Derailleurs

Shimano Ultegra Di2 RD-R8050 achterderailleur 11-voudig

The Shimano Ultegra Di2 RD-R8050 is a black electronic rear derailleur for 11 speeds. Di2 stands for electronic shifting.

What you get

Rear derailleur from Shimano
Ultegra Di2 RD-R8050, 11 speeds
Electronic, black

Why a new derailleur?

A derailleur takes a lot of punishment: knocks, mud, a crash or a stick in the spokes. A bent cage or a damaged parallelogram makes shifting vague, even after adjustment. Replacing it is then often better than continuing to adjust.

A derailleur has to match your number of sprockets and your shifter. An 11-speed derailleur works with an 11-speed shifter, and brand and type must agree. A Shimano road derailleur pulls differently from a Shimano MTB one, and SRAM and Shimano use different cable pull ratios.

Also look at cage length and capacity. A short cage (SS) suits ranges up to about 11-28 or 11-30. A medium cage (GS) takes cassettes up to about 11-34 or 11-36. A long cage goes with wide MTB cassettes. A derailleur that is too small cannot tension the chain well.

Many modern MTB derailleurs have a clutch: a brake that holds chain tension and reduces chain slap and chain drops. Electronic derailleurs shift at the push of a button and stay adjusted, but need a battery.

How the types compare

Cage length and control decide which cassette and shifter go with it.

Type	Largest sprocket	Suits	Watch for
Short cage (SS)	Usually up to 28 or 30 teeth	Racing and fast road	Little room for wide cassettes
Medium cage (GS)	Usually up to 34 or 36 teeth	Gravel and recreational road	Slightly slower shifting
Long cage with clutch (MTB)	Up to 46 teeth and more	MTB and gravel 1x	Hangs closer to the ground
Electronic	Same limits as mechanical	Those who want effortless shifting	Battery to charge, own system

Always check the maximum on the derailleur’s packaging or manual.

Choose it if

You ride a road bike with Di2 and want to replace the rear derailleur
You are working on an electronic 11 speed Ultegra drivetrain
Your derailleur is bent, damaged or worn so that it no longer shifts well.
You are fitting a wider cassette and your current derailleur cannot take it.

Choose something else if

You use mechanical shifting, as this derailleur needs electronic control
Shifting is a little vague: a new cable, new housing and an adjustment often fix that.
You do not know which shifter or cassette you have. The wrong brand or number of speeds will not work.

How to fit a rear derailleur

Check the hanger
The hanger must be straight and match your frame. A bent hanger makes even a new derailleur shift badly.
Bolt on the derailleur
Tighten the mounting bolt with a hex key to the stated figure, usually 8 to 10 Nm.
Route chain and cable
Thread the chain through the cage and size it. Clamp the cable with the chain on the smallest rear sprocket and the shifter in its lowest position.
Set the limit screws
The H and L screws keep the chain from jumping past the end sprockets. Set them so the chain runs freely.
Fine tune and test
Shift through the gears and adjust cable tension at the barrel until every step is smooth and quiet. Also check the derailleur cannot hit the spokes.

Good to know

Check that your Di2 system and battery are compatible
Note the SS cage type and the cassette range it accepts
A derailleur hanger is designed to bend so the frame survives. Replace it if it is bent. Take a spare on trips.
Check the maximum sprocket and the capacity: a cassette that is too big can damage the wheel or the chain.
Brand and number of speeds have to match the shifter. A mix of Shimano and SRAM usually does not work.
Oil the pivots lightly and clean the jockey wheels now and then. Worn wheels cause noise and poorer shifting.

What you get

Why a new derailleur?

How the types compare

Choose it if

Choose something else if

How to fit a rear derailleur

Check the hanger

Bolt on the derailleur

Route chain and cable

Set the limit screws

Fine tune and test

Good to know

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