinion is that the leverage ratio should be smooth and progressive so that a natural spring feel can be replicated.  A natural spring gets firmer as it is compressed and we want this on the bike as we go faster and deeper into the travel so it doesn’t bottom out on every bump.  Not only is this important for perceived spring feel, it is equally important for the compression circuit in the shock to not see any up/down changes in the middle of the stroke as this can cause the shock to slow down (due to an oil pressure surge in the compression circuit) and ultimately suspension stiffening and a loss of traction.  In the chart below you will see an example of different leverage ratio curve shapes and what they are called for reference.  At Eminent we first start out with a progressive leverage ratio shape, and set it within the leverage ratio range the we feel will perform best for the intended use.  In the case of the Eminent Onset we have a leverage ration curve between 2.5 and 2.7.  We chose this range because it is low enough to provide ample range of shock tuning and suppleness while still being sufficiently high to provide solid support against rider inputs (pumping and jumping) and support and pop during hard cornering and compressions.

Understanding Anti-Squat

Before we discuss our approach, let’s first define anti-squat so that we are all on the same page. It is commonly understood that with both anti-squat and anti-rise, the measurement is based on a percentage where 100% anti-squat or anti-rise means that the suspension will stay neutral with a person on the bike during pedaling and braking respectively (as a general analysis).   I don’t mean to say they are the same thing, but to say that the scales for measurement are similar.   In this case one will either squat or rise with chain tension or when pedaling and the other would either squat or rise with braking action.  

Specifically in the case of anti-squat, anything above 100% will rise or expand the suspension and anything below will compress the suspension (current practice of 30% above or 10% below is considered to be generally neutral).   For example, the Eminent Onset has 150% anti-squat (see below chart for illustration) at sag so that there is a slight opening of the suspension when pedaling to assist with traction, which we feel is important for any all-mountain or aggressive trail bike that will need to climb steep and rough terrain.    

 

Expanding on the anti-squat discussion, let’s focus on chain tension when the suspension is moving, and how it effects suspension compression when riding over bumps.  If the suspension is opening when hitting a bump during pedaling (if above 100%), the suspension will slightly stiffen if the feet are not allowed to move (not the case where anti-squat is below 100%).   If chain growth is also minimal, the feeling in the feet and suspension is minimal.  If chain growth is larger, pedal kickback (feeling in the feet) and suspension firming are more easily felt.  Taking the Eminent Onset again, chain growth is low and suspension feedback is minimal, so you get the improvement of climbing traction with little drawback.  One last note on this topic, quick engagement free hubs add to the anti-squat/anti-rise equation when coasting as there is less “slack” in the system to account for chain growth during suspension movement and therefore anti-squat & chain growth can have a greater effect.   Finally, keep in mind chain tension changes depending on what gear the bike is in. 

Anti-Rise & Its Effect On Braking

The slang name for anti-rise is “brake jack”, which describes what happens when brake use causes the suspension to stiffen up, resulting in a loss of traction and erratic handling.  We look at the anti-rise curve to better understand this behavior when braking, same scale as anti-squat where 100% is the neutral point.   Anything above is going to compress the suspension and anything below is going to open/extend the suspension.   It is common practice to have anti-rise below 100% as weight transfer during braking is forward and tends to unweight the rear end, so there is not as much of a need to compensate from zero (say towards 100% during braking).  If the anti-rise is above 100%, then there is force pushing to compress the suspension movement  and giving the rider a firming up the feel or brake jack.  Lets take the Eminent Onset as an example, our floating brake enables for lower anti-rise values below 100% (see graph below) which does not compress the suspension, and gives the feel of plush suspension movement for increased traction when braking.    

 

Lastly, from a good design practices standpoint, we decided to: 

  • Mount the shock on the rear triangle “moving parts” (second part of floating system) to reduce off shock or off axis binding (shock flexes together in rear triangle) and improves ease of suspension movement. 
  • Use angular contact bearings to reduce friction in the lateral direction, improve ease of movement, increase durability and stiffness  
  • Move the pivot near seat stay and move it close to rear axle resulting in a long rocker arm for excellent lateral stiffness and immediate shock response to a bump 

If you put all the above elements together, you will find a consistent message: Eminent AFS strives to improve traction and control through optimized suspension movement that goes beyond the typical graphs and takes into account all the variables: the right leverage ratio, the right leverage ratio curve shape, anti-squat, anti-rise, pedal kickback, and axle path.   We invite you to give us a ride and see for yourself at any of our local dealers, demo events or just stop by our corporate office in San Marcos, CA.   

AFS = MORE CONTROL, MORE SPEED, MORE FUN 

 

 

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