Last Updated on March 2, 2026 by Vinson Lozano
If you’ve ever tried to upgrade your bike’s gears or swap wheels and found that things don’t fit together, you’ve bumped into the world of hub bodies. Don’t worry—this guide will make it clear and simple. Whether you’re a beginner riding around the neighborhood or an advanced cyclist tinkering with gear ratios, you’ll learn how different hub body standards work, why they exist, and how to choose the right one for your bike.
Think of a hub body like a keyhole on your rear wheel. Your cassette (the stack of gears) is the key that fits into that keyhole. Different brands designed different keyholes, and not every key fits every lock. This guide explains those “locks” and “keys,” how to identify yours, and what your options are when you want to change or upgrade.
You’ll find:
- Clear explanations of the major hub body types: Shimano HG, Shimano Micro Spline, SRAM XD, SRAM XDR, and Campagnolo (classic and N3W)
- Compatibility tips that prevent expensive mistakes
- Beginner-friendly definitions with details advanced riders will appreciate
- Advice on upgrades, materials, and common myths
- A quick decision guide and FAQ at the end
First Things First: What Is a Hub Body?
- Hub: The center part of your wheel where the spokes attach. The rear hub sits at the center of your back wheel.
- Freehub body (often just “hub body”): The part of the rear hub that the cassette slides onto. It also houses the mechanism that lets you coast while the wheel keeps spinning.
- Cassette: The stack of gears on your rear wheel.
- Freewheel: An older style where the gears and the ratchet mechanism are all one piece that threads onto the hub. Most modern bikes use freehub+cassette systems instead.
Your rear hub has a specific shape and size where the cassette mounts. That shape and size is the hub body standard. If you try to use a cassette that doesn’t match the hub body, it won’t fit.
Why So Many Standards?
- Gear range: Smaller smallest cogs (like 10 teeth) and bigger biggest cogs (like 50+ teeth) need different shapes and strengths.
- Speed count: 8, 9, 10, 11, 12, or even 13 speeds—more cogs often mean new designs.
- Brand ecosystems: Different companies create their own systems for performance, patents, or design goals.
- Road vs. mountain: Different use cases (smooth roads vs. rugged trails) lead to unique requirements.
The Big Players: Hub Body Standards You’ll See Most
1) Shimano HG (HyperGlide)
The Shimano/SRAM “HG” pattern is the most common and oldest modern standard. It’s used on tons of wheels and cassettes across road, gravel, and mountain bikes.
- What it looks like: A splined (ridged) cylinder with one wider groove that keys the cassette orientation.
- Smallest cog: Typically 11 teeth (sometimes 12). HG does not support a 10-tooth cog from Shimano directly (some third-party exceptions exist).
- Common speeds: 8, 9, 10, 11, and many 12-speed cassettes (note: compatibility varies with brand and chain systems).
Important detail: There are two “lengths” of HG freehub bodies:
- HG (8/9/10/11-speed MTB width): Fits most 8, 9, 10-speed, and 11-speed mountain cassettes of the HG type.
- HG 11-speed Road: Slightly longer (about 1.8 mm longer) to fit 11-speed road cassettes. Many 11-speed road cassettes need this longer freehub.
Practical notes:
- Installing 10-speed (or 9-speed) road cassettes on an 11-speed road freehub usually requires a spacer (often around 1.8–1.85 mm; check your cassette instructions).
- Many 11-speed mountain cassettes using HG are designed to fit the older, shorter (8/9/10) HG body by “dishing” the biggest cog over the hub flange.
- Shimano’s 12-speed road cassettes (like Dura-Ace/Ultegra/105 12-speed) are designed to fit the 11-speed road HG freehub.
- Some third-party brands (like SunRace) offer 12-speed HG cassettes for MTB or gravel. They can fit HG bodies but may have specific chain compatibility requirements. Check the manufacturer’s guidance.
Use HG if:
- You’re running Shimano or SRAM 8–11 speed road or MTB and don’t need a 10-tooth smallest cog.
- You’re on Shimano 12-speed road.
- You want the most widely compatible, easy-to-find ecosystem.
2) Shimano Micro Spline
Shimano created Micro Spline to support 12-speed mountain drivetrains with a 10-tooth smallest cog and improved engagement for wide-range cassettes.
- What it looks like: Many fine splines (more than HG). It’s visually tighter and more “toothy” than HG.
- Smallest cog: 10 teeth.
- Common speeds: 12-speed (primarily MTB and some gravel/Adventure).
