The Fox 40 Factory Suspension Fork is engineered for elite downhill and freeride mountain biking, offering class-leading damping control, stiffness, and adjustability. With its cutting-edge GRIP2 damper, lower leg bleeders, and EVOL air spring, the fork enhances ride comfort and precision over aggressive terrain. To fully capitalize on its performance potential, proper installation, setup, and maintenance are crucial. This guide details everything you need to know to maximize comfort with the Fox 40 Factory Suspension Fork.

Tools Required

• 6mm and 5mm Allen wrenches [paid link]
• Torque wrench [paid link]
• Crown race setter
• Star nut setter (if using a non-integrated headset)
• Suspension pump
• Suspension oil and seals (for service)
• Ruler or digital caliper [paid link]
• Clean rags and isopropyl alcohol
• Fox damper bleed kit [paid link] (for advanced maintenance)

Installation Guide for the Fox 40 Factory

Installing the Fox 40 Factory requires attention to both the steerer tube and dual-crown alignment. First, ensure the fork’s steerer tube is compatible with your frame’s headtube diameter and headset standard. The Fox 40 uses a 1.125–1.5” tapered steerer.

Start by cutting the steerer tube to the correct length. Use a guide to ensure a square cut. Fit the crown race securely using a crown race setter and slide the fork into the headtube. Align both crowns, ensuring the upper crown clamp bolts are torqued evenly. Install the front wheel and brake caliper before torquing the lower crown bolts.

Double-check axle torque and brake alignment. The axle should be flush with the lowers and tightened to Fox’s specified torque to maintain fork leg alignment. After mounting, inspect clearance between fork arch and the tire to prevent bottom-out interference.

Adjusting the GRIP2 Damper and EVOL Air Spring

The GRIP2 damper is a standout feature on the 40 Factory. It includes independent high- and low-speed compression and rebound adjustments. To enhance comfort, begin by adjusting the air spring:

• Inflate the EVOL air spring to match your rider weight. Fox provides recommended settings in psi for rider weight categories.
• Use a ruler to measure sag. Aim for 20–25% sag for optimal downhill comfort.
• Adjust volume spacers inside the air chamber to change the progressiveness of the spring curve.

For damping, set low-speed compression to moderate to prevent diving under braking while maintaining plushness. Dial in high-speed compression to resist harsh bottom-outs on big hits. Rebound should be quick enough to recover between hits but slow enough to avoid pogoing.

Routine Maintenance Practices

To maintain the plush feel of the 40 Factory fork, follow a routine maintenance schedule:

• Clean fork stanchions and seals after every ride using a lint-free cloth and isopropyl alcohol.
• Every 30 hours: Perform a lower leg service. Replace the bath oil, clean foam rings, and inspect the dust wipers.
• Every 100 hours: Complete a damper service. Bleed the GRIP2 damper using the Fox bleed kit [paid link] to remove air and refresh oil.
• Inspect the air spring assembly for leaks or wear during every 100-hour service.

Keep seals lubricated with Fox’s specified 20wt Gold oil, and never use general-purpose grease or unapproved lubricants.

Troubleshooting Common Setup Issues

Harsh initial stroke: This may indicate overinflated air pressure or dry seals. Check sag and consider adding a drop of suspension fluid to the dust wipers.

Inconsistent rebound feel: Often caused by air trapped in the damper or contaminated oil. A full damper bleed is required.

Fork not reaching full travel: Could be due to excessive volume spacers or under-inflation. Remove a token and re-check sag and air pressure.

Brake shudder or noise: Ensure crown bolts are evenly torqued and the headset is preloaded correctly. Misalignment in the crowns can amplify braking forces.

Customizing and Optimizing for Specific Terrain

The 40 Factory can be tuned for terrain-specific performance. For steep, rough descents:

• Add one volume spacer for a more progressive feel.
• Slightly reduce air pressure for better traction.
• Increase low-speed rebound damping for better control in successive hits.

For flow trails or bike parks:

• Run slightly less sag (~18%) for a more supportive mid-stroke.
• Decrease compression damping to increase responsiveness in rollers and berms.

Custom tuning of the GRIP2 damper via shim stack modification is possible, though best left to experienced suspension technicians.

Compatibility Considerations

The Fox 40 Factory is a dual-crown fork designed for downhill bikes with 20x110mm Boost hubs. It is not compatible with standard trail or enduro bike frames due to its axle-to-crown height and crown width.

Brake compatibility includes 203mm and larger rotors with post-mount calipers. Ensure your frame accommodates the fork’s larger turning radius and crown clearance. Use of a direct-mount stem designed for the 40’s top crown is required.

Comparison with Similar Suspension Forks

Compared to the RockShox Boxxer Ultimate, the Fox 40 Factory offers slightly more adjustability with its independent GRIP2 damping circuits. The Boxxer is lighter and easier to maintain but lacks the fine-tuning control of the 40.

The Öhlins DH38 provides excellent small-bump compliance, rivaling the 40’s plushness, but it lacks the wide service network and aftermarket support that Fox offers. Riders looking for the highest adjustability and serviceability will find the 40 Factory superior.

FAQs

What is the recommended air pressure for the Fox 40 Factory?
Refer to Fox’s rider weight chart, but as a general guide, a 180 lb rider should start at 80–85 psi.

How often should I service the 40 Factory fork?
Lower leg service every 30 hours, damper and air spring service every 100 hours.

Can I use a 29” wheel with the Fox 40 Factory?
Yes, if you have the 29” model. Ensure tire clearance is adequate when fully bottomed out.

Why does my fork feel sticky at the beginning of travel?
This is often due to dry or dirty seals. Clean and lubricate the stanchions, and perform a lower leg service if needed.

Is the 40 Factory fork good for enduro riding?
No. It is specifically designed for downhill use due to its dual-crown design and weight.

Can I reduce travel on the 40 Factory?
Travel adjustments are possible by changing internal spacers, but this requires complete disassembly and is not recommended for casual users.