I don't know how to tell Jim. It came on a new P2 I bought last year. Everything seems to shift fine except for a very slight rub after moving the B screw all the way down.

If you have an SS short cage, the distance between the pulleys (center to center) will be about 55mm. The GS medium cage will be about 85mm.

Well crap. It looks to be a lot closer to 55m than 85mm. I'm assuming I should err on the side of caution and put my old cassette on for tomorrow's ride and go talk to my bike shop next week?

I would order a new rear derailleur and chain from Backcountry today and install them myself.

That has NOTHING to do with clearing the 32 tooth. It's entirely a b screw issue.

I just worked on a brand new, stock P2 and it had a GS rear derailleur.

Measure it to make sure.

Yes it does.
As the cage rotates forward it changes the position of the top pulley to the cassette.
Different cage lengths rotate different amounts to take up chain slack.
This completely remaps the top pulley clearance for the entire cassette.

I have just set up my tri bike with a Dura Ace 9100 rear derailleur matched to a 11-32 SRAM XG1190 cassette with a new KMC chain and it works perfectly. Took it out today for a 125km ride and was very happy with it.

Incorrect. That specific pulley is in the same position on each derailleur, thus your "top pulley clearance" is the same on either one. The cage rotation can't move the pivot point. Every part on both the SS and GS are identical except the cage length.

That's why you are able to swap cages if needed. That's why you see short cage derailleurs running larger cassettes in a 1x application. The longer cages handle more chain so you can have a wider range in a 2x application. End of story. #letsendslowtwitchmisconceptions

End of story. #letsendslowtwitchmisconceptions.

Now thats a hardcore end to a post. One would have to think you have done your homework, and really know what you are talking about. I suppose i should applaud you, for trying to get rid of some of all the bad info floating around on this forum cause there is a lot of it. However you are probably a major part of the problem by making this kind of black and white statements. There has been a lot of really knowledgable people on here over the years that has left small gold nuggets. but are no longer posting regularly. These kind of posts are probably a lot of the reason.

I am normally not a black and white kinda guy but this time around, you are leaving so much wrong info that is potentially harmfull to others, and you are doing it in a way that makes it seem as if you are telling the end it all truth. Therefore i feel the need to tear your post apart so here goes:

Incorrect. That specific pulley is in the same position on each derailleur, thus your "top pulley clearance" is the same on either one. Nope

The cage rotation can't move the pivot point. Correct but the upper pulley does not sit in the pivot point, so cage rotation will move the upper pulley away from the cassette

Every part on both the SS and GS are identical except the cage length. Oh really..... That info was definately correct 510 years ago when we were talking 5600,6600 and 7800 series. I am 95% sure that it was still correct 5 years ago when we were at 5700 and 6700 series. But Yoy and others here are discussing "modern" 11 sp. 5800 and 6800 series.please take a close look at the picture below. Do you really really believe that what i think is called the P-knuckle in english is the same lenght on these two derailleurs?


That's why you are able to swap cages if needed. That's why you see short cage derailleurs running larger cassettes in a 1x application. Well on 5800 which is what was being discussed as far as i remember you cant even screw of the cage so no changing at all. if you try it on a 6800 you will find that a ss cage on a gs derailleur will put the upper pulley too far away from the cassette to make gear work smoothly no matter what you do to b-tension. I never did try a gs cage on ss derailleur so do not know for sure how it will work but i suppose you would get problems clearing the cassette.





I will now probably go back into hibernation but please do your homework going forward if you want to make that kind of end it all posts.

#playnice

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Disclaimer: I have made a living in bike shops for more than 2 decades, so according to most people on this forum am not at all trust worthy

Dearest Toefuzz,

The bottom line here is that the derailleur that comes stock on the P2 (and most tri bikes) is a short cage model (FD-R5800-SS). It doesn't have enough capacity to go beyond what comes stock on the bike. The derailleur needs to have enough chainwrap capacity to take up the slack in the chain when in certain gear combinations.

