CBF™ Suspension – Patent Number US 9,O61,729
Canfield Bikes has been refining the parallel-link suspension since the late ’90s when the first Canfield prototype was brought to life based on the trailing arm suspensions of trophy trucks; no one else in the industry has as much experience with this design. It was refined into the terrain-flattening rearward-travel downhill performance that makes the Jedi so unique today. But Lance and Chris Canfield knew that was only the beginning.
Finding the Balance between smooth, active suspension travel and a firm, efficient pedaling platform has been somewhat of a holy grail for bicycle manufacturers and suspension gurus. Engineers and design teams have spent years attempting to maximize these traits while maintaining favorable geometry, durability and ride quality.
There are a number excellent suspension designs available on mountain bikes today, but most make sacrifices on one end of the spectrum or the other. The same “efficient” design gives up pedaling efficiency when incorporated on a downhill bike, and will sacrifice small bump performance when applied to a cross-country bike. What’s more, those characteristics can fluctuate wildly on the same bike throughout its travel.
But what if there was a way to maximize these characteristics without sacrifice?
Enter, the patented Canfield Balance Formula.
It was in 2009 that Lance and Chris Canfield locked on to the potential of designing around the Center of Curvature (link to glossary). They saw so much potential in this intangible point in suspension kinematics, they referred to it internally as the “God Spot.”
By going back to the drawing board, dissecting suspension kinematics and focusing on a universal formula rather than a specific suspension design, Canfield Bikes has been able to create a patented formula that provides optimum anti-squat throughout the entire range of travel, resulting in the most efficient pedaling possible, regardless of factors like sag, and without sacrificing bump compliance or traction, and with no unwanted pedal feedback from braking or drivetrain forces.
The Canfield Balance Formula™ has been carefully refined and patented over the nearly a decade, and the result is one of the most active and efficient platforms available on mountain bikes today.
How did we do it?
Because the Instant Center fluctuates so much on most multi-link bikes, there is a very small sweet spot where the bike pedals efficiently. This is the reason most suspension designs have a recommended sag setting.
This is in part because the IC is the focal point in configuring most suspension designs. In the grand mechanical scheme of things, mountain bike suspension is relatively new technology. Certain truths and methodology—such as designing around the IC—came from existing designs, such as motorcycles and other chain-driven suspension vehicles. We can all agree that there are a lot of similarities between mountain bikes and motorcycles, but there is one very big difference: the motor.
We humans make very sloppy and inconsistent motors. Our power delivery is far from smooth and constant, especially over the kind of terrain we typically encounter on mountain bikes.
The IC is a key piece of the puzzle, but there is another very important yet often overlooked part of the equation.
In multi-link bikes, the IC constantly changes for any given point in suspension travel, and the rear wheel is no longer rotating on a perfect arc like a single pivot. But if you were to connect that rear axle’s location at any point on its path with that ever-changing IC, the area where all those lines intersect for the entire range of travel would be the Center of Curvature (link to glossary). This is the “virtual pivot point” around which the rear wheel actually rotates (On most bikes, it’s a fairly large area). On most multilink bikes, the CC changes location as the rear wheel moves through travel, sometimes over an area as large as several square feet.
Versatile. Smooth. Efficient.
The CC serves as a tipping point in the balance of drivetrain and suspension forces and there’s a very small sweet spot in the bike’s travel where optimal pedaling and suspension characteristics are present.
So what if we took what we know about suspension, and Balanced it with the drivetrain forces created by this inconsistent human motor?
The patented Canfield Balance Formula focuses the CC precisely in a very finite area on the chainline/top of the chainring, pointing the pedaling forces directly into the IC throughout the entire range of travel, creating the most efficient yet active pedaling platform possible, completely independent of sag, travel and both drivetrain and braking forces.
1: THE MOST EFFICIENT PEDALING AND POWER TRANSFER POSSIBLE
CBF™ points the chainline and drive forces directly into the IC throughout 100-percent of the travel by balancing the CC over the chainring, resulting in maximum pedaling efficiency, regardless of where you are in the travel, what terrain you are on or what kind of power you’re putting down. All the power you put into the pedals propels you one direction–forward—allowing the suspension to do its job completely independent of drivetrain and braking forces.
