Sine Suspension

SINE SUSPENSION SYSTEM

We have developed our patented SINE suspension system with the characteristics and kinematics to best counteract the effects of weight transfer on the suspension system, eliminating bobbing from pedaling, while retaining the maximum tune-ability for riders of various sizes, proportions and ride feel preferences, to get the optimum suspension performance from their Arktos whether that's in terms of sag/negative stroke suppleness, mid-stroke stability and playfulness, or end-stroke/big-impact absorption. 
Wait, what does that mean? Well, if you like, settle in for the longer explanation, and a bit of history:


That some of the earliest bicycle designs of the mid 1800s were called bone-shakers was no joke. Forget about suspension. Solid tires, inflexible construction materials, and un-tensioned wheel designs all made for a harsh ride and the well-earned bone-shaker nickname. But they did one critical thing: they effectively decoupled the relationship between forward movement and the acceleration/deceleration inherent in humans walking motion, enabling more efficient use of energy, higher speeds, coasting, and that glorious wind-in-your-hair feeling that we all love. 


It's for those benefits of the design that the bicycle was even able to catch on in popularity, even as the harsh ride feel launched a search for comfort and performance through suspension design that has spanned more than a century, and continues today. In that time span, we've seen designs suspending the rider, and that suspend the bike. Designs at the saddle, handlebar, stems, rims, spokes, hubs, and elsewhere, integrated into the frame and integrated into the fork. Attempts at all of these have drifted in and out of favor, and to some degree were made less necessary for road riding and transportation cycling by the compliance of pneumatic tires, tensioned-spoke wheels, and advances in frame and component materials. 


But then, mountain biking happened, unleashing an era of suspension development like never before seen in cycling: one that drew designs from more advanced machinery like motorcycles and automobiles, and even airplanes, as well as from past bicycle suspension designs.  


As designers worked on mountain-bike-specific suspension solutions and adapted designs from other markets, though, they were consistently confronted with three very bicycle-specific challenges: Within the system of bicycle and rider, the rider's weight is a much more significant factor than it is in the context of heavier, motorized vehicles. A bicycle's external, multi-geared drivetrain system provides significantly varying inputs to suspension systems, compared to gearbox-type transmissions. And, even as the bicycle allows more efficient and smoother forward progress than walking or running, humans still deliver inconsistently applied power to the bike throughout the pedal stroke, with peak power around 9/3 o'clock pedal positions, and dead spots at 12/6 o'clock. 
Taken together, the challenges and opportunities that those dynamics represent primarily relate to the two most important elements that suspension engineers try to balance in order to address them: squat, and anti-squat. 


With motorized vehicles, when you open the throttle or stomp on the gas pedal, the weight of the vehicle shifts significantly rearward, compressing the rear suspension as the front end lightens up and rises. As the vehicle reaches whatever operating speed you've chosen, and acceleration subsides, weight returns to a more neutral position. (And of course, if you stomp on the brakes, we see the opposite effect. Weight shifts forward, compressing the front suspension, and reducing weight on the rear of the vehicle.)


On a motorized vehicle, the engine and transmission smoothly and consistently apply power, so we can consider squat (rear suspension compression) in broad terms. With a bicycle, because the power input is inconsistent, we see varying amounts of squat not just throughout an overall acceleration to a certain speed, but also within each pedal stroke. This is what, if left unmanaged, can lead to that terrible bobbing feeling that we all hate, as the suspension loads and unloads with each pedal stroke, leaving the rider uncomfortably bouncing down the trail. 
There are a number of ways that bike designers have mitigated this bobbing cycle. Think about suspension systems that have lever-activated or automated lockout systems, or lots of damping, or just lots of low-speed compression damping. Designs with high levels of inherent friction, or that are intended to be set with no sag. 


What we believe is that the best way to mitigate bobbing is to design a suspension system through which drivetrain forces oppose weight-transfer (squat) in just the right amounts, at just the right points in a suspension design's travel. Naturally, these drivetrain forces are called anti-squat. Mostly, this is because it is an obvious name for something that opposes squat. But also it is because it was named by engineers, not marketers. That's probably for the best. But we digress. 
Taking that one step farther, we see short, dual-link suspension (SDL) designs as the format that give engineers the best ability to manage squat/anti-squat throughout the suspension travel, while also addressing the other requirements of building a bicycle, in terms of dimensions and geometry and component fit, and other factors. 


