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DHX Air 4.0

Installing Your Shock  |  General Maintenance  |  Before You Ride  |  Measuring Sag  |  Setting Sag  |  Adjusting Rebound  |  ProPedal: Dial or Switch  |  Boost Valve  |  Service Intervals  |  Important Safety Information  |  Stuck Down Shock  |  Air Sleeve Maintenance  |  DHX Air Explained


0.93 lbs./422 g
(8.5" x 2.5" No reducers)


position-sensitive Boost valve, adjustable ProPedal 2-position dial or switch, adjustable tuning range via Schrader valve, adjustable air spring pressure, rebound adjust



intended use

downhill, freeride, all-mountain, cross-country

Installing Your Shock

If you are installing your shock on a bike in which the shock is not original equipment:

  1. Install the shock.
  2. Remove the main air chamber air cap and let all the air out of the main air chamber.
  3. Carefully cycle the suspension through its entire travel.
  4. Check that all parts of the shock are clear of the frame and swingarm as it cycles through the travel.
  5. Pressurize your main air chamber to a minimum of 50 psi and no more than 300 psi. You will tune to a more specific air pressure in the Setting Sag section below.
  6. Set sag.

General Maintenance

There may be a small amount of air sleeve lubricant residue on the body. This is normal. If this residual air sleeve lubricant is not present, this is an indication that the air sleeve should be re-lubricated. Some other things to consider for all shock models:

Before You Ride

  1. Clean the outside of your shock with soap and water and wipe dry with a soft dry rag. Do not use a high pressure washer on your shock.
  2. Inspect entire exterior of shock for damage. The shock should not be used if any of the exterior parts appear to be damaged. Please contact your local dealer or FOX Racing Shox for further inspection and repair.
  3. Check that quick-release levers (or thru-axle pinch bolts) are properly adjusted and tightened.
  4. Check headset adjustment. If loose, adjust according to manufacturer’s recommendations.
  5. Check that brake cables or hoses are properly fastened.
  6. Check that the front and rear brakes operate properly on flat land.

Setting Sag

You can also view a Flash video on Setting Sag.

To set sag on your DHX Air 4.0:

  1. Measure sag, and compare it to the recommended sag setting shown in the Air Spring Settings table below. Continue if the sag is not to specification.
  2. Locate the Schrader air valve on the shock and remove the air valve cap.
  3. Screw the FOX Racing Shox High Pressure Pump onto the air valve until the pump shows pressure on the gauge. Do not over-tighten.
  4. Add air pressure until desired pressure is shown on the gauge. Refer to the Air Spring Settings table below for the proper sag setting.
  5. Unthread the pump from the air valve and measure sag.
  6. Repeat steps 2-5 until proper sag is achieved, then replace the air valve cap.


Shock Travel

Recommended Sag









Adjusting Rebound

Rebound controls the rate at which your 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 and pushing the rider off the saddle.

The rebound dial has approximately 22 clicks of adjustment.

For slower rebound, turn the red adjuster knob clockwise.

For faster rebound, turn the red adjuster knob counterclockwise.


Adjusting the ProPedal Dial

The ProPedal adjustment knob allows the rider to adjust the amount of ProPedal damping. ProPedal damping affects the initial part of the compression stroke and is designed to control pedal-induced suspension bob. Since suspension designs vary, not all bicycles require the same degree of ProPedal damping.

There are 15 clicks of adjustment.

For lighter ProPedal damping, rotate the ProPedal knob (shown below) counterclockwise.

For increased ProPedal damping, rotate the ProPedal knob clockwise.


Adjusting the ProPedal Switch

The ProPedal adjustment switch allows the rider to adjust the amount of ProPedal damping using a 2-position switch, which varies from FIRM to SOFT. ProPedal damping affects the initial part of the compression stroke and is designed to control pedal-induced suspension bob.

The switch has two (2) positions:

For more ProPedal damping, rotate the ProPedal switch clockwise.

For lighter ProPedal damping, rotate the ProPedal switch (shown below) counterclockwise.

Boost Valve

The Boost Valve creates a position-sensitive damping scheme that allows for a seamless transition from efficient ProPedal to square-edge bump absorption to a bottomless end-of-stroke feel. The Boost Valve also decouples the ProPedal and the factory-set bottom-out resistance, enabling ProPedal adjustments to be made without affecting the compression damping curve.

The Boost Valve is not adjusted directly. Instead, its behavior and performance characteristics are influenced by the air pressure setting in the reservoir and by adjusting the ProPedal knob.

To change the compression damping characteristics of your DHX Air 4.0 shock, attach a FOX High Pressure Pump to the air valve on the reservoir:

For a firmer ride, add 10 - 15 pounds of air pressure (to a maximum of 200 PSI).

For a softer ride, decrease the shock's air pressure 10 - 15 pounds by using the pump's bleed valve (to a minimum of 120 PSI).

Ride your bike and verify the settings before repeating the procedure.

Never ride your bike with more than 200 PSI or less than 125 PSI in the reservoir air chamber.
Doing so can damage your shock and require repairs that are NOT covered under warranty.

ProPedal + Boost Valve Interaction

Certain aspects of the Boost Valve can influence the ProPedal adjustment.

If the ProPedal adjustment knob is fully counterclockwise (lightest ProPedal damping position) and the compression damping is still too strong, attach a shock pump to the Schrader valve on the reservoir and reduce the pressure 10 - 15 psi. Repeat to achieve the desired compression damping.

If there is not enough compression damping with the ProPedal knob fully clockwise, add 10 - 15 psi to the Boost Valve until desired compression damping is achieved.




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