Atelier 700Open the shop

At the bench · At the bench

Setting Up a Rear Derailleur on the Bench at Home

The bench · September 1, 2026 · 6 min read

I sweep the floor here and I index gears slowly, because slowly is the only speed that works.

A rear derailleur is not a mysterious object. It is a parallelogram on a spring that a cable pulls sideways, and every setup problem is one of four things: a bent hanger, a wrong limit, a wrong cable tension, or a part that was never going to work with the drivetrain in the first place. Here is how we do it at the bench, in the order we do it, and which derailleurs the shop currently lists.

Before you touch a screw

Two things decide whether the job is a half-hour or a wasted afternoon. The first is the hanger. If it is bent inward, no amount of barrel-adjuster fiddling will make the shifts land, and you will spend the evening chasing a ghost. Sight down the cage from behind the bike: the two pulleys and the cog above them should sit in one plane. If they do not, that is a hanger alignment job before anything else.

The second is arithmetic you do before you buy. A derailleur declares how many rear speeds it expects, what kind of shifter signal it wants, and the largest cog it can wrap. Those three numbers are the whole compatibility conversation for this zone. Every fact we publish is read off a manufacturer or standards sheet and cited; a fact one publisher states is derived, and a fact two independent publishers agree on is verified. No bike in our fleet is fully verified yet. For derailleur speeds and actuation that is usually fine, because a mismatch there is a shifting problem, not a safety one.

Rear speeds12 speeds
Shift actuationMechanical (cable)
Chain standard12-speed HG+ / Eagle (5.25 mm)
Rear axle spacingThru-axle, 142 × 12 mm

Canyon Grail CF SL 7 (2025)

The bench procedure

Hang, limit, index, check

  1. Hang it square and torque it Thread the mounting bolt by hand first so you cannot cross the hanger threads. Make sure the b-tension tab sits behind the hanger stop, not on top of it, then bring the bolt up to the torque printed on the derailleur body. Leave the cable off for now.
  2. Set the b-gap Put the chain on the largest cog by hand, with the cable still disconnected, and turn the b-tension screw until the upper pulley sits close to the cog without touching or chattering. Too tight and the shifts grind; too far and the upper cogs shift lazily. Check it again in the smallest cog.
  3. Set the low limit, then the high limit Still with no cable, push the cage inboard by hand toward the spokes and adjust the inner limit screw so the upper pulley lines up under the largest cog and goes no further. Let it spring out and set the outer limit screw so the pulley lines up under the smallest cog. These two screws are the guardrails: nothing else stops the chain from going into the spokes or off the outside.
  4. Run the cable and take up slack Wind the barrel adjuster almost all the way in, then back it out a couple of turns so you have room both ways. With the shifter in its smallest-cog position, pull the cable snug with pliers, seat it in the groove and clamp it under the pinch bolt. Work the shifter through the range a dozen times to settle the housing, then re-clamp if the cable has crept.
  5. Index in the stand Pedal by hand and shift up one cog. If it hesitates going to the larger cog, add tension by turning the barrel adjuster counter-clockwise, a quarter turn at a time. If it overshoots or rattles, take tension away. Work the middle of the cassette first; the ends are governed by the limit screws, not by tension.
  6. Check the clutch and the chain length If the derailleur has a clutch, switch it on and feel the cage: it should swing out with resistance and return without flopping. Then check chain length in the largest cog at the front and rear — the cage should still have travel left and must not stretch straight. A chain that is too short will destroy a derailleur on the first rough climb.
  7. Ride it, then re-index New housing settles. After the first ride, put the bike back in the stand and expect to need a small barrel-adjuster correction. That is normal, not a failure of the setup.

The limit screws are guardrails. Nothing else keeps the chain out of the spokes.

What the shop lists for this zone

Three rear derailleurs are on our pages right now, and they read very differently against a bike on file. We compute a verdict from the bike's facts against the part's requirements; we do not guess, and an unknown is never a quiet yes.

BrandmicroSHIFT
Manufacturer part numberRD-M6195M
Requires — Rear speeds9 speeds
Requires — Shift actuationMechanical (cable)
Provides — Rear derailleur max cog46 t
Provides — Rear derailleur total capacity41 t

microSHIFT ADVENT medium-cage clutch rear derailleur, 9-speed

BrandSRAM
Manufacturer part numberRD-GX-1-B2
Requires — Rear speeds12 speeds
Requires — Shift actuationMechanical (cable)
Provides — Rear derailleur max cog52 t

SRAM GX Eagle rear derailleur, 12-speed

BrandSRAM
Manufacturer part numberRD-RIV-E-D1
Requires — Rear speeds12 speeds
Requires — Shift actuationSRAM AXS (eTap)
Provides — Rear derailleur max cog36 t

SRAM Rival eTap AXS rear derailleur, 12-speed

Rear derailleur — Canyon Grail CF SL 7 (2025)

My shifting is fine in the middle of the cassette but bad at both ends. What is wrong?
That pattern usually means cable tension is close to right and the limit screws are off, or the hanger is bent. Re-check the two limits with the cable disconnected, and sight the cage from behind for alignment.
Do I need a clutch derailleur for gravel?
You do not need one, but a clutch keeps the chain quieter and less likely to drop on rough ground. If your derailleur has one, switch it off before removing the wheel and back on before you ride.
Can I mix a derailleur with a different number of rear speeds if I only adjust it carefully?
No. Cable pull per shift and cog spacing are set by the drivetrain generation. If the speed counts do not match, the shifts will never index cleanly, and we will not sell a part into that mismatch.
Why does a verdict sometimes say unknown instead of yes?
Because a measurement is missing or only stated once. For safety-critical dimensions we wait until two independent sources agree. Unknown is an answer, not a stalling tactic, and it is never a quiet yes.