- Focus: Shimano 12-speed mountain groups (e.g., Deore, SLX, XT, XTR 12-speed) and increasingly gravel 1x setups that use 10-45 or 10-51 cassettes.
Practical notes:
- Micro Spline is not just “new HG.” It’s a different shape.
- Most Shimano 12-speed MTB cassettes require Micro Spline (not HG).
- Not as universal as HG yet, but many hub makers now offer Micro Spline driver bodies you can swap onto compatible hubs (DT Swiss, Hope, Industry Nine, etc.).
- Shimano 12-speed road cassettes are designed for HG 11-speed road, not Micro Spline.
Use Micro Spline if:
- You want Shimano’s 12-speed MTB or gravel cassettes with a 10-tooth smallest cog.
- Your wheel/hub can take a Micro Spline driver body (or already has one).
3) SRAM XD
SRAM XD was created to support a 10-tooth smallest cog on mountain bikes. It’s used for SRAM 11- and 12-speed MTB cassettes that start at 10 teeth.
- What it looks like: A conical/stepped interface that the cassette slides over; the smallest cog is often integrated with the cassette and clamps directly onto the driver.
- Smallest cog: 10 teeth.
- Common speeds: 11- and 12-speed MTB.
- Focus: SRAM mountain cassettes with 10T (e.g., X01, GX Eagle, NX Eagle—note: NX 11/12-speed HG cassettes exist too; check your exact model).
Practical notes:
- XD uses a different lockup method compared to HG; the cassette tightens with an integrated securing method rather than a separate external lockring.
- Many hub brands offer swappable XD drivers.
- Some third-party cassettes (e*thirteen, Garbaruk, etc.) also make XD-compatible 11/12-speed cassettes.
Use XD if:
- You run SRAM 11- or 12-speed MTB with 10T smallest cog.
- You want wide-range MTB gearing in the SRAM ecosystem.
4) SRAM XDR
XDR is the “road” version of XD. It’s essentially an XD driver that is longer (by about 1.8 mm) to better match the spacing of road cassettes.
- What it looks like: Similar to XD but slightly longer.
- Smallest cog: 10 teeth.
- Common speeds: 11- and 12-speed road/gravel SRAM cassettes designed for XDR.
- Focus: SRAM road and gravel groups (e.g., Force/Rival/Red eTap AXS), typically 12-speed cassettes like 10-28, 10-30, 10-33, 10-36.
Compatibility trick:
- XDR is 1.8 mm longer than XD.
- You can run an XD cassette on an XDR driver by using a 1.8 mm spacer (many XDR drivers include this).
- You cannot run an XDR-only cassette on an XD driver (there’s not enough length).
Use XDR if:
- You run SRAM 12-speed road/gravel with 10T smallest cog.
- You want future-proofing in the SRAM road ecosystem.
5) Campagnolo (Classic) and Campagnolo N3W
Campagnolo has its own long-standing freehub pattern used on many of its road cassettes, and a newer standard called N3W for modern setups.
Classic Campagnolo freehub:
- What it looks like: A distinct spline pattern that is not HG, XD/XDR, or Micro Spline.
- Smallest cog: Typically 11 teeth (varies by cassette).
- Common speeds: 9–12-speed Campagnolo road cassettes.
- Use if: You run classic Campagnolo drivetrains and cassettes.
Campagnolo N3W (Next 3 Ways):
- Designed for modern 12- and 13-speed applications (e.g., Ekar 1×13 gravel).
- Shorter than the classic Campagnolo body, but backward compatible with an adapter sleeve.
- With a specific adapter, many older Campagnolo 9–12-speed cassettes can fit an N3W driver.
- N3W is primarily seen on Campagnolo-equipped wheels and hubs, and is increasingly supported by third-party hubs with swappable drivers.
Use N3W if:
- You want Campagnolo’s latest gravel/road drivetrains (e.g., Ekar 13-speed).
- You want flexibility: with the adapter, you can also run many older Campagnolo cassettes.
Less Common or Special Cases
- Fixed-gear/Track: These hubs don’t use a freehub body for a cassette. Instead, a single cog threads on, and a lockring secures it. Not compatible with HG/XD/XDR/Micro Spline/Campagnolo cassettes.
- Single-speed (freewheel): Older or budget bikes may use a threaded freewheel unit. These are not compatible with freehub cassettes. Some hubs accept single-speed “drivers,” but that’s a different system.
- Single-speed conversions: You can install a single-speed kit on an HG freehub using spacers and a single cog. Not the same as a fixed-gear because you still have a freewheel mechanism in the hub.
