There is tons of info on FOX’s website, and here’s some more on the EVOL shocks on Cat’s new RR.
The infinitely adjustable pressure setting in the extra volume (EVOL) air chamber regulates spring rate in the final portion of the stroke and controls the shock’s bottom-out characteristics.
Increasing air pressure in the EVOL air chamber gives a more progressive spring curve to protect against harsh bottom-outs.
Dropping air pressure provides a more linear curve to maximize usable travel. When combined with the infinite adjustability of the main air spring, the EVOL air chamber allows the shock’s spring curve to be tuned for any rider weight and/or terrain condition. Pressure in the EVOL air chamber is adjusted to control the shock’s bottom-out characteristics. Adjusting this pressure is similar to adjusting the main spring on a coil over shock.
As the main air chamber pressure is held constant, changes in the EVOL air chamber alter the final portion of the spring curve. The main chamber and the EVOL air chamber are connected by a port. As the shock is compressed, the main air chamber pressure will increase due to a decrease in volume. Eventually, the pressure in the main air chamber will match the pressure in the EVOL air chamber, at which point the EVOL piston will begin to move.
There also are high and low speed compression adjustments. The Low Speed Compression (LSC) adjuster affects compression damping during slow suspension movements such as G-outs or smooth jump landings. It also affects wheel traction and the harshness/plushness of the vehicle (note that low-speed has nothing to do with vehicle speed). Choose an LSC setting that gives good body control without causing excessive harshness or loss of traction.
The High Speed Compression (HSC) adjuster mainly affects compression damping during medium to fast suspension movements such as steep jump faces, harsh flat landings and aggressive whoops. The goal is to run as little high-speed compression damping as possible without bottoming.
Rebound also can be controlled. Rebound damping controls the rate at which the shock returns after it has been compressed. The proper rebound setting is a personal preference, and changes with rider weight, riding style and conditions. A rule of thumb is that rebound should be as fast as possible without kicking back or feeling bouncy.
For slower rebound, turn the rebound adjuster knob clockwise. For faster rebound, turn the rebound adjuster knob counter-clockwise.
By Mark Boncher