Without proper adjustment, your rear shock can have you either bottoming out or bouncing off your bike like it has an ejector seat. The Fox DHX 4.0 is a high-end coil shock that keeps your ride as stiff or plush as you want it to be. Whether you're riding a Specialized BigHit or any other mountain bike, the adjustment instructions for this shock are essentially the same. Adjustments can be dialled-in with a few test rides and minimal effort.
Measure (in millimetres) the distance between the centres of the shock mounting bolts, located at both ends of the shock. Write the measurement on a piece of paper.
Put on your helmet and any riding gear you normally wear. Sit steady on the bike while balancing yourself with your hand on a wall. Distribute your weight between the seat, pedals and handlebars, as you would while riding. Have an assistant measure and note the length between the centres of the shock mounting bolts.
Subtract measurement #2 from measurement #1. This figure is current sag.
Consult the "Coil Spring Setting Guidelines" table on the Fox Racing Shox website. If sag is outside of recommended settings in the table, continue to Step 5. Otherwise, continue to "Adjust Rebound" section. As a general rule of thumb, sag should be 30 to 40 per cent of the shock's total travel on a downhill or freeride bike, although it can be slightly higher or lower depending on personal preference.
Find the large dial at the top of the coil spring, this is the preload ring. Turn the preload ring counterclockwise to stiffen the shock if sag is lower than recommended on the table. Turn the preload ring clockwise to loosen the shock if sag is higher than recommended on the table.
Continue taking measurements and adjusting the preload ring until the recommended sag is achieved.
Determine your personal preference for rebound. Rebound is the speed your shock decompresses after being compressed. This setting is a matter of personal preference but a general rule is for the shock to rebound as fast as possible but not so fast that it springs you off the seat. The Rebound Dial is the red knob on your shock.
Turn the dial clockwise for slower rebound. Turn counterclockwise for faster rebound.
Take a ride on your preferred terrain and make adjustments to the Rebound Dial as needed.
Determine your personal preference for ProPedal damping. The ProPedal adjustment dial controls the amount of pedal bob (i.e. the amount of movement in your shock that occurs while pedalling). The ProPedal Dial is the blue knob on your shock.
Turn the dial counterclockwise for lighter ProPedal damping. Turn the dial clockwise for greater ProPedal damping.
Take a ride on your preferred terrain and make ProPedal Dial adjustments as needed.
Adjust the compression dampening characteristics of your shock by adding or removing air from the reservoir. Attach a high-pressure shock pump to the Schrader valve on the reservoir and check psi.
Add air pressure for a firmer ride. Do not exceed 200 psi of air pressure.
Decrease air pressure for a softer ride by using the pump's bleed valve. Do not decrease below 125 psi of air pressure.
Take a ride on your preferred terrain and make air pressure adjustments as needed.
Extend the life of your shock by keeping it clean and well adjusted. If your shock is underperforming or is visibly damaged, it may require a rebuild. Unless you are an experienced bike mechanic, have the rebuild done by a professional bike service centre.
This article concerns the Fox DHX 4.0, not the Fox AIR DHX 4.0.