2: COMPLETE SEPARATION OF DRIVETRAIN AND SUSPENSION FORCES
By Balancing the CC on the chainline, CBF™ creates an IC that can travel from a high position to low, forward to back, mirroring the rear axle and keeping the distance between the two more consistent, lessening chain-growth/pedal-kick throughout the travel. As the wheel moves up, the IC moves down, avoiding unnecessary interruptions to the pedal stroke. The chainline pivots with the suspension, around the same point, providing complete isolation of drivetrain and suspension forces for an incredibly smooth ride.
3: SMOOTH, ACTIVE, CONTROLLED BRAKING
CBF™ decouples suspension and braking forces, allowing the rear wheel to smoothly and efficiently track terrain even under hard braking for maximum traction and control. “Brake jack” is virtually non-existent. CBF has optimal anti-rise (80%-100%) throughout travel, preventing braking forces from causing unwanted squat or rise, maintaining favorable geometry and allowing the suspension to do its job, keeping the rider in control when it often matters most.
4: NOT SAG DEPENDENT
CBF™ is not sag dependent. Our formula allows the rider to set up the sag position anywhere in the travel with maximum anti-squat and pedaling efficiency. Because the chainline always points at the IC, there is no way to miss the “sweet spot” in the travel. Of course, your sag and suspension setup will still affect bump compliance and how much travel you use, but if you like to run it soft or it has not been properly set up, you won’t be giving up any pedaling efficiency. You will also maintain efficiency when climbing (a situation in which weight is shifted rearward, causing the bike to sit deeper into travel beyond the normal ideal sag position), riding downhill, through obstacles and rough terrain, or any other variables that require efficient pedaling deeper in travel.
Let’s take a look at some common suspension designs, as well as their pros and cons.
SINGLE PIVOT DESIGNS
On a single pivot, the placement of that pivot greatly affects the way the suspension performs. This is a good basis for understanding how other factors will effect a more complicated multi-link design.
The lower the pivot placement, the more the bike tends to squat .
Pros: Suspension is more active and smoother pedaling in rough terrain. As you pedal and compress the suspension, bumps are more easily absorbed when the tire impacts it resulting in a more compliant ride and better traction.
Cons: This is generally tiring and inefficient. With each pedal stroke, the chain is pulling the suspension into the shock, using your power to compress the suspension rather than propel you forward.
The higher the pivot placement, the more the bike tends to exhibit anti-squat .
Pros: More anti-squat results in efficient pedaling. The bike acts more or less like hardtail, transferring more power from pedaling forces into propelling the rider forward rather than being absorbed by the suspension.
Cons: While it makes pedaling more efficient, it also stiffens suspension over rough terrain, detracting from small bump compliance. This results in a loss of traction, and for riders on flat pedals, increases the chance of slipping a pedal in technical terrain. Too much anti-squat can also result in a loss of power by extending the suspension and raising the rider rather than propelling him/her forward.
Aligned pivot placement occurs in single-pivot frames that align the pivot with the chainline (this is the line of the chain over the top of the chainring through which pedaling forces are directed).
Pros: This results in a very “neutral” suspension that balances these forces for an optimal mix of pedaling efficiency, traction and bump compliance.
Cons: This “neutral” alignment only occurs within an ideal sag range. As the bike cycles through the suspension travel, the characteristics associated with high and low placement affect performance.
Modern multi-link bikes typically connect the front triangle to the rear with four pivots on two links (two pivots per link). If you were to draw an imaginary line forward through the two pivots on each link until they intersect, you would find an intangible point called the Instant Center. But unlike a single pivot, the IC moves around as the suspension cycles through its travel.
The IC is also called the instantaneous center of zero velocity, because it acts as the point where the system is balanced. If the chainline forces we discussed earlier are aimed below this point, it will pull up on the suspension while pedaling (squat), much like a low single pivot. If the chainline forces are aimed above, it will pull down more (anti-squat), much like a high single pivot.
In order to achieve favorable pedaling characteristics on a multi-link bike, a suspension engineer will line up the chainline (force line) with the IC at the recommended sag point. This is why proper sag setting is important in most suspension designs.
The “Balancing Act” of Multi-Link Suspension
The way most designs are laid out, the chainline points into the IC only when the bike is properly sagged in a very specific range (usually 25 to 35 percent).
This results in a balanced and efficient pedaling suspension platform when the bike is in the small window of perfect sag position. If the sag is too HIGH or too LOW, missing this ideal sag position can lead to the chainline pointing too high above the IC or too low, resulting in inefficient and/or inactive suspension.
The ideal sag setting doesn’t account for the fact that, as mountain bikers, we very rarely remain in that exact percentage of sag while actually riding our bikes. Due to the variety of terrain we encounter, out of saddle efforts and technical maneuvers, suspension typically fluctuates from about 20 to 45 percent of travel even while pedaling and climbing.
