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.
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™.
Continue to CBF™ Explained.