Forum home Road cycling forum Workshop

Using a 32 sprocket with a short-cage Ultegra derailleur

g00seg00se Posts: 2,221
edited October 2016 in Workshop
Hi,

A technical question on running a cassette out of spec with a new 6800 SS rear mech (the short cage version).

The spec says it has a chain capacity of 33 and a max sprocket of 28 teeth. This ties up with running the widest 11-28 cassette with a compact chainset (34/50 or 36/52). Both of those need a capacity of 33.

Now, this will be on a cross bike with a chainset using rings of 46 and 36. That means the front capacity is down to 10 teeth (from the 14 of a compact). So running this with an 11-32 cassette will theoretically still have the capacity under 33 (it will be 32).

So all that remains is whether the short cage mech will clear the bigger sprockets - but looking at the parts sheet:

http://si.shimano.com/php/download.php? ... -3608A.pdf

The body of the short cage version is the same as the medium cage version (which will accommodate the 32) - all that appears to differ is the length of the cage (for an increased capacity). Which make me think it should work? I suppose the design of the medium cage could place the top jockey wheel further from the cassette, but it superficially looks in the same place on the parts sheet.


Have I missed anything obvious or has anyone tried it?

The other options are to use a 30 on the back but they look impossible to find in an 11-speed cassette without spending a fortune. Alternatively, swapping the 36 chainring with a 34 - but I prefer the closeness of the current rings and the inches gained with the smaller ring is not the same as with the cassette.

Posts

  • drlodgedrlodge Posts: 4,825
    I reckon it might just work, if it doesn't then this little device should solve the problem. I just bought it to go with a 11-32 cassette on my Campag Super Record setup on the Rourke. The problem I may have is the opposite of you - chain take up may not be sufficient.

    http://gearmechhanger.com/S14-Alpe-DHuez-Road-Fairy
    WyndyMilla Massive Attack | Rourke 953 | Condor Italia 531 Pro | Boardman CX Pro | DT Swiss RR440 Tubeless Wheels
    Find me on Strava
  • g00seg00se Posts: 2,221
    Campag always seem to understate the capacities - fingers crossed that works for you.

    I just googled a similar US device (called a Wolftooth Roadlink) http://fitwerx.com/wolf-tooth-roadlink- ... er-review/ and it suggests there may be issues with cross-chaining a short cage mech - so worth checking on the SR mech you have.
  • drlodgedrlodge Posts: 4,825
    Yeh I found the Wolftooth Roadlink first, but availability isn't as good in the UK. I reckon there will be capacity issues either on big-big or small-small depending on how the chain length is set. Will probably err on the side of caution and set the chain length so big-big is OK, then I just have some slack if I accidently go small-small which I never actually use. Better that than ripping the rear of the bike apart!! Its an additional 4 teeth compared to my 12-29, which I guess is only 2 half links (since the chain goes round only half of the cassette) so there shouldn't be too much slack.
    WyndyMilla Massive Attack | Rourke 953 | Condor Italia 531 Pro | Boardman CX Pro | DT Swiss RR440 Tubeless Wheels
    Find me on Strava
  • trailflowtrailflow Posts: 1,311
    edited September 2016
    Yes that's correct. The difference between the SS and GS RD is not just the cage length but the angle of the cage travel. So it keeps the upper pulley as close as possible to aid shifting.

    R2u8gHn.gif

    So the short cage RD pulley will be immediately be too close for a 32 cog and if your hanger is on the short side the problem is worst.

    Whether or not the upper pulley will touch the cassete cog excessively all depends on the length of your hanger. Some are shorter/longer than others.

    I am currently running a short cage DA9000 RD with a 32t cassette and a 33/46t chainset. The b-screw on the RD is around half way in. The way i set it up, i put the chain on the 32 cog and inner chainring. Then spin the crank backwards and listen to the upper pulley make noise on the 32 cog. Then i keep winding the b-screw in (make sure its all the way out to start off with), half turns until the noise is gone. I have found if i keep turning the b-screw more than necessary it can have a negative effect on the RD shifting quality. So i try to find a balance and try not to over do it.

    Big/Big is the only combination that im unable to use. But i have my chain cut as short as possible. If i go into that gear the RD is stretched out as far as it will go and i can feel the chain resist movement alot more. And theres alot more noise.

    The next cog down is not totally silent either but is still usable. So it gives me an audible warning of which gear im in.

    The third,fourth etc cog is fine

    The Small/Small combo is fine.
  • g00seg00se Posts: 2,221
    The thing is, the parts of the parallelogram on the SS and the SG are the same. So you would think the travel would be the same?
  • trailflowtrailflow Posts: 1,311
    There will be a slight variation in the parallelogram linkage to accomodate the further distance.
  • The RookieThe Rookie Posts: 27,748
    how CERTAIN are you of that? In the past I've compared them and apart from the cage halves the main body parts are identical. More likely the longer cage just moves the upper jockey a bit further away, the. As the cage maintains chain tension it will move the jockey closer as it rotates around its pivot.

