The Fox 40 Factory suspension fork has earned a reputation as one of the most elite, race-ready downhill forks on the market. With its precision damping, unmatched stiffness, and superior adjustability, it caters to aggressive riders demanding peak performance on challenging descents. This guide covers everything from installation to fine-tuning and maintenance, giving you the knowledge needed to get the most out of your Fox 40 Factory.

Tools Required

• Torque wrench [paid link]
• Allen key set (2mm to 8mm)
• Crown race setting tool
• Suspension pump
• Grease and thread locker (as specified)
• Caliper alignment tool
• Shock oil and suspension service kit (for advanced maintenance)
• Digital calipers (for measuring sag and travel)
• Isopropyl alcohol and clean cloth

Initial Setup and Installation

Installing the Fox 40 Factory fork correctly is crucial for long-term performance. Before beginning, confirm that your frame is compatible with a dual crown fork and has the proper headtube and axle spacing.

Begin by pressing the crown race onto the steerer tube using the appropriate tool. Slide the fork into the headtube, ensuring the upper and lower crowns are aligned correctly. Adjust the crowns to the manufacturer-recommended spacing and torque the pinch bolts evenly. It is essential to preload the headset properly without introducing play or excessive drag.

Once installed, secure the axle into the dropout using the pinch bolts and verify alignment. Incorrect axle positioning can lead to stiction and poor fork performance.

Damping Adjustment and Setup

The Fox 40 Factory comes equipped with high- and low-speed compression adjusters, as well as high- and low-speed rebound controls. This level of tuning allows for precise control over how the fork behaves under different trail conditions.

For compression:

• Set the low-speed compression to manage brake dive and cornering support.
• Use the high-speed compression to handle big hits and drops.

For rebound:

• Adjust low-speed rebound for traction and control over rolling terrain.
• Modify high-speed rebound to prevent harsh top-outs after jumps.

Air spring pressure should be set according to rider weight and riding style. Use a suspension pump to reach the desired PSI, checking sag with digital calipers. Aim for 20–25% sag for aggressive downhill riding.

Maintenance and Service Intervals

Routine maintenance ensures optimal performance and extends the fork’s lifespan. Clean the stanchions after every ride using a clean, lint-free cloth and inspect for oil residue, which may indicate seal wear.

Basic service:

• Lower leg service every 30 hours: clean and re-lube bushings, replace bath oil.
• Full damper and air spring service every 100–125 hours or annually.

Advanced service requires disassembly of the damper and air spring, using proper tools and following the service manual closely. Replace worn seals, inspect internal components for wear, and refill with the specified volume of Fox suspension oil.

Common Troubleshooting Issues

Excessive stiction or harshness is often due to dry or contaminated wiper seals. Perform a lower leg service and verify oil levels.

Fork diving too quickly indicates too little low-speed compression or insufficient air pressure. Increase air pressure or adjust the compression dial clockwise.

Inconsistent rebound might be the result of air in the damper. Bleed the damper if necessary, or perform a full damper service.

Clunking noises may come from loose crown bolts or headset bearings. Check torque specs and re-secure all fasteners.

Customization and Performance Tuning

The Fox 40 Factory can be finely tuned beyond its out-of-box performance. Volume spacers (also known as tokens) allow you to adjust the spring curve by increasing or decreasing end-stroke ramp-up. Adding spacers results in a firmer feel toward bottom-out, which is ideal for aggressive, high-impact riding.

Axle-to-crown height and offset can be modified using aftermarket crowns to suit different frame geometries or rider preferences. Custom decals and protective kits are available to personalize the fork while shielding the stanchions and lowers from debris.

Compatibility with Drivetrain and Frames

The Fox 40 Factory uses a 20x110mm Boost thru-axle, compatible with most modern downhill wheelsets. The steerer tube is tapered or straight 1 1/8″, depending on the model, and it requires a compatible headset.

Ensure your front brake is compatible with the 203mm post-mount standard. Larger rotors will require adaptors. Cable routing should be planned to avoid rubbing against the crown or stanchions, especially in tight cockpit setups.

Comparison with Similar Models

When compared to other downhill forks like the RockShox BoXXer Ultimate or the Öhlins DH38, the Fox 40 Factory stands out for its ultra-plush feel, Kashima-coated stanchions, and comprehensive tuning options. Riders often choose the Fox 40 for its ability to remain supple over small bumps while offering progressive bottom-out resistance.

The BoXXer is slightly lighter and more budget-friendly, making it attractive for competitive riders looking to save grams. The Öhlins fork appeals to those preferring coil-sprung performance with a more linear feel. However, the Fox 40 Factory strikes a balance between weight, adjustability, and durability that many top riders prefer.

FAQs

1. What is the recommended sag for the Fox 40 Factory?
20–25% of total travel is optimal for most downhill applications. Use a digital caliper [paid link] to measure sag accurately.

2. How often should I service my Fox 40 Factory fork?
Perform a lower leg service every 30 hours of riding and a full damper and air spring service every 100–125 hours.

3. Can I use the Fox 40 Factory for enduro riding?
The fork is designed specifically for downhill riding. Its weight and dual crown construction make it less suitable for enduro applications.

4. What is the air pressure range for this fork?
The air spring is tunable within a wide PSI range, typically between 60–120 PSI depending on rider weight and preference.

5. Can I install this fork on any mountain bike frame?
No. Your frame must be rated for a dual crown fork and have the proper headtube dimensions and fork clearance.

6. What makes the Kashima coating beneficial?
Kashima reduces friction, enhances durability, and provides a smoother, more responsive ride compared to non-coated stanchions.