The Fox 40 Factory is a premier choice among mountain bike suspension forks, especially for gravity-focused disciplines such as downhill and freeride. Renowned for its strength, adjustability, and race-proven performance, the 40 Factory is engineered for riders who demand precision and control on the most aggressive terrain. This article explores every technical detail a rider or mechanic should understand—from installation to optimization—to determine whether the Fox 40 Factory truly stands as the best in its class.
Tools Required:
- Torque wrench [paid link] with appropriate bits
- Allen key set (4mm, 5mm, 6mm)
- Suspension pump
- Shock oil and syringe (for service)
- Clean rag and isopropyl alcohol
- Crown race setter
- Stanchion clamp or fork stand
Installation of the Fox 40 Factory Fork
Installing the Fox 40 Factory requires precision and proper preparation, especially due to its dual-crown architecture. This fork is built for 20mm thru-axles and tapered steerers.
Begin by removing the old fork and cleaning the head tube thoroughly. Install the crown race onto the steerer tube using a race setter, ensuring it seats evenly. Slide the steerer through the head tube and fit the upper crown, aligning the fork legs before tightening the stem and upper crown bolts in a cross-pattern sequence. It’s critical to set the fork’s axle-to-crown height appropriately to maintain the bike’s geometry.
Install the front wheel with the 20mm axle and secure it by tightening the pinch bolts to spec. Confirm brake mount compatibility (Post Mount 203mm standard), and align the caliper for accurate rotor clearance.
Adjusting Suspension Settings
The Fox 40 Factory offers extensive external adjustability through high- and low-speed compression dials, rebound knobs, and air pressure via the EVOL air spring.
Begin by setting the rider sag to 15–20% of travel. Adjust air pressure accordingly using a suspension pump. Then fine-tune low-speed compression for support during pedaling and cornering, and high-speed compression to control bottom-out during big hits. Rebound damping should be set based on rider weight and terrain preference—slower for chunky rock gardens, faster for smoother trails.
The GRIP2 damper provides precise adjustability and is ideal for riders who demand tuning accuracy.
Routine Maintenance Guidelines
Regular maintenance ensures the Fox 40 Factory performs reliably over time. Basic service should occur every 30 riding hours, with a full damper and air spring service recommended every 125 hours.
For the lower leg service, remove the lowers using a 10mm socket and collect used oil. Clean internal parts, replace dust wipers if needed, and refill with fresh 20wt Gold oil. Always use a torque wrench [paid link] to reinstall bolts to factory spec.
During a full service, rebuild the damper using factory-recommended procedures and tools. Replace seals, inspect the stanchions for wear, and refresh the air spring assembly to prevent stiction.
Troubleshooting Common Set-Up Issues
Some riders experience harshness or lack of travel, often caused by incorrect air pressure or over-damping.
If the fork feels harsh at the beginning stroke, reduce low-speed compression or ensure the air spring is not over-inflated. If bottom-out occurs too easily, increase high-speed compression or consider volume spacers to ramp up the spring rate.
Fork creaking, especially near the crown, is usually due to improperly torqued crown bolts or contamination between the stanchions and crowns. Clean and reapply a thin layer of carbon assembly paste if needed, then re-torque to spec.
Customization and Optimization
Customization is a key strength of the 40 Factory. Riders can modify the fork using air volume spacers to adjust progression. Adding spacers will increase bottom-out resistance and improve mid-stroke support for aggressive riders.
Custom tuning of the GRIP2 damper can also be performed by suspension specialists, allowing changes to shim stacks for those who require ultra-specific damping curves.
Aftermarket options like Kashima-coated stanchions, custom decals, or titanium hardware can also be installed to reduce weight and personalize the fork’s aesthetic.
Compatibility with Drivetrain and Frame Standards
The Fox 40 Factory is compatible with most downhill frames using 1 1/8” straight or tapered head tubes, thanks to the adjustable steerer lengths and top crown configurations.
Brake mounting supports 203mm rotors as standard, with adaptors available for larger sizes. Wheel compatibility is limited to 27.5″ and 29″ depending on the model chosen. Axle spacing is 110mm Boost for modern downhill hubs.
It’s not intended for use with short-travel trail bikes or XC frames due to its weight and axle-to-crown height. Riders must ensure their frame and cockpit can accommodate the dual crown structure and steerer clearance.
Comparing the Fox 40 Factory to Similar Forks
When compared to the RockShox BoXXer Ultimate or Öhlins DH38, the Fox 40 Factory excels in small bump sensitivity and overall stiffness. Its EVOL air spring and GRIP2 damper offer more tuning range than the DebonAir and Charger 3 counterparts in many rider tests.
However, the BoXXer is lighter and may appeal to competitive racers focused on marginal gains. Öhlins provides a more supple ride feel but can lack the same adjustability without external tools.
The Fox 40 Factory strikes a strong balance of reliability, stiffness, and tuning flexibility, making it a top contender for both park riders and professional racers.
Final Verdict
The Fox 40 Factory remains a standout in the world of downhill mountain bike suspension. Its high-performance chassis, superior damping control, and customizable air spring make it an elite choice for those tackling aggressive trails. While not the lightest option, its reliability and tunability more than compensate, especially for riders who prioritize consistency and control under extreme conditions.
For riders seeking the best in adjustability, durability, and race-ready performance, the Fox 40 Factory is a strong candidate for the best suspension fork for mountain biking.