The Fox 40 Factory is an elite-level downhill fork designed to meet the highest standards of trail performance, durability, and adjustability. Developed for aggressive riders and World Cup-level racing, this fork integrates Fox’s advanced technologies, including the GRIP2 damper and Float EVOL air spring. Understanding how to install, tune, and maintain the 40 Factory is essential for unlocking its full potential on technical descents and demanding terrain. This guide walks through every crucial aspect of the Fox 40 Factory to help both home mechanics and pro-level riders.
Tools Required
- 5 mm and 6 mm hex wrenches
- Torque wrench [paid link] with Nm scale
- Crown race setting tool
- Cassette tool (for axle removal)
- Suspension pump (accurate to 300 psi)
- Oil level syringe or digital caliper [paid link]
- Shock oil (Fox 20wt Gold or specified)
- Clean microfiber cloths
- Isopropyl alcohol (for cleaning stanchions and seals)
- Grease (suspension-specific)
Installation of the Fox 40 Factory
The Fox 40 Factory requires a dual crown setup, making the installation more specialized than single crown forks. Begin by verifying your frame’s head tube compatibility and ensuring a proper downhill headset is installed. Slide the steerer tube through the head tube, aligning the crowns parallel. Use a torque wrench [paid link] to tighten the upper and lower crown bolts evenly, following Fox’s torque specification (generally 5.1 Nm for crown pinch bolts).
Install the crown race securely using a setting tool, and ensure the steerer tube length is cut with enough clearance for stem clamping. The axle, being a pinch-bolt style with floating axle technology, should also be torqued evenly to prevent fork leg misalignment. Use a cassette tool if necessary to remove or install the axle cap.
Initial Setup and Adjustment
The 40 Factory is designed with a Float EVOL air spring in the left leg and a GRIP2 damper in the right. Riders should first set sag using body weight—typically aiming for 20-25% of fork travel. Using the suspension pump, adjust air pressure based on rider weight and riding style, referencing Fox’s setup chart for baseline settings.
The GRIP2 damper offers high-speed and low-speed compression and rebound adjustments. Begin with all dials set to the recommended neutral position and incrementally adjust after test rides. Low-speed settings influence mid-stroke support and cornering; high-speed adjustments affect big hit compliance.
Routine Maintenance Requirements
Maintaining the Fox 40 Factory ensures its longevity and performance. Clean the stanchions after every ride using a microfiber cloth and isopropyl alcohol. Every 30 hours, perform a lower leg service to replace oil and inspect seals. This includes removing the lowers, draining the oil, and refilling with Fox 20wt Gold suspension fluid. Seals should be lubricated lightly with suspension grease before reinstallation.
After 125 hours or annually, conduct a full damper and air spring service. This process requires disassembling both legs, bleeding the damper, and refreshing internal o-rings. Fox provides service kits that match this schedule precisely.
Troubleshooting Common Setup Issues
Some riders report initial stiffness or poor small-bump sensitivity. This often results from incorrect air pressure or poor rebound tuning. Ensure the EVOL negative air spring is fully equalized by compressing the fork after inflating. Slow rebound can also hinder sensitivity—adjust rebound toward the faster side and re-test.
Misaligned fork legs, caused by improper axle torque, can result in binding. To resolve, loosen axle and pinch bolts, compress the fork several times, and re-tighten uniformly. If creaking is heard from the crown, inspect the steerer tube interface and torque the crown bolts evenly.
Customization and Performance Optimization
The 40 Factory allows deep customization through volume spacers in the air spring. Adding spacers increases progression for more end-stroke support; removing them creates a more linear feel. Adjust this based on whether you’re racing steep tracks or riding bike park laps.
For damping, track-specific tuning is beneficial. Technical and root-heavy trails benefit from reduced high-speed compression for better traction. Conversely, flow trails allow for firmer settings. High-speed rebound should be balanced with compression changes to prevent packing.
Compatibility with Other Drivetrain and Frame Components
The Fox 40 Factory is designed for DH-specific frames with a 1.125” to 1.5” tapered head tube and 20 mm thru-axle dropouts. It’s compatible with 29” and mixed-wheel configurations, depending on the model year. Ensure your brake caliper uses the correct 200 mm or 203 mm post-mount standard. Torque cap-compatible hubs improve stiffness when used with the 40’s dropout design.
It is not designed for trail or enduro bikes due to its stiffness, axle-to-crown height, and travel (typically 203 mm). For drivetrain integration, verify that front brake hose routing allows full fork compression without kinks or snags.
Model Comparison: 40 Factory vs. 40 Performance Elite
The 40 Factory and 40 Performance Elite share the same chassis and GRIP2 damper. However, the Factory version includes Kashima-coated stanchions, which reduce friction and improve durability. For riders focused on competitive edge and responsiveness, the Factory is the superior choice. The Performance Elite offers near-identical performance but sacrifices long-term surface slickness and micro-vibration damping.
Both models offer equal tunability, though the Factory’s stanchion finish makes it more resistant to wear and environmental damage over time.
FAQs
What is the recommended air pressure for the Fox 40 Factory fork?
Refer to Fox’s pressure chart based on your weight. As a general rule, start with 1 psi per pound of rider weight and fine-tune based on sag measurements.
Can I run the 40 Factory on a trail or enduro bike?
No. The 40 is a dual-crown downhill fork with geometry suited for DH frames only.
How often should the 40 Factory be serviced?
Perform a lower leg service every 30 hours and a full service every 125 hours or annually.
Why is my Fox 40 fork feeling harsh on small bumps?
Check for correct negative spring equalization, air pressure, and rebound settings. Also inspect for fork leg binding.
Is the GRIP2 damper better than FIT4 for downhill riding?
Yes. GRIP2 provides independent high/low-speed adjustments, ideal for high-speed impacts and technical terrain.
What is the purpose of the floating axle system?
It helps align the fork legs and reduces friction, improving small bump sensitivity and responsiveness.
Conclusion
The Fox 40 Factory sets the benchmark for downhill forks by combining precise adjustability, durable construction, and advanced damping technology. Whether you’re tuning for a World Cup track or upgrading your park bike, the 40 Factory offers the performance edge necessary for aggressive, high-speed riding. By following proper installation, setup, and maintenance protocols, riders can fully leverage the fork’s capabilities and extend its service life with confidence.