FOX 820-02-574-KIT Float Air Shaft 821973390529 36 NA2 140MM

( Brand: Fox ), ( Manufacturer Part Number: 820-02-574-KIT ), ( Part Type: Air Float ), ( Compatible Brand: For Fox ), ( Suspension Travel: 140 Mm ), ( Fork Type: Suspension ), ( Compatible Model: Fox 36 2021-2025 ), ( Country Of Origin: Taiwan ), ( UPC: 821973390529 )

Review FOX 36 Float Na2 Air Shaft Assembly 140mm

The **Fox 821973390529 36 Float NA2 Air Shaft (140mm, 2021 2025)** is a high-performance, precision-engineered suspension component designed to elevate the handling, comfort, and responsiveness of modern off-road and adventure vehicles. Part of Fox s advanced **NA2 (Next-Gen Air) series**, this air shaft is engineered to deliver seamless, customizable suspension tuning with unmatched reliability and durability. Built with a **36mm bore diameter**, this shaft is optimized for vehicles requiring a balance of stiffness and compliance, making it an ideal choice for everything from aggressive rock crawling to smooth overland touring. The **140mm stroke length** ensures ample travel for rough terrain while maintaining a compact, streamlined profile under the hood, minimizing interference with other components.

At the heart of this air shaft is Fox s **NA2 air spring technology**, which integrates a **high-performance air spring** with a **sealed, nitrogen-charged reservoir** to provide consistent, adjustable damping and support. The **dual-chamber design** ensures precise air pressure regulation, reducing the risk of leaks and maintaining optimal performance even under extreme conditions. The **36mm bore** strikes a perfect balance wide enough to handle high-pressure demands for aggressive off-roading while remaining compact enough to fit within tight engine bay constraints. The **2021 2025 compatibility** ensures a seamless fit for a range of modern vehicles, including popular SUVs and trucks, where Fox s reputation for innovation and durability is most valued.

One of the standout features of this air shaft is its **adjustable preload and rebound damping**, allowing riders to fine-tune the suspension to match their driving style, terrain, and load conditions. Whether you're tackling steep climbs, deep sand, or rough rock, the **NA2 air spring** delivers smooth, progressive support without the harshness of traditional coilovers. The **sealed, maintenance-free design** eliminates the need for frequent adjustments, while the **high-quality materials**, including corrosion-resistant coatings and reinforced seals, ensure longevity even in harsh environments. Additionally, the **compact, low-profile construction** makes installation straightforward, with minimal modifications required to integrate it into existing suspension setups.

For off-road enthusiasts and adventure seekers, the **Fox 821973390529** represents a leap forward in suspension technology combining Fox s legendary reliability with cutting-edge air suspension innovation. Whether you're modifying a high-end SUV for long-distance expeditions or building a rock-crawling beast, this air shaft provides the **adjustability, durability, and performance** needed to conquer any terrain. With Fox s reputation for precision engineering and a design that prioritizes both functionality and ease of use, this component is a game-changer for anyone serious about optimizing their vehicle s suspension for real-world adventure.

### **Analysis of buying a Fox 821973390529 (36 Float NA2 Air Shaft, 140mm, 2021 2025)**

This is a **Fox Float NA2 air fork** designed for **2021 2025 mountain bikes**, specifically for **20mm axle (140mm width) applications**. Below is a detailed breakdown of its **pros and cons**, followed by a **conclusion and recommendation**.

---

### **Pros**

1. **High-Quality Build**

- Fox uses **premium materials**, including **aluminum and carbon fiber components**, ensuring durability and lightweight performance.

- The **NA2 (Next-Gen Air) technology** improves efficiency, reducing pumping effort while maintaining performance.

2. **Adjustable Air Spring**

- The **adjustable air spring** allows fine-tuning of **compression and rebound** for different rider weights and terrain preferences.

- Works well for **riders weighing 120 220 lbs (54 100 kg)**, though adjustments may be needed for extreme weights.

3. **Compression Adjustment Options**

- Features **low-speed (LS) and high-speed (HS) compression damping**, allowing customization for **trail, enduro, or downhill** riding.

- The **HS compression lockout** helps with **pedaling efficiency** on climbs.

4. **Reliability & Brand Reputation**

- Fox is a **trusted brand** in the cycling industry, known for **consistent performance** and **long-term durability**.

- Widely used in **competitive and recreational riding**, reducing the risk of premature failure.

5. **Compatibility**

- Fits **2021 2025 bikes** with **140mm axle spacing**, making it a **direct replacement** for many modern hardtail and full-suspension bikes.

- Works with **standard 20mm thru-axles**, ensuring easy installation.

6. **Good for Versatile Riding**

- Performs well on **trail, cross-country, and light enduro** riding due to its **balanced tuning**.

- The **36mm travel** is sufficient for most **intermediate to aggressive trail riding**, though not ideal for extreme downhill.

