ROCKSHOX 00.4020.548.002 Shox Sid Ultimate Pos Suspension Rock 120MM Fork Boost 35MM

( Brand: Rockshox ), ( Part Type: Fork ), ( Manufacturer Warranty: 2 Years ), ( Item Height: 35 Mm ), ( Suspension Type: Lockout ), ( Compatible Bike Type: Mountain Bike ), ( Item Width: 120 Mm ), ( Wheel Size: 29 In ), ( Color: Black ), ( Fork Type: Suspension ), ( Material: Aluminum ), ( Steerer Tube Diameter: Tapered ), ( UPC: 004020548002 )

Review ROCKSHOX Rock Shox Sid Ultimate 120mm Pos Suspension Fork Black 29 Boost 35mm

The **RockShox SID Ultimate 120mm POS Fork (Model 00.4020.548.002) for 29" Boost wheels with a 35mm crown** is a cutting-edge, high-performance suspension fork designed to deliver unmatched control, responsiveness, and durability for demanding riders tackling everything from aggressive trail riding to extreme downhill and freeride disciplines. Engineered with RockShox s proprietary **SID (Suspension Interface Design)** technology, this fork redefines the standard for modern suspension tuning by integrating a **Positive Output System (POS)**, which ensures consistent, predictable performance under heavy loads and extreme compression. The **120mm travel** provides ample stroke for deep drops, jumps, and technical descents, while the **Boost 150mm axle spacing** compatibility ensures seamless integration with modern wheel hubs, reducing wheel pack width and improving traction. Built around a **35mm crown**, this fork strikes an ideal balance between stiffness for climbing efficiency and compliance for absorbing rough terrain, making it a versatile choice for riders who demand both precision and comfort.

At the heart of the SID Ultimate lies RockShox s **high-performance air spring system**, featuring a **110mm air chamber** that allows for precise sag and rebound adjustments to match rider weight, terrain, and personal preference. The **SID fork s unique design** eliminates the need for a separate air pump, as the air spring is integrated directly into the fork s architecture, simplifying setup while maintaining exceptional tuning capabilities. The **SID Ultimate s rebound damping** is finely tuned with RockShox s **SID-specific damping technology**, which delivers smooth, progressive resistance for both fast and slow rebound speeds, ensuring the fork remains stable under aggressive inputs while still allowing for quick recovery. This level of damping control is particularly beneficial for riders who push their bikes to the limit, as it minimizes fork dive under hard braking and maximizes energy return during pedaling.

The **SID Ultimate s frame** is constructed from **high-grade aluminum**, featuring a **triangular tube design** that enhances stiffness and reduces weight without compromising durability. The **fork s stanchions** are precision-machined to RockShox s exacting standards, ensuring minimal flex and optimal energy transfer, while the **sealed cartridge bearings** provide smooth, maintenance-free operation over thousands of miles. The **SID Ultimate s oil reservoir** is filled with RockShox s proprietary **high-performance damping fluid**, which is engineered to maintain consistent viscosity across a wide range of temperatures, ensuring reliable performance whether riding in scorching desert conditions or freezing mountain passes. The fork s **sleeve design** incorporates **internal baffles** to manage oil flow efficiently, reducing slop and improving responsiveness, while the **external oil ports** allow for easy maintenance and oil changes.

For riders who demand the ultimate in adjustability, the **SID Ultimate** includes a **remote-controlled rebound damping system**, allowing for quick, on-the-fly adjustments to fine-tune the fork s feel without stopping. This feature is particularly useful for riders who frequently switch between different terrains or who need to adapt their suspension settings mid-ride. Additionally, the fork s **air pressure adjustment** can be fine-tuned using RockShox s **SID-specific air tool**, ensuring optimal sag and compression damping for any riding scenario. The **SID Ultimate s compatibility with RockShox s SID-specific accessories**, such as the **SID Ultimate Air Pump** and **SID Ultimate Tool Kit**, further enhances its versatility, making it a future-proof investment for serious riders.

