[Jasonhenley]

Hi

I have a Cannondale Synapse with Ultegra Di2 6800 11speed with a 11/32t and I think this is the medium cage, with the front chainrings being 50/34 (Cannondale Spiderring)

I am looking to change this to:-

11/28T or possibly 11/25T along with

52/36 or 53/39 up front

By my calculations, but I might be wrong I wont need to change the rear mech as it will cope with both combinations?

http://bike.shimano.com/content/sac-bike/en/home/road/shifting—braking/rear-deraileurs/rd-6870-gs.html

Could somone please double check for me as I am a bit of an amateur on this part?

Many thanks

 

Topic

[Anonymous]

I agree that the GS should

I agree that the GS should able to handle a 25T, but a shorter SS cage may allow a sharper change due to less flex?

I guess I’ll find out.

BTW it’s the SS that is limited to a 28T

Why there are different springs for each cage length beats me. The spec only needs the one with the stronger coil rate to keep chain tension at its highest.

[Anonymous]

I’ve got the same bike and

I’ve got the same bike and the rear mech is the long cage (GS) version.

[url]https://www.paul-lange.de/index.php/de/explosionszeichnungen.html?file=files/paullange/07_Service/04_Downloads/Shimano/explosionszeichnungen/RD/RD-6800-3608B.pdf[/url]

I’m also going to swap to the 11-28 set as I  never use the 32 sprocket and the gaps between some gears is very noticeable. Up front will be 50/36.

The difference between long (GS) and medium (SS) cage 6800 RDs are just two side plates and a spring according to the part numbers, so I am going to buy these parts and convert the current RD for about £32 (SIS Cycles).

Part numbers are:

Spring assembly Y5YC98050 

Inner plate Y5XH08000

Outer plate Y5YC98070

 

SuperP – there are two springs in the RD and one is specific to whether it is a medium or long cage. I presume a stronger spring is on the GS long cage to keep tension on the longer (heavier) chain length needed.

If so then I’d question whether  the SS cage spring is needed if I already have the stronger of the two. Going from the medium to long cage may neccesitate the beefier spring (if it is really different).

As for running the SS cage on a 32 sprocket, this may well “work” but I’d be concerned about increased wear and jumping chains.

 

 

[Leviathan]

This isn’t one of those order

This isn’t one of those order of operations things people keep putting on facebook/youtube/buzzfeed?

[The _Kaner]

(50-34) + (32-11) = 16 + 21 =

(50-34) + (32-11) = 16 + 21 = 37T

(52-36) + (28-11) or (25-11) = 16 + 17 or 14 = 33 or 30

(53-39) + (28-11) or (25-11) = 14 + 17 or 14 = 31 or 28

Your medium RD is fine for either combo…but if going 11-25 may cause issues by being too big – the link you have shows – Minimum Sprocket Low: 28T, Top: 11T (sure someone will correct if wrong)

The last (31 or 28) can be covered by a short RD.

I ran a 53/39 and 12-30 on a Shimano Ultegra 6700 short RD with no issues

[Author]

Replies