Setting chain length on a 12-speed bike

Signs the chain is the wrong length

Chain is very tight on the largest sprocket, or the derailleur hits the frame

Too short. Shimano warns a short chain overloads and damages the drivetrain. SRAM's Transmission troubleshooting gives a short chain as the cause of a chain that is too tight on the largest cog or a derailleur that hits the frame.

Chain bounces or slaps in the small cogs

Too long. On SRAM Transmission, SRAM also lists cage damper torque that is too low. Check the length first.

Chain skips under load

SRAM lists a chain that is too long among the causes, along with a dirty or worn chain and cassette and a chain gap that is too large.

New chain fitted and shifting is now off

Check length against the method for your derailleur. On SRAM Eagle Transmission, a new chain means redoing the full derailleur installation.

Which method is yours

The biggest difference for full-suspension bikes: Shimano sizes the chain with the suspension fully extended, then checks it is not too short at full chainstay extension. SRAM GX Eagle sizes it with the rear shock fully compressed (shock deflated or removed). Use the method for your derailleur, not the other brand's.

Shimano 12-speed: Deore M6100 and 105 R7100

Both start the same way: wrap the chain over the largest chainring and the largest sprocket without threading it through the derailleur, and bring the two ends together at the back of the cassette. Shimano calls this the zero point. The number of links you then add depends on the derailleur.

• Deore, full suspension: size with the suspension fully extended. Then shift to the largest chainring and largest sprocket and check the chain is not too short at the point where the chainstay is longest in the travel.
• 105 with a UDH hanger: check there is no chain slack in any gear. If there is, Shimano says to use the B-screw. Also use the B-screw if the derailleur is too close to the chainstay. Set the B-screw gap afterwards as on the derailleur page.
• Route the chain through the cage on the derailleur-body side of the chain guide pin or plate. Shimano warns wrong routing can damage the chain or derailleur.
• The CN-M6100 chain is joined with a QUICK-LINK, not a connecting pin. Shimano says CS-M6100 cassettes must be used with CN-M9100, CN-M8100, CN-M7100 or CN-M6100 chains. RD-R7100 takes an HG 12-speed chain.

Shimano CUES (LINKGLIDE)

CUES has two derailleur families with different zero points, so check your model number.

As with Deore, size a full-suspension bike with the suspension fully extended, then check in the largest chainring and largest sprocket that the chain is not too short at full chainstay extension. Route the chain on the derailleur-body side of the cage's chain guide plate.

CUES LINKGLIDE cassettes (CS-LG700, CS-LG400, CS-LG300, CS-RS400) must be used with HG-X 11-speed chains or CN-LG500; Shimano says other chains do not match their dimensions. CN-LG500 has a marked side that must face out.

SRAM GX Eagle

Before you start: SRAM warns that a chain sized or joined wrongly can fail and cause a crash. Keep fingers clear of the cage when you lock it open; it is spring loaded.

1. Full suspension: size the chain with the rear shock fully compressed. Let the air out of the shock or remove it. Frames with an upper idler pulley need a lower idler too.

2. Round X-SYNC or X-SYNC 2 chainring: wrap the chain around the chainring and the largest cog, without going through the derailleur.

3. Where the chain starts to overlap, add one inner and one outer link on full-suspension and idler bikes, or two inner and two outer links on a hardtail.

4. Break the chain so an inner link is left exposed, and throw away the outer link and the extra chain.

5. Oval X-SYNC 2 chainring: set the crank at the 1 o'clock position, wrap the chain the same way, and add the number of links from the chart in SRAM's manual.

   From the SRAM 1x MTB Mechanical Derailleurs User Manual, Chain Sizing, pp. 25–28

Fit the chain on the smallest cog, lock the cage forward with the Cage Lock button and join it with the PowerLock, arrow pointing in the direction of chain travel. Release the cage, turn the crank until the PowerLock is above the chainstay, hold the rear brake and push the crank down firmly until it clicks. Then set the chain gap: see GX Eagle chain gap.

SRAM Eagle Transmission

For frames in SRAM's database, Transmission chain length is not measured on the bike. SRAM gives the link count, along with the Setup Key position and Setup Cog, for each listed frame.

1. Look up the chain length, Setup Key position (A or B) and Setup Cog (21T or 24T) for your frame in SRAM's Full Mount Chain Length Guide or the SRAM AXS app. SRAM says the online guide is the most accurate source and that the printed table may differ from it.

2. An aftermarket T-Type chain has 126 links. Count down from 126 to the number you need and break the chain at an inner link with an approved chain tool.

3. Some bikes need two chains joined with a second PowerLock. Place the two PowerLocks as far apart as possible.

4. Frame not in SRAM's database: use Setup Key A and the 21T Setup Cog, and tighten the derailleur with the bike at sag. Frames with idler pulleys: wrap the chain over the large chainring, the idler and the largest cog with the shock fully compressed, and add one inner and one outer link where it overlaps.

   From the SRAM Eagle Transmission User Manual, Prepare

The chain is then fitted on the Setup Cog and the derailleur is tightened with the cage pulled back. SRAM says to repeat the full installation if you change the chain, the chainring size, the chainstay length or the lower idler position. Steps: prepare, install, replace the chain.

Chains and connecting links

• Shimano QUICK-LINKs and SRAM PowerLocks are one-time use. Fit a new one whenever you fit a new chain or open the link.
• Shimano says a QUICK-LINK needs a Shimano tool to remove it. SRAM PowerLocks are opened with chain link pliers.
• Replace SRAM Eagle and T-Type chains at 0.8% elongation, measured with a SRAM chain wear tool.

Cut and join the chain

1. Seat the chain correctly in the cutter and push the pin fully out. Shimano says a badly seated chain can damage the cutter's positioning plate.

2. Never cut a Shimano chain at a link that was joined by a QUICK-LINK or at a reinforced connecting pin.

3. Shimano QUICK-LINK: fit the two halves into the inner links from each side, arrow pointing in the direction of crank rotation, and pull them together until both sides are fully seated. Check both sides.

4. Shimano connecting pin (CN-LG500): push it in from the same side you used the cutter, break off the extra part, and check it sits slightly proud as Shimano's manual shows.

5. SRAM PowerLock: arrow in the direction of chain travel. With the link above the chainstay, hold the rear brake and push the crank down firmly until it clicks, then check it moves freely.

6. Shift through every gear, check the chain does not go tight on the largest sprocket, then check derailleur adjustment on the derailleur page.

Tiagra 4700 (10-speed) uses a different rule: with a largest sprocket of 27T or less on a double, size the chain on the largest chainring and smallest sprocket so the line through both pulleys is at 90° or more to the ground; with 28T or more, find the shortest length over the largest chainring and largest sprocket and add 2 links. Details are on the Tiagra 4700 page.

Related: Adjust a rear derailleur, Shimano Deore M6100, Shimano 105 R7100, Shimano CUES, SRAM GX Eagle, SRAM Eagle Transmission