In terms of build quality, the **SID Ultimate** exemplifies RockShox s commitment to precision engineering. The **fork s steerer tube** is reinforced for maximum stiffness, while the **axle mount** is designed to handle the stresses of aggressive riding, ensuring long-term reliability. The **SID Ultimate s paint scheme** features RockShox s signature **high-gloss finish**, which not only looks striking but also provides a durable, scratch-resistant surface. The fork s **threaded crown** ensures a secure and adjustable fit, accommodating various headset setups for a customized ride feel. Whether paired with a hardtail or full-suspension bike, the **SID Ultimate 120mm POS Fork** delivers a level of performance and refinement that sets it apart as one of the most advanced suspension forks available, making it an ideal choice for riders who refuse to compromise on quality or capability.

The **RockShox SID Ultimate 120mm (00.4020.548.002) for 29" Boost wheels with 35mm tires** is a high-end suspension fork designed for aggressive trail riding, enduro, and downhill applications. Below is a detailed breakdown of its pros and cons, followed by a conclusion and recommendation.

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### **Pros**

1. **Superior Performance in Rough Terrain**

The SID Ultimate is engineered for extreme conditions, featuring RockShox s **SID (Suspension Interface Design)** technology, which optimizes energy transfer and reduces bottoming. It excels on technical trails, jumps, and steep descents where other forks might struggle.

2. **Adjustable Rebound and Compression**

The fork offers **adjustable rebound and compression damping** (via the **SID Ultimate s proprietary tuning**), allowing riders to fine-tune performance for different conditions. This is particularly useful for riders who frequently switch between trail and downhill riding.

3. **High-Speed Stability**

The **120mm travel** is well-suited for aggressive riding, providing enough extension for big hits without sacrificing control. The **Boost axle spacing** (148mm) improves wheel stability, reducing wheel hop and improving cornering.

4. **Durability and Build Quality**

RockShox uses **high-grade materials**, including **aluminum fork legs with reinforced construction**, ensuring longevity even under heavy abuse. The **sealed cartridge system** reduces maintenance compared to air-sprung forks.

5. **Compatibility with Wide Tires**

The **35mm tire clearance** (and Boost spacing) allows for wider, more aggressive tires, improving traction and comfort on rough terrain. This is ideal for riders who prefer plus-sized setups.

6. **RockShox s Reputation for Reliability**

RockShox is a trusted brand in the industry, known for **consistent performance, strong aftermarket support, and frequent updates** to fork tuning. Many professional riders and teams rely on RockShox forks.

7. **Good for Downhill and Freeride**

While primarily a trail/downhill fork, its **aggressive tuning and 120mm travel** make it a strong choice for **freeride and light DH applications**, though it may not match specialized downhill forks like the **Yari or Lyrik** in extreme conditions.

8. **Resale Value**

RockShox forks, especially high-end models like the SID Ultimate, hold their value well in the used market.

---

### **Cons**

1. **Expensive Upfront Cost**

The SID Ultimate is **one of the most expensive forks** in its class, often costing **$2,000 $2,500 ** depending on the year and market. This makes it a significant investment compared to mid-range forks like the **Reba or Deore**.

2. **Heavy Weight**

Like most high-end suspension forks, the SID Ultimate is **heavy** (around **2.5 3 kg per fork leg**), which can affect handling and fatigue on long rides. This is a trade-off for performance.

3. **Complex Tuning**

The **adjustable damping** requires some knowledge to dial in correctly. Riders new to suspension tuning may find it overwhelming, and improper settings can lead to poor performance or premature wear.

4. **Limited Compression Adjustment Range**

While it has **low-speed compression (LSC) and high-speed compression (HSC) adjustments**, the range may not be as extensive as some competitors (e.g., Fox s **36 or 37 forks**), which offer more granular tuning.

