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The Highs and Lows of Rebound

Rebound has a dramatic effect on how a mountain bike feels and performs. With today’s app update, ShockWiz offers Suggestions for Low and High Speed Rebound.

While riding, the suspension is constantly moving; compressing from bumps and rider inputs and then extending as the spring pushes back. Rebound damping controls the extension phase of these movements, influencing and sometimes dictating the dynamics of the bike.

Typically, the speed of suspension movement during a compression has a wide range due to the large forces that come from the trail and rider. On the other hand, speeds during rebound are normally slower and grouped closer together. During extension, the predominant forces come from the spring trying to push back to its natural position as quickly as it can, and the low speed rebound (LSR) damper trying to slow it down to return the suspension in a controlled manner.

The dynamics of the system get a little more complicated when you add in high speed rebound (HSR). While not always externally adjustable, many forks and shocks have HSR which is set at the factory, such as RockShox products with Rapid Recovery. HSR limits the rebound force applied at higher velocities (or ‘opens up’) so the suspension can recover. The theory behind this is that if LSR is set slow enough to create enough force at low speeds, it may create too high a force at high speeds and cause packing over consecutive bumps. A good combination of high and low speed rebound creates suspension that can both recover quickly from deep impacts while still providing control at lower speeds.

As discussed in the Goldilocks article, rebound damping is a balance between recovery and control, with good damping avoiding both the pogo and packing sensations. Reducing HSR can provide quick recoveries from impacts to help avoid packing but, lower it too far and it can reduce the ability of the LSR damper from controlling movements at intermediate speeds. In effect, HSR controls how much LSR force is available by limiting the maximum force.

In general terms, LSR has a much greater influence on the ride than HSR does. If you only have one rebound adjuster, do not fret. Tune LSR to give a good balance between control and recovery.

If you have an HSR adjuster, it needs to be set so that LSR can do its job while still allowing the suspension to recover quickly from multiple impacts. In this case, LSR and HSR should be tuned as a pair until ‘OK’ is indicated for both.

To help achieve the best results quickly, ride trails that have rough features such as rock gardens as well as jumps, drops or square edge bumps. These features give ShockWiz the suspension movements needed to analyse rebound performance.