What to remember

  • Check the hanger first; a bent hanger defeats every other adjustment.
  • Order matters: hang, b-gap, limits with the cable off, then tension, then index.
  • Speed count and shift actuation decide compatibility before the largest cog does.
  • Re-index after the first ride; new housing always settles.
  • If a fit reads unknown on our pages, we do not have the facts yet and will not pretend otherwise.

None of the derailleur pages above carry a live offer today, so there is nothing to add to a basket from this article in 2026. What you can do is read the zone page, see which verdicts are derived and which are still open, and bring the bike in if a measurement you need is not on file. We would rather tell you we do not know yet than hand you a part that ends up in your spokes.

More in the Journal

  • What We Still Don't Know About the Grail CF SL 7

    The Canyon Grail CF SL 7 (2025) sits in our fleet with one source behind each fact and no second publisher agreeing yet. Here is what that means, which answers still stand, which ones wait, and what would change them.

  • SRAM DUB bottom brackets, sorted by shell

    Five SRAM DUB bottom brackets sit in the drawer. They all hand the crank the same spindle interface; what separates them is the frame shell they need. Here is each one by its numbers, plus the one projected verdict we have on file against a bike in the fleet.

  • The Cassette Shelf, Counted Cog by Cog

    Five cassettes are on file in the archive: one nine-speed microSHIFT, one twelve-speed Shimano, and three SRAM eleven-speed options. This guide lays out the three numbers that separate them — freehub body, rear speeds, and the smallest rear derailleur capacity they demand — and says plainly which bike in the fleet they do and do not fit.

  • Why your 11-speed chain fits — and the 12-speed one does not

    Chain compatibility comes down to one standard most boxes print as a speed count: the chain width. Here it is for the two KMC chains people ask about most, and what it means on an 11-speed and on a 12-speed bike from the fleet.

  • The Giant Escape 3, As Far As Our Paper Goes

    A plain accounting of the Giant Escape 3 (2024): the measurements we have on file, the ones we do not, the three regions worth reading before you buy, and four listed parts with their projected verdicts.

  • Rear Wheel of the Giant Fathom 29 2: What Bolts On

    A region guide to the rear wheel of the Giant Fathom 29 2 (2022): the cited frame and wheel facts we hold, the two Maxxis parts projected to fit, why each verdict lands where it does, and the measurements that are still missing from the file.

  • The Glory Advanced Is on File, Not Yet Verified

    Every fact we hold on the Giant Glory Advanced (2025) comes from a single cited source. That is enough to answer some questions and not enough to answer others. Here is exactly which is which, and what would move a line from unknown to answered.

  • Swapping a Cassette at Home, Without Guesswork

    A bench procedure for removing and installing a rear cassette, the spec rows that decide which cassette you can even buy, and the three cassette pages the shop lists — including why all three are projected not to fit the Canyon Grail CF SL 7 (2025).

  • The e12 chain and the Grail: a clean match on the drivetrain

    The KMC e12 e-bike chain, 12-speed fits the Canyon Grail CF SL 7 (2025). The chain standard on the bike's sheet matches the chain standard the part requires. Here is the reasoning, the rows behind it, and what happens when you bring an older chain to the same drivetrain.

  • The KMC X10, and the one thing it asks of your bike

    The KMC X10 chain, 10-speed has a single requirement: a 10-speed drivetrain. We read the spec rows, then check it against the two bikes on file with the same chain standard — the Giant Fathom 29 2 (2022) and the Kona Sutra (2025). Both come back as fits, on derived facts.

  • The X9 and the Roam: one chain, one answer

    The KMC X9 chain, 9-speed fits the Giant Roam 2 Disc (2021). The chain standard on the bike matches the chain standard the part asks for, and both facts are on file. Here is the reasoning, the spec rows behind it, and the chain that does not fit.

  • Rotor size is a safety question, not a taste

    A bigger rotor brakes harder. It also loads the fork mount beyond what it was tested for when it exceeds the fork maximum. Here is why a rotor reads "unknown" on a single-sourced bike, "does not fit" when the interface is wrong, and "unknown — safety-critical" when the maximum is not on file.

  • The 1.85 mm spacer: the cassette that confuses everyone

    An 8/9/10-speed cassette on an 11-speed road freehub: why there is a gap, why a 1.85 mm ring fills it, how the resolver treats that ring — and why the page can still say "unknown" after the freehub question is settled.

  • DUB: One Spindle, Four Shells

    SRAM DUB is a crank spindle standard measured at 28.99 mm. Here is what that number does mechanically, which bottom brackets in our archive carry it, and why the shell in your frame — not the spindle — decides what you can buy.

  • What "unknown" means in this shop

    A bike we have not verified stays on the floor with a sign on it, not in the back room. Here is what that sign says, with the Brompton C Line as the live example, and why we would rather lose the sale than guess.

The shop · Atelier 700