- Internal gear hubs (IGH): Hubs like Rohloff or Shimano Nexus/Alfine have their own systems and don’t use standard cassettes. These aren’t “freehub bodies” in the typical sense.
Quick Compatibility Cheat Sheet
- Shimano HG (short/MTB-width): Works with most 8/9/10-speed and many 11-speed MTB cassettes. Some 12-speed aftermarket cassettes fit HG, but check compatibility.
- HG 11-speed Road (longer): Needed for many 11-speed road cassettes; also used by Shimano’s 12-speed road cassettes. You can often install 9/10-speed road cassettes here with a spacer.
- Shimano Micro Spline: Required for Shimano 12-speed MTB (10T smallest cog). Increasingly used on gravel 1x when a 10T is desired.
- SRAM XD: Used for SRAM 11/12-speed MTB cassettes with a 10T smallest cog.
- SRAM XDR: Road/gravel version of XD; 1.8 mm longer. XD cassettes can fit XDR with a spacer; the reverse is not true.
- Campagnolo Classic: For older 9–12-speed Campagnolo cassettes.
- Campagnolo N3W: For modern Campagnolo cassettes (including 13-speed Ekar). With an adapter, can fit many classic Campagnolo cassettes.
Tip: A 10-tooth smallest cog almost always means you need Micro Spline (Shimano MTB) or XD/XDR (SRAM). Shimano road currently sticks with 11-tooth smallest cogs on HG.
How to Identify the Hub Body on Your Wheel
Beginner-friendly checks:
- Count the smallest cog teeth:
- 10T smallest = likely XD/XDR (SRAM) or Micro Spline (Shimano 12-speed MTB).
- 11T smallest (or larger) = often HG (or Campagnolo).
- Brand and groupset:
- Shimano 12-speed MTB (Deore, SLX, XT, XTR) = Micro Spline.
- SRAM 12-speed road (eTap AXS) = XDR.
- SRAM 12-speed MTB (GX/X01/XX1 with 10T) = XD.
- Shimano 12-speed road (Dura-Ace/Ultegra/105 12-speed) = HG (11-speed road length).
- Campagnolo modern gravel (Ekar 13) = N3W.
- Look at the driver shape:
- HG: Splines with one noticeably wider groove.
- Micro Spline: Many fine splines; “denser” look than HG.
- XD/XDR: Tapered/conical form; cassettes slide on and clamp; no big external lockring like HG.
- Campagnolo: Unique spline pattern—notably not the same as HG.
- Check your wheel/hub model online:
- Many hub brands list which drivers are available for your hub (DT Swiss, Hope, Industry Nine, Novatec, etc.). A quick search often reveals what you have and if you can swap drivers.
- If your hub supports it, swapping is often straightforward:
- Many modern hubs allow you to change the driver body by removing end caps and pulling off the driver. This can switch your wheel between HG, XD/XDR, and Micro Spline, depending on available parts.
Road vs. Mountain Differences to Know
- 11-speed road HG freehubs are a bit longer than the old 8/9/10-speed HG body. That’s why spacers are sometimes needed when fitting fewer-speed cassettes onto newer road wheels.
- 11-speed mountain HG cassettes were designed to fit the older, shorter HG body (clever spacing tricks), so you didn’t need a new freehub to run 11-speed MTB.
- 12-speed Shimano road stays on HG 11-speed road, while 12-speed Shimano MTB requires Micro Spline.
- SRAM splits 10T-supporting drivers between MTB (XD) and road (XDR), distinguished largely by length.
Materials: Steel vs. Aluminum Drivers
Hub bodies come in different materials with pros and cons:
- Aluminum: Light, common on mid- to high-end wheels. Can develop “bite marks” where steel cassette cogs dig into the splines over time. Many cassettes use carriers to reduce bite. Some hub bodies include anti-bite plates or hardened inserts.
- Steel: Heavier, more durable, resists bite marks better—popular for e-bikes and high-torque use.
- Titanium or hybrid: Rare and expensive, sometimes seen on boutique hubs.
If you ride an e-bike or produce a lot of torque, consider a steel freehub body for durability.
Engagement, Noise, and the Freehub Mechanism
The hub body standard determines cassette fit, but engagement and noise come from the hub’s internal mechanism (pawls, ratchets, springs):
- Pawl systems: Clicking sound when coasting; engagement angle depends on pawl count and ratchet teeth.
- Ratchet systems (e.g., DT Swiss Star Ratchet): Often smoother engagement and easy servicing.
