Definition
HG, XDR and Micro Spline are three incompatible freehub-body standards. Each defines spline shape and spacing that a cassette slides onto. HG (HyperGlide) covers most 8–11-speed cassettes. SRAM’s XDR is a narrower driver for modern 12-speed road cassettes with a 10‑tooth small cog. Shimano’s Micro Spline is a unique spline for Shimano 12‑speed MTB cassettes that also accepts a 10T cog.
Why It Matters
A mismatched freehub body means the cassette won't seat or lock, which affects shifting, safety and wheel rebuild options. Correct fit influences smallest-cog availability (10T vs 11T), gear range, and whether you can reuse your wheel with a new drivetrain.
Related Categories
Quick links to parts that matter when you change freehub bodies.
Bike cassettes & cogs — Choose cassettes that match your freehub spline and speed.
Wheels — Wheel hubs determine whether you can swap a freehub body.
Hubs & skewers — Verify replaceable freehub options and endcap fits.
Road bike hubs — Road hubs often support XDR or HG drivers.
Drivetrain small parts — Lockrings, spacers and endcaps are part of the compatibility puzzle.
How It Works
At its simplest, a freehub body is a splined stub on the hub. The cassette slides on and a lockring compresses it into place.
HG (Shimano HyperGlide): a long‑standing spline profile used for most 8–11 speed Shimano and SRAM cassettes. It does not accept 10T smallest cogs reliably. If your cassette is 11–32 or similar, it likely uses HG.
XDR (SRAM): an alloy driver that is narrower than HG to position a 10T cog correctly for SRAM road 12‑speed cassettes (e.g., SRAM Red AXS). Hubs that accept XDR typically list XDR compatibility or ship with an XDR body installed.
Micro Spline (Shimano): a different spline geometry introduced to allow Shimano 12‑speed MTB cassettes with a 10T cog while preserving cassette spacing and chainline. Micro Spline is not HG compatible; you cannot mount a Shimano 12‑speed MTB cassette on an HG body.
Conceptual diagram (visualize): hub shell -> removable freehub body (HG/XDR/Micro Spline) -> cassette splines -> lockring. On many hubs the freehub body is removable and serviceable; the correct endcaps and axle setup are critical.
Pro tip: If you’re unsure whether a hub supports a freehub swap, check the hub spec or consult a shop tech. Some budget hubs use non‑serviceable drivers.
Key Specs/Thresholds
Speed compatibility:
HG: typically 8–11 speed cassettes.
XDR: SRAM road 12‑speed cassettes (10T smallest cog).
Micro Spline: Shimano 12‑speed MTB cassettes (10T smallest cog).
Smallest cog supported:
HG: generally 11T minimum (varies by cassette design).
XDR: supports 10T road cassettes.
Micro Spline: supports 10T MTB cassettes.
Common cassette lockring torque: ~40 Nm (check manufacturer spec for exact values).
Freehub service notes: many high‑end hubs use removable bodies that weigh ~40–120 g depending on material (aluminum vs steel). Replacing a freehub body is usually a 10–30 minute shop job with 5mm hex or T25 required on some models.
Common Misconceptions
You can fit any 12‑speed cassette on any freehub. False — Shimano 12‑speed MTB and SRAM 12‑speed road use different bodies.
An adapter will always solve incompatibility. Mostly false — adapters exist for some combos (spacers, HG->XDR on certain hubs), but Micro Spline adapters are not a safe, standard solution.
Freehub standard is a wheel issue only. Partly false — some cassette designs (road vs MTB) dictate which freehub you need.
When to Choose/Use
If your cassette is Shimano 12‑speed MTB (10‑51T), choose a Micro Spline freehub or a wheel with Micro Spline hub.
If you run SRAM 12‑speed road (with 10T), you need an XDR driver or a wheel listed as XDR‑compatible.
If you have an older 8–11 speed cassette and want a simple swap, an HG freehub is your match.
If your hub has a removable body, swapping the body is usually cheaper than buying a new wheel. If it’s not removable, you’ll need a new hub or wheel.
Sources
Shimano Micro Spline tech (2020) — Micro Spline rationale and 10T compatibility.
SRAM XDR tech overview (2020) — XDR driver purpose and 12‑speed road compatibility.
Park Tool: Cassette removal & installation (2023) — practical lockring torque and installation guidance.
Key Takeaways
HG, XDR, and Micro Spline are mechanically incompatible splined freehub standards.
Micro Spline and XDR enable 10T smallest‑cog cassettes; HG generally does not.
Many hubs accept replaceable freehub bodies — swapping is cheaper than replacing a wheel.
Always check hub manufacturer specs or consult a shop before attempting a swap.
FAQs
Can I swap a freehub body to fit a different cassette?
Often yes. Many hubs use removable freehub bodies that can be swapped for HG, XDR or Micro Spline if the manufacturer offers those bodies and the correct endcaps. Check your hub spec and use proper tools or a shop tech.
Can I mount an HG cassette on a Micro Spline hub?
No. Micro Spline uses a different spline geometry and is not compatible with HG cassettes. Forcing a cassette risks damage—replace the freehub body or use a compatible cassette.
Related Blogs
Cassette to Freehub Compatibility Explained | Competitive Cyclist
Bike Compatibility Standards (BB, Freehub, Axles, Rotors, Tires) | Competitive Cyclist
Bike Drivetrain: 1x vs 2x, Chainline, Shifting & Wear | Competitive Cyclist
Bike Chain Compatibility Explained | Competitive Cyclist
How to Choose the Right Cassette Range (Road/Gravel/MTB) | Competitive Cyclist
How to Replace a Bike Cassette & Lockring (Tool + Chain Whip) | Competitive Cyclist