The Fox 40 Factory is a premium downhill suspension fork engineered for performance at the highest level of gravity racing. As part of Fox’s elite Factory Series, the 40 is distinguished by its Kashima-coated stanchions, advanced damping technology, and full adjustability. This article delves into the technical details, covering installation, setup, maintenance, compatibility, and performance tuning specific to the Fox 40 Factory.

Tools Required

• Torque wrench [paid link] with appropriate bits
• Allen wrenches [paid link] (4mm to 8mm)
• Crown race setting tool
• Suspension pump (for air models)
• Caliper or ruler (for axle to crown and sag setup)
• Fox 40-specific seal driver (for maintenance)
• Suspension oil and grease
• Isopropyl alcohol and clean rags

Installation Procedure

Proper installation of the Fox 40 Factory begins with an accurate steerer tube cut and precise headset fitting. The fork is dual-crown, necessitating exact alignment and torque of both upper and lower crowns.

Begin by installing the crown race onto the steerer tube using the race setting tool. Slide the steerer through the head tube, position the upper crown, and apply manufacturer-specified torque to the steerer tube pinch bolts. Attach the handlebars and stem, ensuring all bolts are evenly torqued. Lastly, install the front wheel and brake caliper, aligning the rotor carefully within the caliper body.

Due to the inverted axle design, ensure that the floating axle system is correctly tensioned using Fox’s pinch bolt and axle nut procedure. This alignment is crucial for consistent fork performance and stiction-free movement.

Adjustment and Setup

The 40 Factory allows for full suspension tunability via its GRIP2 damper and EVOL air spring (for air models), or coil setup in select variants. Riders must first determine the correct spring configuration based on their weight and riding terrain.

Air models require setting the sag by adjusting the air pressure using a suspension pump. Ideal sag ranges from 15-20% of total travel. Rebound and compression damping are controlled via dedicated high-speed and low-speed adjusters. Starting with baseline settings recommended in the Fox tuning guide ensures a balanced ride. Adjustments should be made incrementally, testing between runs for optimal performance.

Routine Maintenance and Service Intervals

To preserve factory-level performance, routine maintenance is essential. Lower leg service is recommended every 40 hours of riding, involving oil replacement, seal inspection, and cleaning of the stanchions and bushings.

Remove the lower legs by releasing the oil from the drain ports and removing the foot nuts. Inspect and clean all internal surfaces, replace wiper seals using a Fox-specific seal driver, and refill with the appropriate volume of suspension fluid. Reassemble carefully, ensuring no debris is trapped.

Full damper and air spring service should be conducted every 100–125 hours or annually. For this, Fox recommends servicing by certified technicians due to the complexity and need for specialized tools.

Troubleshooting Common Issues

Common setup issues include excessive stiction, harshness, or a lack of travel. These are often the result of improper air pressure, incorrect rebound settings, or internal contamination.

If the fork feels harsh off the top, reduce low-speed compression or increase air volume using spacers. If excessive brake dive occurs, increase high-speed compression damping. Air leakage often stems from faulty Schrader valves or deteriorated air seals, which should be inspected during routine service.

Unusual noises such as knocking or suction sounds usually indicate the need for a damper bleed or air spring rebuild. Misalignment of the axle or crown may cause uneven wear on stanchions and premature bushing degradation.

Performance Optimization

Advanced riders can fine-tune the Fox 40 Factory by experimenting with volume spacers in the EVOL air spring. Adding spacers increases ramp-up at the end of the stroke, providing better bottom-out resistance. Removing them offers a more linear feel, suitable for technical terrain with smaller impacts.

For coil variants, swapping spring rates allows precise tuning for rider weight and style. Using Fox’s SLS (Super Light Steel) springs reduces weight without sacrificing strength.

The GRIP2 damper provides an expansive tuning window for racers. Dialing in high-speed rebound prevents uncontrolled recovery on big hits, while low-speed rebound adjusts chassis stability during berms and slow compressions. Balancing both compression circuits enables riders to adapt to different track conditions.

Component Compatibility

The Fox 40 Factory uses a 20mm x 110mm Boost DH axle, which must be matched with compatible front hubs. The steerer tube is a 1 1/8” straight steerer, designed for dual-crown applications on downhill frames.

Brake compatibility includes post mount 203mm minimum rotors, although adapters can allow larger sizes. The fork supports both 27.5” and 29” wheel options depending on the specific model. It pairs best with high-volume downhill tires and aggressive tread patterns.

Due to its specialized use case, the 40 Factory is not ideal for trail or enduro setups. It integrates best with full DH frames and componentry designed for gravity riding, including downhill-specific stems and handlebars.

Comparison With Similar Models

Compared to the Fox 38 Factory, the 40 Factory offers a much stiffer chassis due to its dual-crown design, making it superior for downhill racing. The 38 is more versatile for enduro and aggressive trail use, with a lighter frame and single crown layout.

RockShox’s Boxxer Ultimate competes directly with the 40 Factory. While both forks feature advanced damping and full adjustability, the GRIP2 damper in the Fox fork is praised for its precise feel and high-frequency performance. Riders seeking more tunability often prefer the Fox, though the Boxxer offers slightly lower weight in air models.

The Öhlins DH38 is another competitor, known for its plush ride and coil performance. However, Fox’s wide support network and extensive tuning documentation give it an edge for racers looking to extract every ounce of performance.

Conclusion

The Fox 40 Factory represents the pinnacle of downhill suspension technology, delivering unmatched control, adjustability, and durability for elite riders. With proper installation, diligent maintenance, and tailored adjustments, this fork can significantly elevate a rider’s confidence and performance on the most demanding tracks.