Stock P2 configuration: 52-36(chainrings) + 28-11(cassette) = 33 (derailleur capacity needed)

The combo you are wanting to run requires a derailleur capacity of 36 teeth.

Shimano FD-R5800-SS (short cage) capacity: 33t
Shimano FD-R5800-GS (medium cage) capacity: 37t

Too small of a capacity will cause either the chain to be too short (tight) when you end up in the big/big combo and/or too long (loose) in the small/small combo of gears.

Too tight of a chain can tear your derailleur right off, destroying it and your chain at a bare minimum. Too loose of a chain will cause chain slap and dropped chains.

Order a Shimano FD-R5800-GS derailleur, get a new chain and watch this video on how to get the chain sized correctly and you will be all set:

https://www.youtube.com/watch?v=Vg2SoOOrpE8


P.S. "dangle" is incorrect. The GS versions of the road derailleurs have a slightly higher parallelogram angle than the SS version. That is why they can go to a larger sized cog than the SS, but it sacrifices a little bit of small cog shifting quality.

P.S.S. "long cage" is a bit of a misnomer when referred to Shimano road derailleurs. Shimano's road derailleurs come in "SS" (short cage) and "GS" (medium cage) only. The "SGS" (long cage) derailleurs are only available on their MTB series. Shimano likes to confuse the issue even further by using a "-S" or a "-L" at the end of the part name, which actually means "silver" and "black" respectively.

So when I look at competitive cyclist's page for the new dura ace di2 rear derailleur, and it says:

• Accommodates up to a 30t cassette cog

But then Shimano's website lists two specs, one says the same as above, the other says max capacity of 33.


So why do they bother listing a max cassette cog?


If I want to use a 1X setup, should the dura ace work fine with a 50t up front, and an 11-40 in the back? If I'm doing the calculation correctly, that setup requires an rd with a 'capacity' of 29...




Thx!

The angle of the parallelogram of the new Dura-ace is not at an angle that will allow it to track a cog as big as 40t, that is why it has a max spec of 30t.
The top pulley will more than likely hit in 1st gear and be far to far away from the cassette to shift properly in smaller gears.

There is a total tooth capacity which is basically the cage length and there is a maximum cassette cog size which is mainly related to the angle of the parallelogram and where it is located in space due to the P-knuckle length.

If you run within these specs then it is guaranteed to work.
If you go outside of these specs then it may or may not work depending on the position of the hanger, how far out of spec you are, as in you can often push one limitation a little bit and get a workable compromise but push both and it is pretty much a guaranteed failure.

When it comes to anybody posting on Slowtwitch about ways to make it work, then the only sensible reply is to stay within specifications because if they are asking, then they obviously do not understand the compromises made and the potential for damage if outside of recommended specs.

You can cobble together some monstrosities that in the hands of somebody who understands will perform OK, but in the hands of somebody who doesn't, you risk chain drops, chain jams, broken chains, derailleurs and hangers as well as poor shifting.

A new derailleur is bloody cheap piece of mind if you need to run really large range gearing.

Now not addressing this poster.
Ride whatever shit setup you like, but don't advise others to do as well when you don't even understand it yourself.

Understood.

Next question - any issue using the XTR di2 rear derailleur with the di2 TT shifters? Thought I had read online that the XTR would not function if it detected a road front derailleur. But wondering if it will work with no fd, just the tt shifters...

Sram WiFi derailleurs will go 32T as standard.
Brand new Dura-ace (black components) will too as it has changed to MTB style geometry.

Good question about XTR and road compatibility, don't know off the top of my head but a little time in tech docs will answer. You can run it without a FD, so probably can.
Watch this space.

