Interchanging Ultegra & 105

Age has now forced me to considering moving to a 32T rear cassette :'( I have a Ultegra di2 6870 11sp rear derailleur and will need a new cassette and change the cage. Is it OK to put on a new 105 11sp cassette rather than the ultegra? The other confusing thing is I see lots of adverts for the GS inner cage plate that I will need to buy (my existing derailleur is a short cage) but never an advert for an outer cage. This doesn't make sense to me - surely the majority of purchases will be for both!


  • 105 cassette will work just fine, but yeah, might need to consider a different cage for the mech if you're going with a 32t
  • masjer
    masjer Posts: 2,558
    You can purchase the inner and outer gs cage here:
  • super_davo
    super_davo Posts: 1,134
    6870 short cage is rated to 28T but pretty sure you'd get away with 11-30 if you wind out the B screw - I have on my 6800. 11-32 would be pushing it though.
  • Many thanks to you all and safe riding.
  • lesfirth
    lesfirth Posts: 1,382
    I have no experience of Di2 but I don not think that matters.
    On mechanical rear Shimano mechs the difference between a "Short cage " and "GS" is not simply the cage. The body of the mechs are different.
    Fitting a longer cage to your mech. will increase chain wrap i.e. the amount of slack chain it will take up but will make no difference to the size of the biggest sprocket you can use.
  • trevor.hall12
    trevor.hall12 Posts: 416
    edited March 2023
    Put on a wolftooth roadlink for 20 quid ,you'll get upto a 34 with your existing set up with minimum cost
  • whyamihere
    whyamihere Posts: 7,702
    Roadlinks don't increase capacity, so the likelihood is you'd be left with either a completely slack chain in small-small combinations or have to run the chain too short for big-big. They also negatively impact shifting performance. There's a few scenarios where they might be a good idea, but not many.
  • mrb123
    mrb123 Posts: 4,614
    Think I'd just buy a GS rear derailleur and sell the old one on Ebay.