Well I finally took the plunge and fitted a Sram PG 1170  11 speed   11-36 T  cassette and new chain to my road bike yesterday . Running on Ultegra  Di2  RD 6870 .

I took it for a test ride and it works really well . The only "issue" it has is that it rumbles a little bit when back pedaling in the 36 T cog , but I would never normally do this anyway .

I tried B screw adjustment but it doesn't make any difference . Even putting a longer B screw in backwards as some of the on line help forums say doesn't do anything, so I'll live with it . It's really good up 15% +     

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Do you have the medium cage dérailleur or the standard one?

Hi Paul ,, I'm sot sure if it's a medium cage or a standard derailleur . The only identification on it is RD 6870 .  I changed the cassette from  11-32  to  11-36.

I don't know how you tell the difference between  the medium and standard derailleur  without having the two together to compare.  

A friend who I sometimes ride with did the same thing a few months ago and we tried his back wheel with the 11-36 on my bike and it worked ok . I will see him next week and work it out.  

Rear d looks like a medium cage to me. I would be very surprised if a standard short cage would work with a 36T.

Can also depend on the hanger design.

Do a side shot of the RD.

From this angle it looks like a medium cage.

Another option is XTR di2 with a 40/42 cassette.

Here is another side shot. This is all a big learning curve for me.  Thanks a lot for your help. 

Pete, there are basically three types of rear derailleur. Short cage is more or less the standard on road bikes and gives crisp changes to close ratio cassettes, but usually limited to a max of a 30T on the back. Medium  - - GS in Shimano terms - - can handle at least a 32T and possibly a 34T. Long cage is almost universal on MTB and can handle a very wide range of ratios. I have a GS with a 32T on one road bike and an MTB XT Deore long cage on another road bike, also with a 32T This long cage could also easily go up to a 34T or more.   

One has to remember that Shimano's recommendations are based on horizontal drop out frames vs the latest vertical drop out frames.

Give it 3-5 years and shimano will update there data.

Ive seen a few bikes now handle 32cassettes with DA9000 and DA9070 SS caged rear mechs.

That is a GS for sure. 

Can you take a photo of the B screw for us. Showing how much it is wound in.

The B screw was wound in as far as it would go with the 11- 32 T cog I started off with , so I found another longer  same thread screw  and put it in backwards (upside down) .  There is still a bit more thread left , but  the hanger "angle" where the screw sits on won't be correct . (it's hard to explain) .

I'm thinking of making another hanger about 3 or 4 mm longer .

Thanks for your help  Pete

It's not easy to take a good shot of , there's too much "junk" in the way ! 

Sorry about all the dirt ,, just got back from a ride .

Looks like a GS -  long cage , not SS - short cage.

Measure the length of the derailleur arm, you can then compare it with others easier.

GS with the longer cage arm looks more akin to a MTB derailleur, SS cage arm is very short, the 2 derailleur cogs are fairly close to each other.  

I've just installed this derailleur hanger extender and been for a test ride up some of my local hills , and no more rumbling of the 36 T and the top cog . Took less than 5 minutes to install . Just wish I had it yesterday on Amy's ride .   http://www.wolftoothcomponents.com/collections/cassette-cogs/produc...

Question Pete.

Do you find going all the way up to a 36 helps your speed when hill climbing?
Allows for a natural cadence rate but you go faster?

Im running a 39/53 front and an 11/25 on the back.
Im a strong enough rider but would like to start having a good crack at some uphill times (strava flog...)

Im seeing guys spinning on dinner plates at the back and wonder where the improvement comes from?
Or is it an effort thing. The same pace but much easier on the bikes biggest engine.

Cheers
Benny

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