Note: The hub body type (HG, XD, etc.) doesn’t dictate hub noise. That’s a function of the internal mechanism and lubrication.
Myths, Pitfalls, and Pro Tips
- “All 12-speed Shimano needs Micro Spline.” Not true: Shimano 12-speed road cassettes fit HG 11-speed road freehubs. Shimano 12-speed MTB typically needs Micro Spline.
- “SRAM equals XD/XDR only.” Not always. Some SRAM 11-speed road cassettes fit HG. SRAM 12-speed road (AXS) typically uses XDR.
- “Boost hubs need a different freehub body.” Not by default. Boost (148 mm) refers to hub width and axle spacing, not the freehub standard. The driver type (HG/XD/XDR/MS) is separate.
- “All 11-speed cassettes fit any HG hub.” No. Many 11-speed road cassettes require the longer HG 11-speed road freehub. 11-speed MTB often fits the shorter HG.
- “You can mix any 12-speed cassette with any 12-speed chain.” Be careful. 12-speed chains differ (Shimano 12-speed chains are narrower with special plate shapes). Match cassette and chain brand guidance to ensure shifting quality.
- Always check your wheel/hub manufacturer: Many allow swapping drivers. If your hub supports it, you can change from HG to XD/XDR or Micro Spline with a simple parts swap. Some OEM/budget wheels don’t offer swappable drivers.
Upgrade Scenarios: What You Need to Know
- I have an 11-speed Shimano road bike and want to go 12-speed Shimano road.
- Good news: Shimano 12-speed road cassettes fit HG 11-speed road freehubs. You likely don’t need a new wheel or driver (double-check your specific wheel and cassette).
- I have 11-speed Shimano MTB on HG and want 12-speed Shimano MTB with a 10T smallest cog.
- You’ll need a Micro Spline driver and a compatible cassette. Your hub may support swapping the driver. If not, you may need a new hub or wheel.
- I have SRAM 11-speed MTB and want 12-speed Eagle with a 10T smallest cog.
- You’ll need an XD driver and an Eagle cassette. Many hubs allow a driver swap.
- I’m building a gravel bike and want wide range with a 10T.
- SRAM: Use XDR for 12-speed road/gravel cassettes that start at 10T.
- Shimano: Use Micro Spline for 12-speed gravel 1x with 10T (often the same cassettes as MTB, like 10-45). For 2x 12-speed gravel with 11-34, you can stick with HG 11-speed road.
- Can I run an XD cassette on an XDR driver?
- Yes, with a 1.8 mm spacer. Many XDR drivers include this.
- Can I run an XDR cassette on an XD driver?
- No. The XDR cassette requires the longer driver.
- I only have HG but want a 10T small cog for road.
- Options are limited. Shimano road doesn’t use Micro Spline for 10T cogs. SRAM road uses XDR for 10T. If your hub supports a driver swap, convert to XDR. If not, consider a new hub or wheel.
- I’m on a budget and want 12-speed on HG.
- Some third-party brands offer 12-speed cassettes for HG, but shifting performance and chain compatibility can vary. Read reviews and manufacturer guidance carefully.
Swapping Drivers: How It Works
Many quality hubs and wheelsets allow you to swap the freehub body (driver) so you can change standards without buying a new wheel:
- DT Swiss (Star Ratchet/EXP): Offers HG, XD, XDR, and Micro Spline drivers. Usually a tool-free swap once the end cap is removed.
- Hope, Industry Nine, Chris King, Novatec, and others: Offer alternate drivers, though procedures and parts vary.
Before buying:
- Confirm your hub model and generation.
- Check driver availability (HG, XD, XDR, Micro Spline, Campagnolo) for your specific hub.
- Ensure axle end caps (and sometimes bearings) match the new driver if required.
Road, Gravel, MTB, and E-Bikes: Practical Tips
- Road:
- If you’re Shimano-based and not aiming for a 10T, HG 11-speed road freehubs are a safe, widely supported choice—even for Shimano 12-speed road.
- SRAM AXS road typically uses XDR; plan accordingly if mixing wheels between bikes.
- Gravel:
- Shimano 2x 12-speed gravel (e.g., GRX 12-speed 2x) often sticks to HG 11-speed road cassettes (11-34 or similar).
- Shimano 1x 12-speed gravel with very wide range (10-45 or 10-51) uses Micro Spline.
- SRAM wide-range gravel with a 10T uses XDR.
- MTB:
- Shimano 12-speed MTB: Micro Spline.
