Freehub compatibility: HG, XDR & Micro Spline | Competitive Cyclist

What does cassette-to-freehub compatibility mean?

Cassette-to-freehub compatibility describes whether a cassette's spline pattern and overall stack length will properly mate with a hub's freehub body. Common modern standards are Shimano/SRAM HyperGlide (HG), SRAM XDR (road 12-speed), and Shimano Micro Spline (12-speed MTB). If the cassette and freehub body don't match, the cassette won't install, or worst case, it won't lock securely.

Why It Matters

Fitment affects shifting precision, drivetrain life, and the ability to run the cassette spec you want (smallest cog size, range). A mismatched cassette can leave you stranded before a KOM attempt or force an awkward parts swap the night before a club ride.

Short lead-in line.

Bike cassettes & cogs — Find cassettes by spline standard and gear range
Road bike cassettes — Road 12-speed options that may need XDR drivers
Hubs & skewers — Confirm which driver body your hub accepts
Tools & maintenance — Shop tools for swapping drivers and lockrings

How It Works

Think of the freehub body as a splined socket and the cassette as the matching plug. Compatibility has two dimensions:

Spline pattern: tooth shape and count on the hub; HG, XDR, and Micro Spline each have incompatible spline geometries.
Effective stack length (axial position): the distance from the hub shoulder to the end of the freehub. This determines where the smallest cog sits and whether the lockring can clamp properly.

Diagram concept: imagine three side-by-side cross-sections of a hub body showing different spline profiles and a cassette slid on until the lockring engages. The Micro Spline profile is finer and allows a 10-tooth smallest cog; HG uses a wider spline intended historically for 11T minimum; XDR shifts the cassette slightly inward compared to standard HG to accommodate SRAM road 12-speed cassettes.

Practical hub architecture: many modern hubs (DT Swiss, Hope, Industry Nine) use interchangeable driver bodies. Swapping a driver body is the usual fix for compatibility: remove axle endcaps, pull the driver off, press on the XDR or Micro Spline driver. Always check the hub manufacturer's procedure and required tools.

Inline resources: check your hub's product page in Hubs & skewers to confirm which drivers are supported, and compare candidate cassettes in Bike cassettes & cogs for spline type.

> Pro tip: Don’t assume an 11-speed cassette fits every HG body. Confirm the cassette spec and the hub driver before you buy.

Key Specs/Thresholds

HG (HyperGlide): standard spline used by Shimano and many SRAM cassettes; historically supports 8–11 speed road/cassette families and some 12-speed SRAM via XDR variants. Typical smallest cog compatibility: commonly 11T on traditional HG cassettes.
XDR (SRAM road 12-speed driver): a narrower/shorter-driver profile for SRAM road 12-speed cassettes. XDR is not the same spline as Micro Spline or XD; it’s intended for road 12s that require reduced stack length.
Micro Spline (Shimano 12-speed MTB): proprietary Shimano spline designed to allow a 10T smallest cog on 12-speed MTB cassettes (XT/XTR/Deore). Micro Spline is incompatible with HG and XDR splines.
Interchangeability: many hubs offer driver bodies you can swap; expect to add 30–120 g depending on design and spare driver weight.

Common Misconceptions

You can force-fit different cassettes: false. Different splines won't seat and forcing risks damage.
Spacer solves every problem: sometimes a spacer helps axial position, but it doesn't change spline geometry. You cannot use a spacer to adapt HG splines to Micro Spline or XDR.
All 12-speed is the same: not true. Shimano 12-speed MTB uses Micro Spline; SRAM 12-speed road uses XDR; SRAM 12-speed MTB uses XD—three different ecosystems.

When to Choose/Use

If you're buying Shimano 12-speed MTB cassettes (XTR/XT/SLX 12s), choose a hub or driver body that supports Micro Spline.
If you're fitting SRAM AXS or other SRAM road 12-speed cassettes, check if they require XDR. Many modern road 12s need XDR drivers.
If you're running 11-speed or older 10-speed cassettes, a standard HG freehub body is usually fine.
Want to upgrade wheels but keep your cassette? Confirm the replacement wheel's driver-body options or budget for a driver swap.

Sources

SRAM (2016) — XDR and driver-body explanations and product pages
Shimano (2019) — Micro Spline technical info and cassette compatibility notes
Park Tool (2020) — Cassette removal and freehub body basics
Wheels Manufacturing (2018) — Interchangeable driver bodies and adapters

Related Categories

Key Takeaways

HG, XDR, and Micro Spline are different splines and stack profiles — not interchangeable.
Micro Spline enables a 10T smallest cog on Shimano 12-speed MTB cassettes.
XDR is SRAM's road 12-speed driver with a reduced stack length compared to standard HG.
Many hubs accept interchangeable driver bodies; swapping is the common compatibility fix.

FAQs

Can I swap my hub's driver body at home?

Often yes—many hubs (DT Swiss, Hope, Industry Nine) use removable drivers. You need the manufacturer's procedure, basic tools, and clean grease. If the hub is sealed or the driver seems press-fit, have a shop handle it.

Will a spacer let me run a Micro Spline cassette on an HG body?

No. A spacer can change axial position but cannot change the spline geometry. Micro Spline cassettes require a Micro Spline driver body.