Because the IC is constantly in flux throughout travel, most multi-link designs are an exercise in compromise, sacrificing certain areas of performance for others.
Pedaling through bumps, up and down hills, and through the wide variety of conditions encountered while mountain biking means that for a truly efficient and active suspension, we need optimal performance throughout the entire range of travel. Enter, the Canfield Balance Formula™.
Glossary of Terms
Let’s take a closer look at a few of the factors affecting the way mountain bike suspension performs.
Sag: The percentage of suspension travel compressed by the rider’s weight in a static riding position. Normal rear suspension sag recommendations are 25 to 33 percent, depending on design.
Squat: The force generated when the rider pedals forward must overcome the inertia of the mass of the rider and bike. Invariably, some of this force is displaced through compression of the suspension, essentially resulting in a loss of forward motion, and as most understand it, efficiency. The drive forces pull up on the swing arm, pulling the rider down. This manifests as what is more commonly known as suspension “bob,” or seemingly “over squishy” suspension while pedaling. Squat is common with low single pivot bikes.
Anti-Squat: When certain variables are in place (we’ll get to those in a minute), the increased chain tension resulting from pedaling forces pulls down on the swing arm, extending the suspension, combating the aforementioned “squat.” It’s easy to see why this is generally considered a good thing when it comes to pedaling efficiency. However, too much anti-squat (we’ll say more than 100 percent) can not only make a suspension overly firm, but actually waste power by lifting the rider up rather than propelling him/her forward. The rider is pressing down on the bike and the bike with 100 percent anti-squat will push back the exact same amount, canceling out any motion. Anti-Squat is common with a high single pivot bikes.
Rise: Commonly referred to as “brake jack,” rise occurs when rear braking forces are at odds with the riders forward momentum and the result is stiffening and extension of the rear suspension. This results in two negatives: The rear wheel loses traction and skips over the ground, and with the rise of the suspension, the rider’s weight is transferred forward and over the front wheel while steepening the geometry. Rise is common with high single pivot bikes.
Anti-Rise: Also known as “brake squat,” anti-rise occurs when the rear suspension compresses or “squats” into its travel while braking. This is more favorable than rise because it slackens and lowers the geometry and keeps the rider’s weight back which is more stable when going downhill, however too much anti-rise can result in a less active suspension and loss of traction. However, on the back of the bike during braking you want the bike to squat slightly to counter the rider's mass shifting forward dramatically during braking. 100 percent anti-rise would feel like too much. Anti-Rise is common on low single pivot bikes.
Pedal Kick: As the rear axle moves throughout travel, its distance in relation to the bottom bracket changes. If this changes too dramatically in any one direction, especially rearward, chain “growth” results, tugging the chain and in turn the cranks back so that the pedals “kick” back as well. In other words, the forces are translated the opposite direction, from the suspension through the drivetrain to the rider, resulting in unwanted pedal movement. I think we can all agree that this is a negative. Pedal kick is common with high single pivot bikes.
Instant Center: Many modern designs—and patents—focus on the Instant Center because as long as drive forces are pointed into the IC, the suspension is balanced. The trouble is that when the IC moves through its path during travel, it will only line up with the chainline once —in other words, it’s very sag dependent. That’s why proper sag is so important. And also why you’re going to give up some pedaling efficiency if you like to run your suspension a bit softer (more sag) for better bump compliance and downhill performance.
Finding the IC – The instant center (IC) is an intangible point found by drawing an imaginary line forward through the two pivots on each link until they intersect. This does not move during compression on a classic single pivot design because it is the pivot. On modern multi-link designs, it constantly changes location as the suspension cycles through its travel.
Center of Curvature: The Center of Curvature is the virtual pivot in multi-link designs.
Finding the CC – As the rear suspension compresses, the rear axle moves along a given path, or arc, relative to the IC. Of course with different suspensions, this path varies greatly and even changes direction throughout travel. But if you were to connect any single point along the rear wheel’s arc path of a multi-link bike to the aforementioned IC with a straight line perpendicular to each point, and overlayed all those lines for any given point in the travel, the area in which those lines intersect is referred to as the Center of Curvature; the intersection of those two constantly changing points. Though on most multi-link designs, that’s a fairly large area, as the CC is constantly migrating, like the IC.
The CC has largely been overlooked as more of a byproduct in suspension design, rather than a focal point—until now.