RockShox Lower Leg - SID ULT 110-120
RockShox

RockShox Lower Leg - SID ULT 110-120

$320.00
In Stock

OEM replacement lower leg for RockShox SID Ultimate 110–120mm (29", 15x110 Boost). Gloss black finish with foil decals included — restores factory fit, alignment and ride quality.

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Product Details

Overview & Technology

RockShox SID ULT lower leg (Mfg. PN 11.4018.091.015, SRAM ID FS-SPP-A0) is an OEM service part designed to return your SID Ultimate 110–120mm fork to factory spec. This lower leg is the direct replacement for 2020+ SID Ultimate B4 models and comes finished in gloss black with the included foil decals for a clean, stock look. Construction uses a lightweight magnesium alloy lower casting engineered for high torsional stiffness with minimal mass — the same design priorities as the SID series: low weight, precise steering, and predictable flex characteristics. Internal reinforcements and factory-machined interfaces preserve seal geometry and damper alignment so your stanchions, seals and damper body operate as intended.

Key Features

This replacement lower leg delivers the structural and functional elements your SID needs. It includes factory brake mount bosses, sealed interfaces for dust wipers, and the axle interface machined for 15x110 Boost thru-axles. • OEM fit — manufactured to RockShox tolerances for repeatable fork performance. • Gloss black finish with foil decals included for a factory appearance. • 15x110 Boost axle interface and standard post-mount brake mounts for direct rotor alignment. • Lightweight magnesium alloy construction balances stiffness and weight for XC performance.

Fit & Compatibility

This lower leg is specified for 29" RockShox SID Ultimate forks with 110–120mm travel (B4 generation, 2020 and later). It specifically fits the 15x110 Boost thru-axle configuration — verify your axle standard before ordering. Manufacturer part number: 11.4018.091.015. SRAM Model ID: FS-SPP-A0. Please note: this listing is for a single lower leg (left or right). If you need both lowers, order two. Installation should follow RockShox service procedures — replace seals and bushings as needed and torque fasteners to factory specs. Shipping dimensions: 17.2" x 6.9" x 5.3"; weight: 1.45 lb (package).

Who This Is For

Ideal for cross-country riders, mechanics and race teams who need a direct OEM lower leg replacement to repair crash damage, wear or to refresh an aging SID Ultimate fork. If you want to retain the exact handling, brake alignment and serviceability of the factory component, this is the correct part. Also suited for bike shops and home mechanics performing fork rebuilds: the part restores the original mounting points and seal interfaces so your SID continues to perform at its lightest, most precise level.

Key Features

  • ✓ OEM RockShox lower leg for SID Ultimate 110–120mm forks
  • ✓ Fits 29" wheels with 15x110 Boost thru-axle standard
  • ✓ Gloss black finish with included foil decals for factory look
  • ✓ Lightweight magnesium alloy casting for stiffness and savings
  • ✓ Direct replacement for 2020+ SID Ultimate B4 (SRAM FS-SPP-A0)
  • ✓ Factory-machined axle, brake mount and seal interfaces
  • ✓ Sold as a single lower leg — order two for a full pair

Product Identifiers

Vendor Item # 11.4018.091.015
UPC 710845835469

Frequently Asked Questions

Is this a single lower leg or a pair?

This listing is for a single lower leg. If you need both sides of the fork, order two units. Confirm left vs. right during installation — the part is a direct OEM replacement but sold individually.

Will this fit my SID that isn't an 'Ultimate' model?

This lower leg is designed specifically for SID Ultimate B4 (2020+) 110–120mm forks. Non-Ultimate SID models or earlier generations may have different axle, brake mount, or bushing interfaces — verify model year and SRAM Model ID (FS-SPP-A0) before purchasing.

Do I need to replace seals and bushings when installing?

We recommend inspecting and replacing dust wipers, foam rings and bushings during any lower-leg service or replacement. Old seals can compromise performance and allow contamination; replacing them ensures proper fit and longevity.

Will my brake caliper and rotor remain aligned?

Yes — this is an OEM lower leg with factory-mounted brake bosses and machined interfaces to maintain rotor alignment and pad-rotor spacing when installed correctly. Always torque mounting bolts to RockShox specifications.

Can I use this on a 27.5" wheel or non-Boost axle?

No — this specific lower leg is for 29" SID Ultimate forks with a 15x110 Boost axle. If your fork uses a different wheel size or axle standard, choose the matching lower leg part designed for that configuration.

Is paint/finish durable — will decals peel?

The gloss black finish and included foil decals are factory-style. With normal riding and proper care the finish is durable, but keep in mind that rock strikes and crash damage can chip paint — decals can be re-applied or replaced if needed.

Buying Guide

When replacing a fork lower leg, match the exact model, axle standard and travel. Look up your fork's model year and SRAM/RockShox model ID to avoid fitment issues. OEM lower legs like this RockShox unit preserve factory geometry, brake alignment and seal interfaces — critical for reliable braking and suspension performance. Consider whether you need a single leg or a pair, and plan to replace seals, foam rings and bushings while you have the fork apart. If weight and stiffness are priorities, note material differences: high-end lowers use magnesium or forged aluminum to shave grams without sacrificing rigidity.

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