- SRAM 12-speed MTB (10-50/52): XD.
- E-Bikes:
- High torque can chew up softer aluminum HG bodies. Consider steel drivers for durability.
- Micro Spline and XD/XDR bodies are available in robust versions; choose according to your drivetrain and torque needs.
How to Avoid Costly Mistakes
- Always match cassette to driver type first (HG, Micro Spline, XD, XDR, Campagnolo).
- Then match cassette to chain and derailleur family (Shimano/SRAM/Campagnolo 12-speed systems are not universally cross-compatible).
- Verify hub compatibility for driver swaps using the hub maker’s documentation.
- Be mindful of spacer requirements when mounting older cassettes onto longer freehubs (e.g., 10-speed road cassette onto an 11-speed road HG body).
Decision Guide: Which Hub Body Should I Choose?
- If you’re staying with Shimano road (11 or 12-speed) and don’t need a 10T smallest cog:
- Choose HG 11-speed road.
- If you want Shimano 12-speed MTB or gravel 1x with 10T:
- Choose Micro Spline.
- If you’re on SRAM 12-speed road/gravel:
- Choose XDR.
- If you’re on SRAM 11/12-speed MTB with 10T:
- Choose XD.
- If you’re running classic Campagnolo:
- Use Campagnolo Classic.
- If you’re on modern Campagnolo (like Ekar 13-speed):
- Use Campagnolo N3W (with adapter for older Campagnolo cassettes if needed).
- If your hub supports driver swaps and you want flexibility:
- Consider a hub that offers HG, XD/XDR, and Micro Spline drivers so you can switch as your drivetrain changes.
Final Tips for Beginners (and a Refresher for Pros)
- Keep it simple: Think “lock and key.” Cassette = key, hub body = lock. Make sure they match.
- Look for 10T: If your smallest cog is 10 teeth, you likely need Micro Spline (Shimano MTB/gravel) or XD/XDR (SRAM).
- When in doubt, check your wheel/hub and cassette model numbers and look up the specs.
- Don’t forget spacers: Shorter cassettes (fewer speeds) on longer freehubs may need spacers.
- Get the right chain and derailleur to match your cassette’s brand and speed. Mixing can work in some cases but can also cause rough shifting.
In a Nutshell
- Shimano HG is the classic standard—still hugely important for road and many setups.
- Shimano Micro Spline is for 12-speed MTB/gravel with 10T.
- SRAM XD is for MTB with 10T; XDR is the road length version of XD.
- Campagnolo has classic and N3W; N3W adds modern flexibility and can often be used with an adapter for older cassettes.
- Many hubs let you swap drivers so you can adapt your wheels to new drivetrains.
- Always check compatibility before you buy upgrades.
With this knowledge, you’ll be ready to choose the right hub body, avoid costly mistakes, and set up your bike for smooth, reliable shifting—whether you’re cruising to school or racing a gravel epic.
Frequently Asked Questions
Q: Can I put a Shimano cassette on an XD driver?
- No. Shimano HG cassettes won’t fit XD drivers. You need the correct driver for your cassette type.
Q: What’s the difference between XD and XDR again?
- XDR is a longer version of XD for road/gravel spacing. XD cassettes can fit XDR with a 1.8 mm spacer; but XDR cassettes won’t fit on XD.
Q: I have an 11-speed road cassette and a wheel with an HG freehub. Why won’t it fit?
- If your wheel’s HG body is the shorter (8/9/10-speed) MTB-width HG, many 11-speed road cassettes won’t fit because they need the longer HG 11-speed road freehub.
Q: Do I need Micro Spline for Shimano 12-speed road?
- No. Shimano 12-speed road cassettes fit the HG 11-speed road freehub.
Q: I want a 10-tooth smallest cog with Shimano road.
- Shimano road currently doesn’t use a 10T smallest cog on HG. If you want 10T on road, SRAM XDR is the typical route. Shimano 10T options are mainly on 12-speed MTB/Gravel with Micro Spline.
Q: My hub is old. Can I swap drivers?
- It depends on the brand and model. Many modern hubs allow it, but some older or OEM hubs don’t. Check the manufacturer’s website or consult your local shop.
Q: What’s the easiest way to tell what driver I have?
- Remove the cassette and inspect the shape. Compare to pictures/descriptions:
- HG: Classic splines with one wider groove.
- Micro Spline: Many fine splines.
- XD/XDR: Tapered/conical look; cassette typically has an integrated securing method.
- Campagnolo: Unique spline pattern.
