The Fox 40 Factory suspension fork is a top-tier downhill and freeride fork known for its stiffness, tunability, and superior damping control. To maximize its performance, precise setup and regular maintenance are essential. This guide offers expert instructions on how to adjust, maintain, and optimize your Fox 40 Factory for better performance. It also covers compatibility details and comparisons with similar high-end models to help riders make informed choices.
Tools Required
- 5mm and 6mm hex wrenches
- 26mm and 32mm sockets
- Torque wrench [paid link]
- Shock pump
- Fox 5wt Teflon-infused fork oil
- Clean rags and isopropyl alcohol
- Digital caliper [paid link] (optional)
- Suspension-specific grease
Installation of the Fox 40 Factory
Proper installation is the first step in achieving top performance from your Fox 40 Factory fork. Ensure the steerer tube is properly cut and the crown race is correctly seated. The lower crown bolts must be torqued to spec, usually around 5.1 Nm, to prevent creaking and misalignment.
The axle should be torqued evenly on both sides using the specified pattern. Start by snugging the pinch bolts, then torque the axle to 19.5 Nm. Re-check alignment before tightening the pinch bolts to 5.1 Nm. Ensure the fork is properly aligned within the headset to prevent handling issues.
Initial Setup and Sag Adjustment
Start by setting sag, which is essential for proper fork behavior. The Fox 40 Factory uses an air spring system in the right leg. Inflate the air spring to a pressure that achieves 15-20% sag when the rider is in full gear. This usually corresponds to 60–90 psi for most riders depending on weight and riding style.
To measure sag:
- Sit on the bike in riding position.
- Slide the rubber o-ring on the stanchion to the dust seal.
- Carefully dismount without compressing the fork further.
- Measure the distance the o-ring moved. This should equal 15–20% of the fork’s travel (typically 40-50 mm for the 203 mm travel).
Compression and Rebound Tuning
High-Speed Compression (HSC)
Located at the top of the right fork leg, this adjuster controls resistance to big impacts. Start at the middle setting and increase clicks clockwise to reduce bottom-out or open it counter-clockwise to improve suppleness over high-speed chatter.
Low-Speed Compression (LSC)
Also on the right leg, this adjuster affects fork movement during braking, cornering, and pumping. Tune it to balance support with traction. Use higher LSC settings for bike parks and technical terrain, and lighter settings for more responsive steering in loamy trails.
Rebound Damping
The red knob at the bottom of the right leg adjusts rebound speed. Start from fully closed and open 8–10 clicks. Fine-tune based on terrain—slower for smoother trails and faster for aggressive, rocky lines to maintain contact with the ground.
Air Spring Volume Spacers
The 40 Factory allows for fine-tuning progression by adding or removing volume spacers. Adding spacers increases bottom-out resistance, ideal for aggressive riders or big jumps. Fewer spacers yield a more linear feel, suitable for rough, high-speed terrain where maintaining traction is key.
To modify volume spacers:
- Deflate the air spring.
- Remove the top cap with a 26mm socket.
- Install or remove spacers from the top of the air shaft.
- Reassemble and torque to 18 Nm.
Routine Maintenance
Routine service is critical to performance. Lower leg service should be performed every 40 hours of ride time. This involves:
- Removing the lower legs.
- Cleaning and inspecting seals and bushings.
- Replacing bath oil with 30cc of Fox 5wt Teflon-infused oil per leg.
- Reinstalling with new crush washers and greasing the foam rings.
Annually, or every 100–125 hours, perform a full damper and air spring service. This ensures the FIT GRIP2 cartridge maintains consistent damping and that seals remain effective.
Troubleshooting Common Set-Up Issues
Harsh Initial Stroke: Reduce low-speed compression or slightly lower air pressure. Check for dry seals or insufficient lower leg lubrication.
Bottoming Out Frequently: Increase high-speed compression or add volume spacers. Also, verify correct air pressure is being used.
Fork Feels Dead or Slow: Rebound may be too slow; open it incrementally. Damper oil degradation may also be a factor—consider a full service if the issue persists.
Clicking Noise or Creaking: Inspect crown bolts and headset for proper torque. Creaks are often caused by under-torqued crown bolts or dry interfaces.
Customization for Better Performance
The Fox 40 Factory offers a high level of personalization. Riders can:
- Swap to titanium coil conversion kits for a linear feel and improved small bump compliance.
- Customize damping curves through GRIP2 tuning services for race-level optimization.
- Upgrade to Kashima-coated stanchions (if not already equipped) to reduce friction.
Brake mounts and axle-to-crown height can also be customized to match different frame geometries, allowing compatibility with varied downhill frames or mullet setups.
Compatibility with Drivetrain and Wheel Systems
The Fox 40 Factory is designed around 20mm x 110mm Boost DH front hubs. It is not cross-compatible with standard Boost 15mm hubs. Brake mount is post-style 203mm minimum, allowing for up to 220mm rotors with adapters.
It’s fully compatible with modern downhill stems and direct-mount configurations. Ensure the steerer length and diameter match your frame’s headset requirements before purchase.
Comparison with Similar Forks
When compared to the RockShox BoXXer Ultimate, the Fox 40 Factory offers more tunability through the GRIP2 damper. While the BoXXer uses a DebonAir spring and Charger 2.1 damper, many racers prefer the Fox’s high-speed adjustability and stiffer chassis.
Against the Öhlins DH38 m.1, the 40 Factory remains lighter and more commonly supported in aftermarket tuning communities. Riders seeking a balance of race-ready stiffness and field-serviceable parts often favor the Fox model.
Conclusion
The Fox 40 Factory is a highly adjustable and performance-oriented suspension fork tailored for demanding downhill riders. With the right adjustments and maintenance, it delivers precise handling, control, and reliability across varied terrain. Mastering its setup unlocks the full potential of your ride.