7. **Warranty & Support**

- Fox offers **standard warranties** (typically 2 years), and many dealers provide **extended service plans**.

- Easily repairable and serviced at **Fox-authorized shops**.

---

### **Cons**

1. **Price Point**

- This is a **mid-to-high-end fork**, meaning it is **more expensive** than basic entry-level forks (e.g., RockShox Recon, Suntour XCR).

- Costs **$800 $1,200 ** depending on retailer and accessories (e.g., Fox Float Boost conversion kits).

2. **Weight Considerations**

- While lightweight, it is **not as ultra-light as carbon forks** (e.g., Fox 36 Float Carbon).

- The **aluminum construction** adds slight extra weight compared to full-carbon alternatives.

3. **Limited Downhill Performance**

- **36mm travel** is **not sufficient for aggressive downhill or freeride riding**, where **150mm travel** is preferred.

- May feel **stiff on rough, technical descents** compared to longer-travel forks.

4. **Maintenance Requirements**

- Like all air forks, it requires **regular servicing** (seal checks, damping adjustments, air pressure adjustments).

- **Not as low-maintenance** as coil forks (though coil forks are heavier and less efficient).

5. **Potential Pumping Effort**

- While the **NA2 air spring reduces pumping**, some riders may still find it **requires more effort than a pre-loaded coil fork**.

- Adjustments may be needed for **optimal performance**.

6. **Compatibility Issues with Older Bikes**

- **Not compatible with 9mm or 15mm axle bikes** (only 20mm).

- Some **older bikes (pre-2021)** may require **frame modifications** for installation.

7. **Learning Curve for Tuning**

- New riders may struggle with **properly setting damping and air pressure**, leading to **suboptimal performance**.

- Requires **some mechanical knowledge** to fine-tune effectively.

---

### **Conclusion**

The **Fox 821973390529 (36 Float NA2 Air Shaft, 140mm)** is a **solid, high-performance fork** suited for **trail, cross-country, and light enduro riding**. It offers **excellent adjustability, reliability, and Fox s reputation for quality**, making it a **great choice for serious riders** who want **customizable suspension without the complexity of a coil fork**.

However, it is **not ideal for extreme downhill or freeride riding** due to its **limited travel**, and it comes at a **premium price**. If you prioritize **versatility, adjustability, and Fox s engineering**, this fork is a **strong recommendation**. If you need **longer travel, lower maintenance, or a more budget-friendly option**, alternatives like the **RockShox Recon (coil) or Suntour XCR (air)** may be worth considering.

---

### **Recommendation**

You ride **trail, cross-country, or light enduro** on **2021 2025 bikes with 140mm axle spacing**.

You want **adjustable, efficient suspension** with **Fox s reliability**.

You are willing to **invest in a high-quality fork** for **long-term performance**.

You plan to **fine-tune damping** for optimal comfort and control.

You need **longer travel (150mm )** for aggressive downhill or freeride.

You prefer **lower maintenance** (coil forks like RockShox Recon).

You are on a **tight budget** (entry-level air forks like Suntour XCR may suffice).

Your bike has **9mm or 15mm axles** (this fork is **20mm only**).

This is a **top-tier fork for its category**, offering **great value for riders who need adjustability and Fox s engineering**. If it fits your riding style and bike setup, it is a **highly recommended purchase**. Otherwise, explore **longer-travel or coil alternatives** depending on your needs.

Details:

I swapped it out so she could try a longer travel. The air shaft has been cleaned with 91% improperly alcohol using Extra Alpha clean room wipes to remove all the oil and slickly. Fox Part# 820-02-574-KIT Service Set: Air Shaft Assay, 2021 36 140mm Float NA2, F-S, PS-E P-S 1.287 Bore, This was installed on my wife's fork from her full suspension bike. For sale is Fox 36 Float NA2 Air Shaft Assembly 140mm 2021 -2025.

Those came with the replacement spring. I'm happy to answer any questions so feel free message me. The included foot nut, crush washers and C-Clip ring are new/unused.

specifications ribicycl:

• brand: Fox
• mpn: 820-02-574-kit
• part type: Air Float
• compatible brand: For Fox
• suspension travel: 140 Mm
• fork type: Suspension
• compatible model: Fox 36 2021-2025
• country of origin: Taiwan
• upc: 821973390529

payments ribicycl:

• other
• credit card: Discover
• wallet: Google-pay

offer ribicycl:

• sold: 0
• options: Ship-to-home
• quantity: 1
• availability: In Stock
• started: April 26, 2026

returns ribicycl:

• policy: No Returns

general ribicycl:

• condition: Used
• Cycling > Bicycle Components Parts > ks

seller ribicycl:

• city: Warrenville, Illinois
• # reviews: 978
• rating: 100.0%

shipping ribicycl:

• transit: 4-6 Days
• type: Fixed
• class: Standard
• cost: $0.00
• service: Standard

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