Position Sensitive Anti-Squat by Dave Weagle

As bicycle suspension systems become more and more refined, designers strive to reduce weight, increase lateral stiffness, travel, and traction, and at the same time improve efficiency. As suspension travel increases, improvements in traction and comfort are realized, but maintaining an efficient ride becomes a greater challenge. The extra comfort and traction afforded by suspension is usually accompanied by a noticeable compromise in the efficiency of the bicycle in general. That is, you don't go as fast or as far for a given amount of effort. There have been numerous attempts to devise a system that would give good performance over the bumps and not waste any precious energy due to unwanted suspension movement. The patented dw-link is the most effective solution thus far in achieving that goal. To understand the theory behind the dw-link let's start with mass transfer. Mass transfer is a part of any movement; in particular we are concerned with the transfer that happens when you accelerate a bicycle.

A bicycle has the highest ratio of center of mass height to wheelbase of any vehicle (other than a unicycle). In the accompanying illustration, (1) represents the center of mass. Mass transfer happens on any type of bicycle, from road bikes to full downhill rigs. Every time you accelerate, your mass transfers rearward on the bike (2). When you ride a wheelie, all of your mass transfers to your rear wheel. When you do an endo, all of your mass transfers to the front wheel. Anyone who has ridden a bicycle can probably relate to this!

Unchecked, your rear suspension will react to this mass transfer by compressing and rebounding with each acceleration. The suspension's purpose is to absorb bumps, reduce vibration, and maintain grip through vertical compliance, and will compress due to acceleration unless stopped by shock damping or a counter-force from the suspension.

If there was no damper attached to your suspension (in other words if it were merely a spring), every suspension compression would be followed by an immediate and forceful rebounding force. All of the energy put into the spring would be released back into the suspension like a pogo stick. This would result in the system vibrating uncontrollably and would be more of a detriment to traction and comfort than an aid. To control this situation, a suspension system uses a damper to subdue spring oscillations and rebound forces. Many suspension systems sold today rely on an additional type of damping to in order to control their reaction to mass transfer. The use of heavy compression damping of the suspension at low shaft speeds has become a common feature on bicycle suspensions. So what's wrong with using damping to reduce the unwanted suspension movement?

A damper controls spring oscillations and rebound forces by converting mechanical energy to heat and dissipating it. The damper (your rear shock) and its ability to convert mechanical energy into heat is a double-edged sword. With heavy compression damping, when you accelerate a vehicle and the suspension compresses, a significant percentage of that energy is converted to heat and dissipated rather than used to drive the wheel. If the effects of mass transfer can be countered without excessive shock damping (4), then you can use the saved energy to move the bike forward, resulting in a more efficient suspension!

dw-link counters the effects of mass transfer with the world?s first suspension using a patented position sensitive anti-squat response.

You might be asking yourself, "What exactly is 'position sensitive anti-squat''? Anti squat is a force that balances the effects of mass transfer on the suspension, giving the best possible bump compliance, while at the same time providing excellent energy efficiency. There are two forces that combine to create anti-squat; chain pull and driving force. Chain pull force is multiplied through your rear cogs and wheel as a lever creating driving force. Because of this leverage, driving force is always the greater than chain pull force.

Mass transfer and driving force are not accounted for in most suspension designs and analysis to date, thus missing the primary cause of and respective solution to unwanted suspension movement. That is, designers have worked on solving the lost energy problem by neutralizing the effects on the suspension from chain tension but have missed or ignored mass transfer and driving force, leaving the true movement (squat) from acceleration unsolved.

The dw-link patents and suspension designs are based on solutions that have resulted from this important observation. The dw-link creates a balancing force to eliminate the squat caused by mass transfer. This force is carefully tuned for near 100% anti-squat in the first and second portions of the travel with a lessening anti-squat response deeper in the travel to reduce pedal feedback (3) to imperceptible levels. This allows the suspension to feel very efficient with minimal shock damping while also exhibiting excellent performance in traction and braking with low pedal feedback.

Check out the animation of the dw-link equipped Mojo in action.

Summary:
dw-link is the world's first suspension system that takes into account mass transfer and uses a position sensitive anti-squat response to balance it. The end result is that the suspension can use much less compression damping than other systems, increasing traction and conserving energy at the same time. Real world experience bears this out with the dw-link designs consistently getting rave reviews from riders and magazines.