HG, XDR or Micro Spline: order the freehub after the cassette

Read the cassette requirement, not the brand guess

HG, XDR and Micro Spline name different interfaces. Even “HG” needs the correct body version and length. Shimano’s freehub guide explains why its twelve-speed road and mountain offerings do not all use the same interface. Save the cassette code and the relevant compatibility row with your order.

For a concrete contrast, Shimano lists its CS-R7101-12 11–34T as compatible with a road 11-speed FREEHUB body, while the CS-M8100-12 10–51T uses Micro Spline. Both have twelve sprockets. If a wheel quote says only “Shimano 12-speed,” it has not resolved which cassette can mount. Send the exact code before approving the body; passing this mounting check still does not approve the rest of the drivetrain.

A spacer rule has a direction

SRAM specifies a 1.85 mm spacer for an XD cassette on an XDR body. That is not permission to fit an XDR cassette to an XD body or to add that spacer to every cassette. Follow the exact cassette installation instructions, including the required hardware and tightening method.

Make the replacement body a real part number

For a GRARO build, list wheel/hub model, cassette model, freehub part number and any specified spacer. A replacement body is usually hub-specific; a loose “XDR body” found online is not automatically useful. Ask whether the conversion also needs an end cap, seal or other hardware. SRAM’s conversion guidance directs you to the hub manufacturer for a kit for the existing rear hub.

If you expect to change drivetrain later, price the supported conversion before buying the wheels. If no replacement can be identified, record that limitation. It may be cheaper to order the correct wheel configuration now than to discover that the future upgrade requires another wheelset.

For the next checks, use the Shimano/SRAM compatibility-chain guide and the cassette range and gear-jump guide.