LTWOO ERX Rear Derailleur (RD-ER1203-OP)

Rear Derailleur

Specifications

Manufacturer: LTWOO
Name: ERX Rear Derailleur (RD-ER1203-OP)
Series: ERX
MPN: RD-ER1203-OP
Rear Speeds: 12
Drivetrain Brand: Other
Shifting Type: Wireless
Electronic Shifting Family: Ltwoo Electronic
Max Cog (T): 36^[1]
Mount Standard: Standard Hanger
Weight (g): 295^[1]
Sources: [1] ltwoo.com, checked 10 Aug 2026: Max Cog (T), Weight (g)

Compatibility

LTWOO ERX Rear Derailleur (RD-ER1203-OP) is a LTWOO rear derailleur. It is a 12-speed component. It uses Wireless shifting. Everything listed below was matched on a specification we hold for both parts: the interface each pairing actually depends on, such as freehub body, speed count, actuation or mounting standard. Where we could not verify that interface, the part is left out rather than assumed to fit.

Chains for this derailleur20

Shares a standard

SRAM

Apex Chain

Both are 12-speed

Shares a standard

Shimano

CN-M6100 HYPERGLIDE+ CHAIN 12s

Both are 12-speed

Shares a standard

Shimano

CN-M7100 HYPERGLIDE+ CHAIN 12s

Both are 12-speed

Shares a standard

Shimano

CN-M8100 HYPERGLIDE+ CHAIN 12s

Both are 12-speed

Shares a standard

Shimano

CN-M9100 HYPERGLIDE+ CHAIN 12s

Both are 12-speed

Shares a standard

KMC

DLC 12

Both are 12-speed

Shares a standard

KMC

e12

Both are 12-speed

Shares a standard

SRAM

Eagle 70 Transmission Flattop Chain

Both are 12-speed

Shares a standard

SRAM

Eagle S100 Chain

Both are 12-speed

Shares a standard

SRAM

Eagle S200 Chain

Both are 12-speed

Shares a standard

SRAM

Eagle S500 Chain

Both are 12-speed

Shares a standard

SRAM

Force Chain (CN-FRC-D1)

Both are 12-speed

Shares a standard

SRAM

Force Chain (CN-FRC-E1)

Both are 12-speed

Shares a standard

SRAM

GX Eagle Chain

Both are 12-speed

Shares a standard

SRAM

GX Eagle Transmission Flattop Chain

Both are 12-speed

Shares a standard

FSA

K-FORCE LIGHT MTB 12 SPEED CHAIN

Both are 12-speed

Shares a standard

SRAM

NX Eagle Chain

Both are 12-speed

Shares a standard

SRAM

RED Chain

Both are 12-speed

Shares a standard

SRAM

Rival Chain (CN-RIV-D1)

Both are 12-speed

Shares a standard

SRAM

Rival Chain (CN-RIV-E1)

Both are 12-speed

Cassettes for this derailleur1

Shares a standard

FSA

K-FORCE WE12S

Both are FSA drivetrain parts
The cassette's 32T largest cog is within the derailleur's 36T maximum

Shifters that drive this derailleur5

Recommended

LTWOO

ERX Shifter (ST-ER1202-2L-C)

Both use wireless actuation
Both are LTWOO drivetrain parts

Recommended

LTWOO

ERX Shifter (ST-ER1202-R-C)

Both use wireless actuation
Both are LTWOO drivetrain parts

Mechanically compatible

LTWOO

ER7 Shifter (ST-ER1002-2L)

Both use wireless actuation
Both are LTWOO drivetrain parts

Mechanically compatible

LTWOO

ER7 Shifter (ST-ER1002-R)

Both use wireless actuation
Both are LTWOO drivetrain parts

Mechanically compatible

LTWOO

Shift Switch (SW-ET1203)

Both use wireless actuation
Both are LTWOO drivetrain parts

Frequently Asked Questions

What fits LTWOO ERX Rear Derailleur (RD-ER1203-OP)?

On this page we list chains for this derailleur, cassettes for this derailleur, shifters that drive this derailleur. Each listing was matched on a specification we hold for both parts; anything we could not verify is omitted rather than assumed to fit.

Can I use a higher or lower speed chain with LTWOO ERX Rear Derailleur (RD-ER1203-OP)?

No. LTWOO ERX Rear Derailleur (RD-ER1203-OP) is a 12-speed component and needs a 12-speed chain. Chains for different speed counts have different external widths and inner-plate profiles, which causes poor shifting or interference with the neighbouring sprockets.