The Fox 38 Rhythm suspension fork is engineered to deliver high performance for aggressive trail and enduro mountain biking. Positioned as the entry-level version within the Fox 38 series, the Rhythm variant prioritizes accessibility without compromising on durability or essential performance features. This guide provides an in-depth technical breakdown of the 38 Rhythm’s installation, tuning, and upkeep, as well as its suitability compared to other suspension fork options.
Tools Required
- 6mm and 8mm Allen keys [paid link]
- Torque wrench [paid link] (Nm scale)
- Crown race setting tool
- Shock pump
- Suspension grease (e.g., Fox Float Fluid)
- Ruler or sag measurement tool
- Clean rags and isopropyl alcohol
- Lower leg removal tools (for service)
Installation Guidelines for the Fox 38 Rhythm
Correct installation is crucial for both safety and performance. The Fox 38 Rhythm features a 1.5″ tapered steerer and 15mm x 110mm Boost axle spacing. Always check frame compatibility before proceeding.
Begin by inserting the steerer tube through the head tube and aligning headset components. Use a torque wrench [paid link] to tighten the stem bolts to the manufacturer’s specifications, typically around 5–6 Nm. The crown race must be properly seated using a crown race setting tool. Ensure the front wheel fits snugly into the Boost axle and torque the axle to 19.7 Nm.
It’s also essential to verify that brake calipers align accurately with the 180mm post-mount brake tab. If your rotor size differs, install the appropriate brake adapter to avoid misalignment.
Initial Setup and Adjustment
Suspension setup begins with sag. Fox recommends setting sag at 15–20% of the fork’s travel. For the 38 Rhythm’s standard 160mm travel, this translates to 24–32mm of sag. Riders should adjust air pressure via the EVOL air spring, using the shock pump and Fox’s air pressure chart based on rider weight.
The GRIP damper in the 38 Rhythm features a sweep-adjustable low-speed compression dial and a rebound adjustment at the fork leg base. Turn both dials fully clockwise to close, then back them off counterclockwise to reach base settings. Typically, rebound is set faster for lighter riders and slower for heavier or more aggressive riders.
Maintenance Intervals and Procedures
Routine maintenance extends the lifespan of the fork and preserves performance. Every 30 hours of riding, clean the stanchions and check for oil residue or dirt intrusion. Apply a few drops of suspension lubricant around the dust seals and cycle the fork to maintain seal health.
A full lower leg service is recommended every 50 hours. This involves removing the lower legs, draining the bath oil, and inspecting foam rings and dust wipers for contamination or wear. Re-lubricate the foam rings with suspension grease and reinstall using fresh bath oil (20ml per leg).
Annually, or after approximately 125 hours of riding, a damper and air spring service should be performed. This involves disassembling internal components and replacing o-rings, seals, and fluid.
Troubleshooting Common Set-Up Issues
Excessive dive under braking: This typically results from insufficient air pressure or too little low-speed compression damping. Increase air pressure by 5–10 psi and add 2–3 clicks of compression damping.
Harsh bottom-outs: Indicates inadequate progression in the air spring. Adding volume spacers into the air chamber increases bottom-out resistance. The 38 Rhythm accepts up to 5 volume spacers, depending on rider weight and riding style.
Fork not returning smoothly: Check rebound settings and inspect for contamination or inadequate lubrication. If issues persist, a lower leg service is recommended.
Customization and Performance Optimization
The Fox 38 Rhythm offers several avenues for customization. The air spring can be tailored using volume spacers, providing tunable ramp-up characteristics. For heavier or more aggressive riders, increasing ramp-up helps maintain support through rough terrain.
The GRIP damper, while simpler than the GRIP2, provides sufficient tuning range for trail and enduro riding. Riders seeking finer high-speed compression and rebound control might consider upgrading to a GRIP2 damper, though this requires advanced mechanical skills and additional cost.
Upgrading seals to low-friction SKF versions can also reduce breakaway force and improve small bump compliance. Additionally, installing a bolt-on fender helps protect the stanchions from debris and extends service intervals.
Compatibility with Drivetrain and Frame Standards
The 38 Rhythm uses standard Boost spacing (15x110mm), ensuring compatibility with most modern trail and enduro frames. It supports rotor sizes from 180mm to 203mm with appropriate adapters. The fork is designed around a 29” or 27.5” wheel size, depending on the specific model configuration.
The steerer tube is 1.5″ taper, which aligns with almost all contemporary mountain bike frames. The fork is not compatible with dual crown or inverted setups, nor is it designed for cross-country applications due to its weight and stiffness.
Comparison with Other Forks in the Fox Lineup
The Fox 38 Rhythm is distinguished by its sturdy 38mm chassis and GRIP damper. Compared to the Fox 38 Performance and Factory series, the Rhythm uses a slightly heavier chassis and lacks the GRIP2 damper found in higher-end models.
However, the core performance remains strong. Riders will find the same chassis stiffness and EVOL air spring, making it a formidable fork for aggressive riders on a budget. The lack of Kashima coating means marginally higher stiction, but not significantly enough to affect real-world performance for most riders.
Compared to the Fox 36 series, the 38 Rhythm provides more stiffness and better heat dissipation for long, rough descents. Riders focused on bike park or enduro racing will benefit from the added robustness.
FAQs
Is the Fox 38 Rhythm suitable for downhill riding?
While not a dedicated downhill fork, the 38 Rhythm performs well in enduro and aggressive trail settings, including park riding. However, riders requiring double-crown stiffness should consider a DH-specific fork.
Can I upgrade the GRIP damper to a GRIP2?
Yes, the GRIP damper can be swapped for a GRIP2 unit, provided the chassis is compatible. This upgrade offers enhanced control over high- and low-speed compression and rebound.
How often should I service the Fox 38 Rhythm?
Basic maintenance like cleaning and lubrication should be done every 30 hours. Lower leg services are recommended every 50 hours, and full overhauls every 125 hours.
What wheel sizes does the 38 Rhythm support?
It is available in both 27.5” and 29” configurations. Riders must ensure their fork matches the wheel diameter of their bike.
Can I use the 38 Rhythm with a non-Boost hub?
No, the 38 Rhythm is designed exclusively for Boost spacing (15x110mm). Non-Boost hubs are incompatible without unsafe adapters.
Is the 38 Rhythm too heavy for trail use?
It is heavier than Fox’s 34 or 36 series, but the added stiffness and support are well-suited for aggressive trail riders who prioritize control over minimal weight.
Conclusion
The Fox 38 Rhythm stands out as one of the best value performance suspension forks for aggressive mountain biking. With a robust chassis, tunable air spring, and simple yet effective GRIP damper, it balances affordability with high-end function. Though it lacks the refinements of premium models, its ride quality and upgrade potential make it a top choice for trail and enduro riders seeking dependable performance without the premium price tag.