AI quick summary
- Five freehub standards: Shimano HG (the universal default for 8–11 speed), SRAM XD (for 10T-start 12-speed cassettes), Shimano MicroSpline (for 10T-start Shimano 12-speed), Campagnolo (Campy 9–12 speed), and Campagnolo N3W (for 10T-start Campy cassettes)
- The standard matters because cassettes are NOT cross-compatible: a Shimano cassette won't fit an XD freehub, and vice versa. Check your freehub before buying a cassette or new wheels
- The 10T-start revolution: XD, MicroSpline, and N3W all exist to allow a 10-tooth smallest sprocket (vs the 11T limit of HG). This gives wider gear range without making the cassette bigger — the 10T start is why 1x12 drivetrains can offer 510% range
- Many modern wheels offer interchangeable freehub bodies — you can swap from HG to XD or MicroSpline by removing 3 bolts and swapping the body. Check if your wheels are convertible before buying new ones
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The five standards
Freehub standards by brand and speed. The freehub determines which cassettes fit your wheel.
| Standard | Brand | Speeds | 10T start? | Found on |
|---|---|---|---|---|
| HG (Hyperglide) | Shimano | 8–11 speed | No (11T smallest) | Most road/MTB wheels, universal default |
| XD | SRAM | 11–12 speed | Yes (10T) | SRAM Eagle, AXS road (XDR variant) |
| MicroSpline | Shimano | 12 speed | Yes (10T) | Shimano 12-speed MTB (XTR/XT/SLX/Deore), GRX 12s |
| Campagnolo | Campagnolo | 9–12 speed | No (11T) | Campagnolo groupsets (pre-N3W) |
| N3W | Campagnolo | 12 speed (Super Record Wireless) | Yes (10T) | Campagnolo Super Record Wireless only |
/ 02
Why so many standards?
The original problem: the HG freehub (Shimano's design, adopted industry-wide) uses splines designed for an 11-tooth smallest sprocket. To fit a 10T cog — which gives wider range without a bigger cassette — you need finer, deeper splines. Each brand created its own solution: SRAM's XD (threaded, 10T-capable), Shimano's MicroSpline (finer splines, 10T-capable), and Campagnolo's N3W (a shorter version of the Campy body, 10T-capable).
The result: five standards, minimal cross-compatibility. A Shimano 11-speed cassette fits HG; a Shimano 12-speed MTB cassette fits MicroSpline; a SRAM 12-speed cassette fits XD. They don't interchange. Before buying a cassette or new wheels, verify which freehub standard your current wheels use.
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How to check yours
Visual check: remove the rear wheel and look at the freehub body (the splined cylinder the cassette slides onto). If the splines are relatively wide and evenly spaced, it's HG. If the splines are finer and more numerous (looks like a fine-tooth comb), it's MicroSpline. If the cassette threads onto the body (rather than sliding on with a lockring), it's XD. If it looks different from all of the above and you have Campagnolo, it's Campy or N3W.
Check the wheel manufacturer's spec: most wheel brands list the freehub standard in the product page or manual. Many modern wheels (DT Swiss, Zipp, Cadex, Hunt) offer interchangeable freehub bodies — you can buy an XD or MicroSpline body ($50–100) and swap it onto an HG wheel, converting it. This is much cheaper than buying new wheels if you switch groupsets.
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Buying advice
Match the freehub to your groupset. If you ride Shimano 11-speed, HG is universal — any HG wheel works. If you ride SRAM 12-speed (Eagle, AXS), you need XD (or XDR for road). If you ride Shimano 12-speed MTB or GRX 12s, you need MicroSpline. If you ride Campagnolo, you need Campy (or N3W for Super Record Wireless).
Future-proofing: if buying new wheels, choose a brand with interchangeable freehub bodies (DT Swiss 350/240, Zipp, Cadex, Hunt). This lets you switch standards if you change groupsets later, without buying new wheels. The $50–100 freehub swap is a small price for flexibility.
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