The Fox 40 Factory suspension fork is a benchmark component in the realm of downhill and gravity mountain biking. Known for its stiffness, tunability, and unmatched damping control, it has become a staple on professional DH race bikes. This guide offers a detailed overview of installation, tuning, troubleshooting, and maintenance for the Fox 40 Factory. We’ll also compare it with similar high-performance forks and examine its compatibility within different bike builds.

Tools Required

• 5mm and 6mm Allen keys [paid link]
• Torque wrench [paid link]
• Crown race setting tool
• Fork pump (compatible with high-pressure chambers)
• Suspension oil and measuring syringe
• Fox 20cc Float fluid
• Clean workspace and nitrile gloves

Installation of the Fox 40 Factory Fork

Installing the Fox 40 Factory fork demands attention to structural integrity and fitment precision. Begin by verifying steerer tube length and compatibility with your frame. Once the crown race is seated correctly using a crown race tool, insert the fork into the head tube. Ensure headset bearings are properly lubricated before compressing the system with the top cap and preload bolt.

For the axle, align the fork lowers precisely with the front hub’s axle path. Tighten the pinch bolts gradually and in sequence to avoid torsional imbalance. Fox recommends torquing the axle to 19 Nm and pinch bolts to 7 Nm.

Initial Setup and Adjustment

The 40 Factory fork is equipped with Fox’s GRIP2 damper, offering high- and low-speed compression and rebound adjustments. Riders should start with baseline settings from Fox’s tuning guide based on rider weight.

Set the air spring pressure using a fork pump. Riders typically start at 70-90 psi and fine-tune based on ride feedback. Use the red and blue dials to independently control compression and rebound. Adding tokens can increase progressiveness if bottom-outs occur too frequently.

Routine Maintenance Schedule

Fox recommends the following maintenance intervals for optimal performance:

• Every 30 hours: Clean and inspect seals, add Float Fluid through the bleed ports.
• Every 100 hours: Full lower leg service with oil change and foam ring inspection.
• Every 200 hours: Damper service, including seal replacement and oil refresh.

Using Fox’s suspension oil is critical to ensure damping consistency and lubrication compatibility. Always avoid using alternative lubricants, as they may degrade internal seals.

Troubleshooting Common Issues

Many performance issues with the 40 Factory arise from incorrect setup or lack of maintenance. For example:

• Harsh compression: Often caused by excessive air pressure or overly closed HSC settings.
• Frequent bottom-outs: May require additional air pressure or installation of volume spacers.
• Oil leakage at seals: Indicates worn wipers or contaminated oil, necessitating a lower leg service.
• Clicking or knocking sounds: Typically from dry bushings or loose crown bolts; check torque values and re-lubricate.

Always inspect for stanchion scratches or crown creaks during troubleshooting. These can indicate more severe issues that require professional service.

Customization and Performance Optimization

The Fox 40 Factory allows a high degree of customization to match terrain and riding style. Riders can change fork offset using aftermarket crowns or experiment with different damper tunes. Coil spring conversion kits are available for those seeking a more linear feel compared to the air spring’s progressive behavior.

Installing a fender via the pre-threaded mounts helps protect seals from trail debris. Additionally, upgrading to titanium hardware can reduce unsprung weight and slightly improve small bump compliance.

Comparing the Fox 40 Factory with Similar Models

When placed against models like the RockShox Boxxer Ultimate or the Öhlins DH38, the Fox 40 Factory holds its ground in tuning depth and small-bump sensitivity. The GRIP2 damper is more complex than RockShox’s Charger 3, but offers better damping adjustability. In terms of chassis stiffness, the 40 Factory slightly edges out its competition, offering superior tracking through high-speed chatter.

However, it is heavier than the Boxxer and less forgiving on setup errors. Riders seeking plug-and-play simplicity might prefer a simpler damper configuration, but those wanting maximum tuning potential will favor the Fox 40.

Compatibility with Other Components

The Fox 40 Factory fork is compatible with both 27.5″ and 29″ wheel sizes, depending on the specific chassis purchased. It uses a standard 20×110 Boost axle and fits rotors up to 223mm. The fork’s crown and steerer tube interface with both integrated and external headsets, provided the diameter matches the tapered steerer tube.

For cockpit integration, riders must use a direct-mount stem. Fox’s standard bolt pattern allows easy pairing with most DH stems, but torque settings must be adhered to avoid clamping damage.

It is also compatible with most modern headsets and frame geometries designed for dual-crown forks. However, frame manufacturers’ clearance guides should always be reviewed prior to installation.

Conclusion

The Fox 40 Factory is an elite-level suspension fork built for aggressive riding and precise performance. While it demands more maintenance and setup knowledge than some alternatives, it rewards the rider with customizable control and high-speed stability. When properly tuned and maintained, it delivers consistent performance over rugged terrain, making it a top choice for racers and dedicated gravity riders alike.