Barry2 

Has anyone already gone to 11-36 (or bigger) with an RD-R8050-GS
What did you use for the Cassette.


Thanks

Barry




SRAM PG-1170 11-36 might work
11,12,13,15,17,19,22,25,28,32,36

Iride01 

Why don't you consider some of the di2 mountain bike stuff instead of the road bike stuff. If you already have Ultegra or DuraAce STI's, I don't know what the implications are for that. Maybe someone else does.

But if you find a 36 tooth Shimano compatible cassette 11 speed cassette, I suppose it can't hurt to try it. Might need a hanger extender. Might want to consider something with less difference on the front than the max of 16. If yours is a 53/39 front, then you might be good with that.

Barry2 

Because I just swapped the R8050 SS for a GS two weeks ago.
And staying married requires at least 6 months per Di2 RD purchase.

Barry

Acraick

I've been investigating this myself recently and couldn't really get a good answer apart from 'it technically does work but we wouldnt recomend, but give it a go for yourself' (the cost to do it with the most chance of success would be a new chain, roadlink and casette).

Worst case you seriously damage your wheel, hanger and di2 deraileur when going near the large to large combo and tearing off the deraileur into your back wheel (which di2 might prohibit you doing depending on what software and hardware versions you have).

Below is a good source of guidance apart from the fact they want to sell you the roadlink which some people said wasn't required and I think they are also being conservative regarding the largest rear casette possible.

wolftoothcomponents.com/products/roadlink

What confused me initially was the max deraileur capacity they talk about. Apparently this is the maximum number of teeth you can have taking into account the front and rear combos.
You can calculate this using the common formula they provide. Also confusing is that the different rear di2 derauileurs (ultegra, gravel, mtb) have different max capacities which dont seem to make sense.
I suspect there is also more tollerence in their 'max' capacity rating anyway. It probably comes down to how happy you are having the rear deraileur stretched out in some gear combos and how much chain slack you're willing to put up with.

The other interesting finding is you can swap any of the newer di2 rear deraileurs and they're compatable assuming all your software (all the components need to be patched) is up to date.

Sorry not a great answer but hopefully it might save you some research. I'm after the ellusive 42 tooth rear casette on a Shimano compact chainring combo (well out of spec) but once my parts arrive and I test it I think I'm going to be disappointed.

Barry2 

TLDR: Today I've purchased a SRAM PG1170 11-36 cassette and new Ultegra (126 link) 11sp chain. I am going to try this.


You are correct Rear Derailleurs are rated with two numbers and RD-R8050-GS are shown below.
Max size of Rear Cog = 32
Max teeth difference. 39

Weird thing is that if you go with the apparently Shimano blessed 50/34 & 11-34 you break the cog rule and max out the teeth rule.
Max size rear cog = 34 (2 over spec)
Max teeth difference 16+23 = 39 teeth

With the 11-36 we stretch the specs a little further.

COG SIZE
A 36 cog is 4 over spec... however the diameter of a 34 vs 36 cog has to be so close it makes little difference.

TEETH
This is the ability of the RD to take up slack.
If you watch the Park Tools chain length video, they show you where to cut a chain to length.
If the cut falls in the wrong spot, they have you ADD 1 link to get to the correct spot.
I use this method to size my chains so that big-big is possible without damage and without relying upon the cross-chain protection built into Di2 stopping big-big.
It just so happens that two weeks ago when installing the Shimano 11-34 I did actually have to add this additional chain link.
So my current RD/cassette is likely already operating with the correct length chain if the YouTube video is to be believed.

Give me a day or two and I'll report back on the results.


I did find a YouTube video that has done this, (see below)

55tele

My bike is a Zinn Clydesdale….IT DOES HAVE A HANGER EXTENDER standard from the builder.

I’m running the Ultegra RD8050 DI2 GS rear with SRAM 1170 and 1130 cassettes on two sets of wheels, both are 11-36. Front rings are 50/34….This was the standard setup from Zinn for the Clydesdale Team ….

No issues other than the outer front cage very slightly rubbed when in 34/17…only under heavy load and it was adjusted out with ETube software at +10 in low adjustment….this was a trim issue….

My chain is an SRAM 1130 at 116 links…You might want to investigate either the 1130 or 1170 chain as there are reports SRAM cassettes chew the hell out of Shimano chains….

My setup is quiet and shifts great…

Barry2 

Thanks for the info.
Glad to hear it’s quiet.
Do you know who’s hanger extender they used?

Barry

55tele

No…likely made for them for this frame…..

Barry2 

I have installed the PG-1170 11-36 with my existing RD8050-GS and 34/50 R8000 cranks.
I put 70 miles on it this weekend and despite being outside of Shimano spec’s, it works great. Shifting is smooth, and although some of the tooth jumps are larger, I can get used to those.

Using the Park Tool (big-big+2rivets) method to determine chain length resulted in same length as my 11-34 Shimano cassette.

here is the weird part. I expected to be able to climb slower saving watts.
im actually climbing a little faster due to the higher rpm being less tiring.

Note: Shimano 11-34 required the supplied spacer against the hub. SRAM PG-1170 does not come with spacer and it’s NOT required.
My B screw was set generous for the 11-34 and did not require adjustment for 11-36.
FD needed no adjustment, RD needed a little, but that’s to be expected.
Di2 E-Tube has no 11-36 option. You will need to calculate your ratios and set your change points (full sync) for yourself, mine shown below.

Barry



Just a quick UPDATE JULY 2022
This 50/34 & 11-36 setup has none 3000+ miles without issue.
My buddy did the same to his non-Di2 R8000 also without issue.

All the best

Barry