The Fox 40 Factory fork is a top-tier component engineered for high-performance downhill and freeride mountain biking. Known for its unmatched stiffness, adjustability, and plush travel, the 40 Factory is designed for riders who demand the highest level of control on the most technical descents. This guide will walk you through its installation, setup, maintenance, common troubleshooting, performance optimization, compatibility considerations, and comparison with similar models.

Tools Required

• Torque wrench [paid link] with appropriate hex bits
• Suspension pump (high-pressure)
• Allen key set
• Cable cutters (for brake routing)
• Calipers (for axle measurement)
• Suspension oil and seal kit (for service)
• Shock pump

Installing the Fox 40 Factory

Installation of the 40 Factory must be precise to ensure safety and optimal performance. Begin by verifying steerer tube compatibility with your head tube (typically 1.5” straight or tapered with reducers).

First, cut the steerer tube to the correct length. Install the crown race and press the fork into the head tube using a headset press. Secure the stem and top cap, ensuring all bolts are torqued to Fox’s recommended specifications.

Next, install the front wheel using the 20mm thru-axle system. Slide the axle through the lower legs and hub, then tighten the pinch bolts in a cross pattern to ensure even clamping. Lastly, route the brake hose properly through the fork guards using the provided clamps, and check that the hose length allows full range of motion without tension.

Adjusting the 40 Factory for Optimal Performance

Setting up the fork correctly is crucial for ride quality. Begin with setting the air pressure according to Fox’s rider weight chart. Use a shock pump to adjust the air spring through the top cap valve on the left leg.

Next, adjust compression and rebound damping. The 40 Factory features high-speed and low-speed compression, both accessible from the top of the right leg. Start with factory baseline settings and make minor adjustments during ride tests. The red dial at the bottom of the right leg controls rebound—set this based on terrain and rider feedback to maintain traction without harshness.

Sag setup is also important. With full gear, measure sag to fall between 15-20% of total travel. Adjust air pressure accordingly if outside this range.

Maintaining Your Fox 40 Factory

Routine maintenance ensures long-term reliability. Wipe down the stanchions after each ride and check for dirt or oil buildup. Inspect dust wipers regularly and replace them if there’s excessive contamination or leakage.

Service intervals include:

• Every 30 hours: Clean and lube the seals, inspect oil levels.
• Every 100 hours: Perform a full lower leg service with oil replacement and foam ring inspection.
• Annually: Complete damper service or send to an authorized Fox service center.

Neglecting service can lead to performance degradation and costly internal wear.

Troubleshooting Common Issues

Several common problems can arise with improper setup or extended use.

Harsh compression or bottoming out: Likely due to incorrect air pressure or compression settings. Check sag and damping adjustment.

Loss of travel or inconsistent feel: This may indicate air transfer between chambers or contamination inside the damper. A full service may be required.

Brake rubbing or noise: Check axle torque and that the fork lowers are evenly aligned. Resetting the caliper position can also help.

Oil weep at seals: Often a sign of worn dust wipers or over-lubrication. Replace seals and check oil levels.

Customizing for Your Riding Style

The 40 Factory offers wide customization. Riders can install volume spacers to alter the air spring curve. More spacers provide a progressive feel for aggressive descents, while fewer spacers allow a linear stroke.

Compression tuning allows you to fine-tune the feel for different terrain. For example, increase high-speed compression for big hits or fast bike park laps, and lower low-speed compression for more traction in technical rock gardens.

Additionally, the fork’s chassis accepts a variety of fender and brake configurations. Riders using 203mm or 220mm rotors can adjust the caliper adapter accordingly.

Optimizing the 40 Factory for Peak Performance

To fully extract the fork’s potential, pair it with a balanced rear shock such as the Fox DHX2 or Float X2. Suspension balance is crucial for maintaining geometry and traction.

Regular telemetry-based tuning—available at advanced bike shops—can also help dial in compression and rebound curves for your specific terrain and riding style. For racers, this level of optimization can significantly improve lap consistency and rider confidence.

Compatibility with Drivetrain and Wheel Standards

The Fox 40 Factory is compatible with:

• 20mm x 110mm Boost hubs (ensure correct spacing)
• 27.5″ or 29″ wheels, depending on the model
• Post-mount brake calipers for up to 220mm rotors

While drivetrain compatibility is largely independent of the fork, ensure that brake calipers align properly with rotor size and spacing. The fork also pairs best with bikes using DH geometry—typically 63-64° head angle and 200mm rear travel.

Comparing the Fox 40 Factory to Similar Models

When compared to the RockShox BoXXer Ultimate, the Fox 40 Factory stands out for its superior chassis stiffness and more adjustable damping circuit. While the BoXXer is lighter and more affordable, the 40 Factory offers a more planted feel in rough terrain and steeper lines.

Against the Öhlins DH38, the 40 Factory has broader OEM and aftermarket support. Öhlins offers plushness, but Fox’s damper is more tunable out of the box. The 40 also integrates better with common service tools and procedures.

For budget-conscious riders, the Fox 40 Performance Elite offers a similar chassis with fewer adjustments, but those who demand full customization will find the Factory version well worth the investment.

Final Verdict: Is the Fox 40 Factory Worth It?

The Fox 40 Factory is not just a fork; it’s a racing instrument. For riders who regularly tackle downhill courses, bike parks, or aggressive enduro stages, it delivers unmatched control, tunability, and durability. While the price tag is steep, its performance and longevity justify the cost—especially when serviced properly and customized for individual rider preferences. If downhill speed and precision matter most to you, the 40 Factory is absolutely worth the upgrade.