Anybody looking for a wider range should first be on compact cranks.
Then get on 30 or 32 T if need be.
I test rode a 34 X 32 up the hill to my house after servicing and it was a cruise to get up the 22% grade with a way too low seat and I am hovering around 100kg at the moment.
30T should be adequate for even oversize donuts on any Tri course.

http://productinfo.shimano.com/#/com/2.4?cid=C-472&acid=C-473

This suggests that it should work....

lyrrad is correct.. and gives good advice insofar as keeping things within specs. I've seen cobbled together systems that "work", but the owner is invariably unhappy because of shitty shifting performance. You can hack a system to use a really big rear cog (Road-Link, B-Screw mods, etc) but the guide pulley ends up being so far away from the other cogs that shifting performance goes all to hell.

The new XT and XTR derailleurs are good options and are now compatible with the road components:

http://e-tubeproject.shimano.com/...M-CC.3.0.0-01-EN.pdf

You can pair these with a CS-M8000 cassette to get the range that you're looking for. Beware, however, if you go to a 46 large cog, only the "lower end" RD-M8050-GS will work with the 46T version.


I'd recommend the MTB over the road RD's in a 1x setup because they have a clutch mechanism to keep the chain tight enough to stop it from bouncing off of the front ring.

Also, if you really want to do 1x, I'd recommend a "narrow-wide" type front chainring to help prevent dropped chains. SRAM Rival 1, SRAM Force 1, and Wolf Tooth Drop-Stop are proven options.

It's clear you care about the quality of information on Slowtwitch and that's great. The picture you provide is the only real 'evidence' in the post. It does appear to have different dimensions. The problem is that it's an artist's rendering and not an actual picture. Maybe it's perfectly representative, maybe it's not. I know we disagree on this stuff, so I'll just leave some things for other readers and let them decide on their own and let them ruin their own bikes. I don't disagree with 'staying within specs' for most people. 'Within specs' doesn't always work for everybody. I do have enough experience to know what works for racing and a LOT of hands on with the 5800/6800 mechanical series in cyclocross, gravel, road, tri and tt applications. Some would say that I have done my homework. Except on Dura Ace. I don't own any Dura Ace derailleurs (or newest Ultegra 8000), so I won't address those.

If you don't have any interest in reading further, just call Shimano. If you're still working in a bike shop, you have the number. Even lowly consumers like myself are able to call in with tech questions. The number is 800-423-02420. Ask them if you can swap SS and GS cages among 5800 or 6800 rear derailleurs. They will eventually tell you it's okay to swap plates/cages as long as the series is the same. i.e. - 5800 cages/plates won't go on a 6800.

I had a Shimano factory mechanic at Jingle Cross say the same thing, so I suppose this is what I have been basing my info off of the last year. Plus I called in before replying. Maybe the the main body/parallelogram is slightly different between the two. If you poke around where the spring is, you can see a short cage RD has "SS" written in there and a medium cage has "GS" written in there. Visually there's not much other difference. It's pretty hard to find anything definitive on the internet, other than opinions on forums, so I really can't provide more evidence than claiming to have talked to a Shimano mechanic and then some dude who answered the phone there. If that specific evidence of incompatibility existed, somebody would have slapped me with it by now. The ST population is pretty smart and quite sleuthy as well. It's pretty common knowledge that their mountain bike rear derailleurs are quite similar (within models) except the cage lengths, so there's that too. If there's a difference in the main body of these Shimano road derailleurs in discussion, it doesn't appear to be enough to have a meaningful difference in real-world usability.

It's kind of hinted at in the Shimano tech documents below how similar things are. Every associated part is interchangeable. There's not a specific part number for the main body/parallelogram/p-knuckle unit that we're dithering about though. You can't take those apart at all, so having one tech document to cover both types could explain that away. Shimano makes it impossible to match non-series parts. No 10 speed cages will fit on an 11 speed derailleur. 6800 cages won't go on a 5800. Shimano literally makes a new cage attachment design every time to make sure people aren't mixing them. It's sort of strange that the cages are interchangeable between SS and GS if they really don't want you to use them together.



