Ultegra Di2 11 speed - 10 speed compatibility

borisface Posts: 273
edited July 2014 in Workshop
I've just invested in a scott foil with 11sp ultegra Di2, not got it yet. I have a couple of pairs of 10 speed shimano wheels which I understand will not take an 11sp cassette without, at least, re-dishing. The query I have is that if I swapped the chain for a 10 sp and used a 10 sp cassette would the levers/rear mech function correctly ie is it backwards compatible? Or do I have to use 11 sp all the time?



  • Bar Shaker
    Bar Shaker Posts: 2,313
    You can upgrade Di2 10 speed to 11 just by changing the rear mech so I would expect the opposite move to work for you.
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  • borisface
    borisface Posts: 273
    So, with a 10 speed wheel, use an 11 cassette with one sprocket removed and insert 2.54mm spacer on spoke-side. Great a couple of quid and we can all still use our fast 10sp wheels.
  • tomhammersley
    tomhammersley Posts: 107
    FWIW, I've tried a similar thing recently.

    Went from 10 speed Shimano to Ultegra 6800 (mechanical). I used it with a 10-speed cassette (Tiagra 4600) for a while until I got my proper 11sp wheel built up. It worked... well enough. It would slip a few times, but that was with a worn chain and cassette so I can't be sure how much was down to wear vs bodging. It was certainly useable and I used it for commuting for a while till I got my 11 speed rear wheel built up.

    I basically just set up the shifter to have one spare click at one end of the cassette. The science is that Shimano 10 speed spacing is 3.95mm (I believe), and Shimano 11 speed is 3.8mm or 3.85mm (not sure which). So, worst case you're 0.1-0.15mm out per shift - well within the guide jockey wheel's movement. Now you have to multiply that up by the number of shifts. So that's either 5 * 0.1mm or 10 * 0.15mm depending if you index it from the centre of cassette or one end of the cassette, for worst- and best-case numbers. 0.5mm-1.5mm maximum error. It seemed to work.

    I have another bike with 11 speed DI2, but I never tried the experiment with DI2 - I didn't want to "bodge" my best bike!

    I now have the 6800 commuter running on an 11 speed cassette and obviously it is substantially better than the 10sp bodge. So regardless of whether it works, the proper set up is a substantial improvement.
  • Did anyone find the answer to this one?

    My question is similar to the first. I am thinking of upgrading my TT bike to Di2 6800, but I have 2 x TT Rear wheels that are both 10 speed Shimano. Would the 6800 Di2 RD work with the 10 speed cassette?

    The other work around that i know of is to change the free hub bodies on the Zipps to Campag 11 speed and run a Campag 11 speed cassette, as I don't think Zipp 11 speed have got around to making replacements for the pre 2012(?) wheels yet. Also not so keen on this option as its probably around £100 to sort out each wheel!

    After that the more simple question is what chain would I use? Does a 10 speed chain fit into a 11 speed RD?

    Many thanks
  • Bar Shaker
    Bar Shaker Posts: 2,313
    I wouldn't use a 6870 rear derailleur on a 10 speed cassette. You would need to set the limit screw to stop it falling off the smallest cog and if you shifted against this, it continues trying to push for a while before giving up. Unless counting all the time, you could end up damaging the RD. At best it would be hassle when all you want to do is belt down a hill.

    A better and cheaper solution is to buy a 6770 RD and fit this when you want to use your 10 speed wheel. I've sold two recently on eBay, a tatty one for £50 and a very good one for £90, both in perfect working order. The prices felt about right and for £50 someone has a perfect solution to your problem. The 6770 works fine with a 6870 Di2 installation, just as they work the other way round.

    You need to be running v2.2 of eTube to swap between RDs.

    An 11 speed chain works with a 10 speed cassette and chainring but it doesn't work very well the other way around. It will work but will be noisy on the cassette.
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