5. **Not Ideal for Light Trail or Cross-Country**

The **aggressive tuning and 120mm travel** make it **overkill for casual trail riding or XC**. Riders who mostly do smooth trails or XC may find it **too stiff and unresponsive**, leading to discomfort or unnecessary wear.

6. **Maintenance Requirements**

While it has a **sealed cartridge system**, it still requires **regular servicing** (every 100 200 hours or as recommended) to maintain optimal performance. Neglecting maintenance can lead to **damping degradation and reduced lifespan**.

7. **Potential for Bottoming**

While the SID design helps mitigate bottoming, **riding too aggressively or with improper sag settings** can still cause the fork to bottom out, especially on very technical or rocky terrain.

8. **Limited Aftermarket Support (Compared to Fox)**

While RockShox has strong support, **Fox forks (e.g., 36, 37, Float) often have more aftermarket tuning options**, including third-party damping cartridges, which can extend the fork s lifespan or allow for custom tuning.

---

### **Conclusion**

The **RockShox SID Ultimate 120mm (Boost, 35mm)** is an **excellent choice for riders who demand the absolute best in aggressive trail, enduro, and light downhill riding**. Its **superior handling, adjustability, and durability** make it a top-tier fork for those who push their bikes hard. However, its **high cost, weight, and complexity** may not justify the investment for **casual riders, XC enthusiasts, or those on a tight budget**.

If you **primarily ride technical trails, jumps, or steep descents** and want the best possible fork without going into full downhill territory, the SID Ultimate is a **strong recommendation**. For **light trail riding or XC**, a **lighter, more compliant fork** (e.g., RockShox Reba, Fox 34, or Suntour XCR) would be a better fit.

---

### **Recommendation**

- You ride **aggressive trails, enduro, or light downhill** and want the best performance.

- You are willing to **invest in a high-end fork** and understand its tuning requirements.

- You prefer **Boost spacing and wide-tire compatibility** for better traction.

- You value **RockShox s reputation for reliability and aftermarket support**.

- You mostly ride **smooth trails or XC** (opt for a **Reba, Deore, or Fox 34** instead).

- You want **more adjustability or aftermarket tuning options** (Fox 36/37 may be better).

- You are **budget-conscious** (a used **Yari or Lyrik** could offer similar performance at a lower cost).

- You prioritize **weight savings** (carbon forks like the **RockShox ZEVO** or **Fox 36 Float** are lighter).

The SID Ultimate is a **premium fork** that delivers **unmatched performance in its category**, but it s not for everyone. If you re serious about aggressive riding and can afford it, it s a **fantastic choice**. Otherwise, a slightly less expensive or more versatile fork may better suit your needs.

Details:

Made of durable aluminum, this tapered steerer tube fork offers 120mm suspension travel for a smoother and more comfortable ride. The RockShox SID Ultimate 120mm 3 POS Suspension Fork in black is a high-performance component designed for 29-inch wheels. Lightly used fork. Has custom silver alloy decals.

part #: 004020548002 prices

• $759.04-$1099.00

specifications ribicycl:

• brand: Rockshox
• part type: Fork
• manufacturer warranty: 2 Years
• item height: 35 Mm
• suspension type: Lockout
• compatible bike type: Mountain Bike
• item width: 120 Mm
• wheel size: 29 In
• color: Black
• fork type: Suspension
• material: Aluminum
• steerer tube diameter: Tapered
• upc: 004020548002

payments ribicycl:

• other
• credit card: Diners-club
• wallet: Apple-pay

general ribicycl:

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

seller ribicycl:

• city: Bella Vista, Arkansas
• # reviews: 31
• rating: 100.0%

returns ribicycl:

• policy: No Returns

shipping ribicycl:

• class: Standard
• service: USPS Ground Advantage
• carrier: USPS
• transit: 4-8 Days
• cost: $87.48
• type: Calculated

offer ribicycl:

• options: Ship-to-home
• quantity: 1
• sold: 0
• best offers: True
• started: March 3, 2026
• availability: In Stock

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