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Niner Bikes designed their proprietary CVA suspension system in 2008 and it was granted a US Patent in May 2011. In 2012, the system was awarded a Eurobike Design and Innovation Award. Over the years since, it has continued to earn positive reviews from riders, testers, and athletes around the world.
In a world of ever-evolving trail bikes, the staying power of this design is impressive. CVA is still used across Niner’s entire mountain bike range, from the cross-country oriented RKT 9 RDO to the newly redesigned RIP 9 RDO.
It turns out that the tunability of CVA suspension has kept it relevant as the sport and bike designs have changed over time.
What is CVA?
Niner’s Constantly Varying Arc, or CVA™, suspension design is a short dual-link, four-bar system unique to Niner. Originally designed in the early days of 29ers, specifically to account for the greater bottom bracket drop on these bikes, the CVA pivot and linkage layout is ideal for the range of larger wheel and tire sizes found on all modern trail bikes, including 29er, 27.5+, and new school, wider 27.5 wheels with 2.5-2.6 tires.
CVA is unique in that the lower linkage hangs below the bottom bracket. This allows the company to design bikes with shorter chainstays and it also allows for greater tuning of the overall suspension kinematic.
How does it work?
In a nutshell, the CVA system controls unwanted suspension movement with calibrated anti-squat provided by chain force, rather than relying on rear shock compression damping or manual lockouts. At the same time, CVA keeps the suspension active while climbing and descending, thanks to careful pivot placement which effectively tunes the amount of bump input required to overcome the anti-squat.
CVA is named for the path of the rear axle as the suspension cycles through travel. As the suspension is compressed, the rear axle moves past the sag point in a gradual, constantly varying arc, upward and inward toward the bike.
Niner’s CVA axle path is important. Thanks to this unique rear axle path, Niner suspension bikes benefit from carefully controlled chain growth in the first 30% of suspension travel which imparts an optimal degree of “anti-squat” force under pedaling loads.
Supple yet stable going uphill
The CVA axle path (and hence chain growth) maximizes anti-squat right at the sag point, or within the first 25-30% of suspension travel. Therefore, chain tension from pedaling force helps to hold the bike up in its travel, right at the sag point, and prevents it from squatting or bobbing under pedaling load.
Furthermore, CVA’s anti-squat is amplified in larger cogs, the gears used when a rider is pedaling uphill. This further minimizes pedal bob and loss of efficiency, particularly when climbing.
Yet the anti-squat stability is “overruled” by bump input, even going uphill. When bump inputs from terrain cause the CVA suspension to move past the sag point into travel, chain growth and anti-squat diminish. This prevents pedal kick-back and keeps the suspension supple and active. The rear wheel stays smoothly in contact with the ground and the rider maintains traction while pedaling.
Sensitive and supportive on descents
Beyond the sag point, chain growth and anti-squat are reduced to near zero. The drivetrain is effectively decoupled from the suspension as CVA moves deeper through travel, allowing the suspension full freedom to absorb impacts and track terrain. This keeps the suspension sensitive and fully active while descending.
Niner also tunes the suspension leverage ratio throughout the suspension travel. With a relatively higher leverage ratio early in the suspension stroke, the CVA design transfers more force from the rear wheel to the shock in the early stroke. This keeps the system hypersensitive to small bumps, allowing the rear wheel to stay smoothly in contact with the ground.
Deeper in travel, the leverage ratio is slightly reduced. Less force from the rear wheel is transferred to the shock shaft. This adds supportiveness to the mid-stroke and allows the shock to fully support the rider’s weight. A rider can pump and push against terrain without the bike moving too far into travel.
In the end stroke, the leverage ratio curve ramps up just enough to transfer more force to the shock. This overcomes the natural ramp-up of the air shock, giving a bottomless feel under big hits and hard landings.
Consistent and controlled overall kinematic
As CVA cycles through travel, a virtual or “instant center” of rotation around which the rear axle rotates migrates fore and aft, but always remains far in front of the bottom bracket. Keeping the instant center out front of the BB, rather than at or in line with it, helps keep the suspension behavior consistent across a range of different gearing choices, especially early in the suspension travel.
By adjusting linkage pivot locations, Niner can adjust the kinematic to achieve desired behavior in each phase of the suspension travel. Each bike family gets an overall kinematic to suit the purpose of the bike. And the CVA system does not rely heavily on shock tune to control unwanted movement. CVA shocks are tuned for consistency and control on the downhills.
Unlike other designs, the CVA lower link lies below the BB, allowing for short chainstays and agile trail manners. And in contrast to VPP or DW Link systems, the longer CVA links offer easier control over the leverage ratio.
Another CVA benefit: the relatively low average leverage ratio reduces the amount of shock air pressure needed to support rider weight and we use a longer shock. There’s more oil in longer shocks, which translates to consistent, smooth, effective damping and better reliability.
Belief of suspension
Ultimately, the goal of a suspension design is simple: to keep the rear wheel in contact with the ground, moving as freely as possible in all situations, yet controlling and minimizing unwanted, inefficient movement.
For more than a decade, Niner’s CVA has proven to do this particularly well. To learn more about CVA and the Niner mountain bikes, visit Niner’s website: https://ninerbikes.com/