An awful lot of compatibility here. It's still possible that the main bodies are slightly different beyond the stampings, but maybe not enough to make a difference. The tech documents show everything else to be quite similar. My experience has shown no issues with a GS cage on a SS derailleur.

And to the point about a 5800 cage not being removable...

Just like the 6800, the 5800 cage pops right off after removing the stopper pin, rotating/unwinding, and removing the bolt holding it together. There's two holes for your spring to go into. Shimano ships them in the 'lower tension' setting. People in the cyclocross and gravel world put the spring in the 'higher tension' hole to get more chain tension. It's a 5 minute job and makes a world of difference in chain retention. A narrow wide ring, correct chain size and the derailleur in the higher tension setting is a bulletproof cyclocross setup. We have so many people asking about implementing mt bike parts, but I think they would be pretty impressed if they took a Phillips or JIS driver, hey key, and 5 minutes to change the spring hole in their 5800/6800 rear derailleurs. Park Tool shows you how on their website. It's step #7 under Shimano at this link - http://www.parktool.com/...ul#article-section-3.

RZ wrote an excellent response to OP's specific question. The SS vs GS thing matters a LOT in a 2x application. My main point is that it doesn't matter a whole lot in a 1x application and a SS rear derailleur can take a GS cage no problem.

The SS and GS are similar enough that clearing a 32 (or any) cog has more to do with your frame and b screw. Needing a GS cage has to do with how much gear range/chain you need to manage.

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Since we like subjective stuff so much, here's my experience over the last couple years.

I'm a middling cat 3 cyclocross racer, FOP tri rider, crappy road racer, and I would put my mechanic skills up against most.

For 1x, I can say that a SS cage 5800 105 fit an 11-36 cassette with a reversed b screw. It was sort of sucky, but I have seen people ride worse. It was exactly what lyrrad described. The guide pulley is sitting a little further back than intended and the shifting isn't great. You're also not getting the clearance you want on the 36. You should be able to slide a 6mm hex key between the guide pulley and the cassette. A Roadlink cleared this up. The Roadlink is great. It puts the guide pulley in a much better position for better shifting performance. They are a bit more sensitive to hanger alignment, so make sure to use the hanger tool first if you put one on. My secondary cyclocross bike wears an 11-40 cassette with a 105 SS (short) cage RD (in the high tension setting) most of the year. Gasp. It shifts perfectly. Perfect. It has hundreds of gravel miles on it. It rides stuff that rattles your eyeballs without dropping a chain.

My cyclocross race setups are 1x with an 11-32 cassette paired to a short cage rear derailleur. No Roadlink. 6800 on one bike and the same 5800 on another. Great shifting. One dropped chain in two seasons of ~30 races and lots of practice. The mud was so thick it literally lifted the chain off the ring, so it had nothing to do with the derailleur. I had to DNF about a minute later because the rear derailleur and wheel were absolutely clogged with mud and stones.

Road bike - Came stock with 52/36 front and a SS short cage 6800 rear derailleur. Wanted to use an 11-32 cassette for a ride with 12k of climbing and lots of double digit inclines. Replaced SS cage with GS cage to increase the chain capacity. No other changes except a b screw adjustment to clear the 32. There was still a lot of b screw left ever after getting the 6mm of clearance. It worked perfectly and still does. There's no reason to switch back to the short cage unless I'm desperate to save 8 grams...ok, I made that number up.

You can put a GS cage on a SS rear derailleur if you want. I don't know why anybody would put a SS cage on a GS derailleur, but you could.

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I really encourage you guys and girls to try this stuff on your own. Test it in the stand to see if it works instead of trying it for the first time on the road.....or in a race. The points about your chain being too short and ripping off your RD are real. There's a lot more wiggle room for 1x setups. Maybe you'll break stuff. Maybe you'll end up with a setup you love. Maybe you'll geek out on mechanic stuff and really enjoy it. Explore other forums too. Talk to cyclocross (or any race) mechanics - those guys know all sorts of fun stuff.