The other side of that coin is that SDL designs can be very sensitive to the slightest variations in pivot point positioning. Some of the earliest SDL designs were very successful in managing squat/anti-squat, which is a big part of what led to their success in the marketplace. But they were also unlikely to offer a consistent experience from one frame to the next, even within the same brand, model, and size, owing to the effects of basic manufacturing tolerances on pivot location. And while these designs were very good at holding the suspension stable at the suspension sag point under pedaling forces, they also kind of tended to stay at that point in the travel, offering somewhat muted suspension performance, and a ride quality that never really felt balanced with the front suspension. 


But the best suspension designs always come with refinement. Across manufacturers, riders have often seen that a well-refined design (even one that offers engineers less anti-squat tuning capability) often outperforms a new design touted as being technically superior. Our approach is to pursue the refinement and optimization of what we see as the best, most tunable design: short dual link suspension/SDL. To that end, much has been made of whether SDL links co-rotate or counter-rotate and probably some other stuff, but the bottom line is: Do they achieve the requisite anti-squat characteristics, within the desired frame size, shape and structural characteristics, while producing suspension that is tunable to also deliver the best ride performance for small and large impacts, and for riders of different sizes and shapes? 

sine-suspension-mountain-bikes
And that's really where the current design evolution is at, and what defines one of our biggest goals for the SINE suspension design: We've done everything in our ability to deliver a suspension system that addresses suspension performance and anti-squat characteristics as best as possible for the widest range of riders on a given size bike, while accounting for the forces imparted through modern drivetrain configurations. Because the reality is that a rider who is 5'10" and 190lbs, riding a medium bike is potentially going to be in a much different position, and generating much different forces than a rider who is 5'10" and 150lbs. Their stem length and saddle positions may be totally different, based on body proportions. Their upper vs lower body weight distribution may be totally different. And all of this affects their center of mass, which is what affects suspension movement. 


With these rider size, shape and position preference differences in mind, we've endeavored to build the SDL bike that leaves the most additional room for tuning by shock manufacturers and riders, extending the most customizable, high-quality suspension performance to the most riders we can. That's the philosophy and capability built into every Alchemy Arktos. 

 

KINEMATICS

So, let’s start with how Sine works. As the bike moves through the travel, the rear wheel path resembles a mathematical Sine curve. At the beginning of stroke, you see suspension regression in order to allow the bike to absorb small bumps and provide climbing traction. As you move into the middle of stroke the suspension moves into a progressive shock rate. This prevents wallowing on big hits or in hard and fast corners.

When you really push it and open the end of the stroke, the suspension becomes regressive again to enable full use of the rear wheel travel. This pattern is specifically designed to minimize chainstay growth, improve pedaling efficiency and keep the suspension active under braking. All these factors make for an incredibly lively and efficient ride.

HOW TO PERFECT YOUR OWN SINE SUSPENSION

The Sine Suspension system is optimized for use at 30% overall sag. However, personal preference and riding conditions can influence the amount of sag desired. We encourage you to mix it up and experiment to find what works best for you. The “sag” is the amount of travel the shock uses under normal rider weight. An ideal suspension sag will optimize the three areas of travel: negative, mid-range, and deep travel. You’ll know you’ve perfected the sag when you experience a plush, small bump feeling in your negative travel, a firm and lively feeling in your mid-range travel, and a ramping and bottomless feeling in you end travel.

HOW TO CHECK SAG

  1. Gear up head to toe so you start with an accurate rider weight.
  2. With someone holding the bike, stand on the pedals and get in your normal riding position on the bike.
  3. Bounce up and down on the bike, compressing the rear end of the bike and the rear shock; when you are steady again, have someone push the travel ring up the shock against the wiper seal.
  4. Dismount the bike gently (so as to not move the travel ring).
  5. Check your shock. The amount of stanchion shown between the wiper and travel ring is your sag. (30% sag would show 21mm of exposed stanchion between the wiper and travel ring.)
  6. If there is less than 30% sag, remove the valve cap and let out some air with a shock pump. If there is more than 30% sag, add more air. A good starting point is to pump your rear shock PSI to your rider weight and work from there: 180 lbs=180 PSI.
  7. Once you are dialed put the cap back on and you are ready to go ride some trails.
  8. Use the Tuning Guides to really dial in your suspension

Still not sure if you’ve got your Sine Suspension up properly? – Contact us at hello@alchemybikes.com or visit our Colorado Workshop and we can help you find your perfect settings.

 

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