Specialized Chisel / Epic Alloy Complete Headset ZS44/ZS56 OEM

Specialized Chisel / Epic Alloy Complete Headset

Factory OEM | ZS44 / ZS56 Zero Stack | 1-1/8" to 1.5" | S182500004

The Specialized Factory Replacement Chisel / Epic Alloy Complete Headset is a genuine OEM Zero Stack press-fit headset assembly for compatible Specialized Chisel and Epic alloy mountain bikes.

The complete kit includes the ZS44 upper cup, ZS56 lower cup, upper and lower angular-contact bearings, flush top cover, split compression ring, and split alloy crown race required to restore the original headset configuration.

While the original product description references 2018–2025 Chisel and 2018–2019 Epic Alloy, the supplied OEM compatibility data extends Chisel use through 2027 and lists additional Epic applications through 2021. The detailed OEM list below has therefore been preserved as the primary fitment reference.

Available from Stage 21 Bikes, your trusted source for hard-to-find Specialized OEM replacement parts.

Key Features

• Genuine Specialized factory OEM complete headset
• Zero Stack press-fit design
• ZS44 upper headset cup
• ZS56 lower headset cup
• 1-1/8" upper bearing
• 1.5" lower bearing
• 45° × 45° upper and lower bearing angles
• 48mm OD flush top cover
• Split plastic compression ring
• Split 1.5" alloy crown race
• Designed for compatible Chisel and Epic alloy frames
• Specialized MPN S182500004

Kit Includes

• 1 × ZS44 Upper Press-Fit Cup
• 1 × Upper Headset Bearing
• 1 × ZS56 Lower Press-Fit Cup
• 1 × Lower Headset Bearing
• 1 × 48mm Flush Top Cover
• 1 × Split Plastic Compression Ring
• 1 × Split 1.5" Alloy Crown Race

Specifications

Bearing Details

Upper Headset

• Zero Stack ZS44 press-fit cup
• Bearing: 41.8mm OD × 30.5mm ID × 6.5mm
• Contact angle: 45° × 45°
• Designed for 1-1/8" upper steerer interface

Lower Headset

• Zero Stack ZS56 press-fit cup
• Bearing: 52mm OD × 40mm ID × 7mm
• Contact angle: 45° × 45°
• Designed for 1.5" lower steerer interface

OEM Compatibility

2027

• Chisel Comp
• Chisel

2026

• Chisel Hardtail
• Chisel Frameset
• Chisel Comp
• Chisel

2025

• Chisel Shimano
• Chisel Hardtail Frameset
• Chisel Hardtail Comp
• Chisel Hardtail
• Chisel Frameset
• Chisel Comp Shimano
• Chisel Comp EVO
• Chisel Comp
• Chisel

2024

• Chisel Hardtail Comp
• Chisel Hardtail

2023

• Chisel Hardtail Frameset
• Chisel Hardtail Comp
• Chisel Hardtail

2022

• Chisel Hardtail LTD Frameset
• Chisel Hardtail Frameset
• Chisel Hardtail Comp
• Chisel Hardtail

2021

• Epic EVO
• Chisel LTD Frameset
• Chisel Frameset
• Chisel Comp
• Chisel

2020

• Epic Comp EVO
• Epic Comp
• Chisel Frameset
• Chisel Comp
• Chisel

2019

• Women's Epic Comp Alloy
• Women's Chisel Expert
• Women's Chisel Comp
• Men's Epic Comp Alloy
• Men's Chisel Expert
• Men's Chisel Comp X1
• Men's Chisel Comp
• Epic Comp EVO
• Chisel Frame

2018

• Women's Epic Comp Alloy
• Women's Chisel Expert
• Women's Chisel Comp
• Men's Epic Comp
• Men's Chisel Frameset
• Men's Chisel Expert – 2x
• Men's Chisel Expert – 1x
• Men's Chisel Comp

Installation Notes

• This is a press-fit Zero Stack headset and requires proper headset cup installation tools.
• Confirm that the frame uses ZS44 upper and ZS56 lower headset interfaces before installation.
• The split alloy crown race installs at the fork's 1.5" crown interface.
• Install the bearings with the correct 45° × 45° orientation.
• Headset preload and stem hardware should be adjusted according to Specialized service specifications.

Compatibility Notes

• The supplied OEM data shows compatibility across 2018–2027 Chisel applications.
• The supplied OEM list also includes Epic / Epic EVO applications from 2018 through 2021, which is broader than the shorter 2018–2019 Epic Alloy summary.
• Because Specialized headset configurations can vary by frame generation, confirm MPN S182500004 and the ZS44 / ZS56 cup dimensions before ordering.
• Compatible applications use a 1-1/8" upper and 1.5" lower tapered steerer configuration.
• This listing is for the complete headset assembly, not bearings alone.

Complete Factory Headset Replacement

Unlike individual bearing kits, Specialized S182500004 includes the cups, bearings, compression ring, top cover, and crown race needed for a more complete headset rebuild.

The factory ZS44 / ZS56 Zero Stack configuration restores the intended fit, bearing alignment, and steering interface on compatible Specialized Chisel and Epic alloy frames.

Stage 21 Bikes carries genuine Specialized factory replacement parts and hard-to-find OEM service components for current and previous-generation mountain bikes.