    Sort of related, my MTB is running a short cage 9sp XTR rear mech with a stated max sprocket size of 34, it's on a wide ratio 11-40 10s cassette and works perfectly (using the right shifter).

    Shimano often only quote what it's expected to run on not what it actually can run in, personally I reckon it will be fine.
  • trailflowtrailflow Posts: 1,311
    I cant see how else it would be achieved. The angle of travel would need to be on a different trajectory for the top pulley to reach the distance of the 32t cog and to clear it. All that would be needed is a very small adjustment of the size of the parallelogram. Only a very small amount of repositioning would allow for that extra distance. Could that be noticed from a visual comparision of each RD ? Im not sure it would be that easy without some very precise measuring.

    How can you be certain the main body parts are identical ?
  • g00seg00se Posts: 2,221
    Looking into it further, I think trailflow is right. In the Shimano exploded parts diagram above, only the cage components differ - but looking again, the actual main body of the mech is not assigned a part number - so it's inconclusive as to whether they are the same or not.

    And just found this were someone has measured the parallelogram of the SS and GS 6700 version - and they do differ:

    https://www.reddit.com/r/bikewrench/com ... than_cage/

    So it looks like I'll have to just get a new chairing for now - and think about replacing the mech in the future.
  • The RookieThe Rookie Posts: 27,748
    trailflow wrote:
    I cant see how else it would be achieved.
    Well its not achieved anyway, the upper jockey is always further away in top than lowest gear and that includes my commuter which has an MTB mech on a 12-28.
  • With a 11-32 I was able to clear the rear pulley from contacting the 32 by using a longer "B" screw (4mm x 12MM) with a SS rear derailleur BUT the SS didn't provide enough chain wrap.
  • svettysvetty Posts: 1,904
    g00se wrote:
    Looking into it further, I think trailflow is right. In the Shimano exploded parts diagram above, only the cage components differ - but looking again, the actual main body of the mech is not assigned a part number - so it's inconclusive as to whether they are the same or not.

    And just found this were someone has measured the parallelogram of the SS and GS 6700 version - and they do differ:

    https://www.reddit.com/r/bikewrench/com ... than_cage/

    So it looks like I'll have to just get a new chairing for now - and think about replacing the mech in the future.

    Sorry if I'm being obtuse but why not just run a medium cage 6800 rear mech and stick with the 36 small ring? Alternatively try fitting your SS mech with the GS cage? Either way you get the ratios you want......
    FFS! Harden up and grow a pair :D
  • g00seg00se Posts: 2,221
    Cost
  • svettysvetty Posts: 1,904
    g00se wrote:
    Cost

    Inner and outer cage plates cost £22 a pair........

    https://www.sjscycles.co.uk/search/?ter ... eries=6800
    FFS! Harden up and grow a pair :D
  • g00seg00se Posts: 2,221
    Svetty wrote:
    g00se wrote:
    Cost

    Inner and outer cage plates cost £22 a pair........

    https://www.sjscycles.co.uk/search/?ter ... eries=6800


    But if the clearance is down to the parallelogram, it's not just a matter of changing the plates - I'd need to change the whole mech. Also, if it was just the cage, the SS has enough capacity for a 11-32 with a 46/36 chainset anyway.

    Thanks for the advice folks - I've gone for the new 34 chainring just to be safe.
  • svettysvetty Posts: 1,904
    g00se wrote:
    But if the clearance is down to the parallelogram, it's not just a matter of changing the plates - I'd need to change the whole mech. Also, if it was just the cage, the SS has enough capacity for a 11-32 with a 46/36 chainset anyway.

    Thanks for the advice folks - I've gone for the new 34 chainring just to be safe.

    Accepted that the parallelogram wouldn't change (and that total capacity isn't the issue) but the longer cage should facilitate the change from a 28 to a 32. I seriously doubt that this plus a B-screw adjustment wouldn't work with the 11-32.
    FFS! Harden up and grow a pair :D
  • davidofdavidof Posts: 2,578
    g00se wrote:
    Hi,

    A technical question on running a cassette out of spec with a new 6800 SS rear mech (the short cage version).

    The spec says it has a chain capacity of 33 and a max sprocket of 28 teeth.

    Are you sure the max isn't 30T these days? I run a 6800SS with a 32 sprocke and a compact c/set no problems. I never even thought about it.
    BASI Nordic Ski Instructor
    Instagramme
  • FWIW, I have an older Dura-Ace 7700 RD (short cage) on one bike that handles an Ultegra 6700 12-30 10-speed cassette without any problem. There is a 12 tooth difference in the front chainrings (48-36), and I can run both small-small and big-big, though in the normal course of events I don't use those gears. When on the small chainring and 30t sprocket, there is about 3mm clearance between the ends of the teeth on the sprocket and the top jockey pulley. The B adjustment screw is nearly all the way in.
Sign In or Register to comment.