Shimano’s recently announced Tiagra 11-36T rear cassette has got me wondering if it’s possible to shoehorn that baby monster onto my touring bike that’s currently fitted with an R8070 setup running 53/36T (not a typo) chainrings up front. I’ve got an 11-34T out back, but hoping that I could get that Tiagra cassette on instead, for a little more headroom.
The current setup is already pushing the RD’s capacity a wee bit, and I’m wondering if the additional 2 teeth might be beyond the RD’s capabilities. If so, are there any aftermarket pulley cage options for the RD?
I’ve got that derailleur and I’ve used it with a SRAM 11-36 cassette on two different bikes with absolutely no issues. That’s no guarantee that it will work on every bike though.
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Thanks @Adrian_Leggett. Fair point on whether it’ll work on my bike (or not), but would you also happen to be running 53/36T chainrings as well?
If your intention is to increase the clearance between the largest cog on the cassette and the guide pulley, then this is a bit tricky. However, if your intention is to reduce the amount of spring tension the cage experiences during extreme gear combinations (big ring-big cog), then a longer cage length would help with that.
This is because the rear derailleur’s cassette capacity (the largest cog it can handle) is determined by the 4-bar linkage mechanism’s geometry, whereas the cage length dictates total chain capacity. A longer cage is unlikely to provide additional clearance and capacity as long as the guide pulley axle is on the same axis as the rotational axis of the cage. Perhaps a pulley cage that has it’s guide pulley axle axis offset away from the cage’s pivot point, such that the guide pulley moves further away from the cogs as the cage pivots when shifting to the larger cogs would work. I’m not sure how this affects shifting quality, though.
Bottom line: a longer cage in itself would not increase the rear derailleur’s cassette capacity. You’ll most likely need to source for a longer hanger (Wolftooth Goatlink or similar) if clearance between the guide pulley and 34T cog is tight to run a 11-36
I used 52/36 for awhile and that was fine.
I should add, I use Syncro shift so I’m never in big ring and big cog.
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I’m rarely in that combo as well, but when riding with panniers and whatnot, the overall weight can tip over 20kg. That 1:1 combo would do nicely, once the gradients start pitching upwards and longer. These days, the bike also does double duty as my regular ride, so I’m a little hesitant to swap out the front chainring combo, since it gives me a fairly comfortable spread. It’s the cassette that I’m hoping might give me a little more headroom, but I’m unsure if a 53/36 combo with an 11/36 out back has been attempted before.
Thanks @Adrian_Lim.
I’m actually looking to see if I’m able to increase the bike’s overall gear range, without having to swap out the front chainring setup. So that pretty much leaves the only option being a cassette change to get more headroom at the low end (big chainring - big cog). A 1:1 combo would do nicely, and a little better than the 34T I currently have right now.
Not inclined to a Road Link at this stage, unfortunately.
Big-big is what want to avoid. The increased range comes from small ring-big cog which isn’t a problem.
Oh yes, you’re right. My head was in the wrong place. 
I’ve run a 50/34 front and a 30/46 front with that Sram 11-36 cassette and no issues for me from a ‘medium cage’ Ultegra deraileur. On an early gravel bike, I had a 11 speed 5800 series rear derailleur which I put a MTB Dynasys rear derailleur cage on to give me a super wide range of 50/34 with an XT 11-40 which was not available at that time, this was before Shimano even offered GRX or an 11-34 road cassette.
It was harder to get appropriate gearing back then, if you wanted to stay with twin ring front and road shifting and wanted more than 9 speed (which is where Shimano started to differ their cable pull for road and MTB shifters limiting compatibility between road shifters and MTB derailleurs)