Dura Ace 7800 / 7900 combo?

hubcap
hubcap Posts: 163
edited November 2012 in Workshop
I have done lots of searching but haven't found a conclusive answer to say whether the set up of mixed Dura Ace that I would like to run will work okay.

I basically want to have 7800 shifters, brakes and front / rear mechs but combine them with a 7950 compact chainset and 7900 chain. I know that 7800 didn't come as a compact option so I'm not sure if this set up will work, the Shimano compatibility chart says that the 7950 crank runs with 7900 shifters and front mech.

Has anyone tried this combination or can offer advice as to whether it will actually work or not?

Thanks :D

Comments

  • Monty Dog
    Monty Dog Posts: 20,614
    No problems what so ever - chainsets and chains are universal across transmissions using the same number of gears, regardless what different brands tell you. The only exception would be Shimano AX from 1981 which used a 10mm pitch chain - everyone else used and continues to use 1/2"
    Make mine an Italian, with Campagnolo on the side..
  • hubcap
    hubcap Posts: 163
    Thanks Monty, I wonder why the Shimano compatibilty chart shows them as not being compatible then?

    I did also read somewhere that 7800 wouldn't run with an inner ring as low as 34T, someone said it wouldn't go beyond 36T, do you reckon that's not true?
  • cycleclinic
    cycleclinic Posts: 6,865
    A 130 BCD chainset can only have a 38T inner ring as it smallest.

    Where would you get Shimano Ax chains now them?
    http://www.thecycleclinic.co.uk -wheel building and other stuff.
  • hubcap
    hubcap Posts: 163
    Thanks. So because the 7950 compact has a 110 BCD there won't be a problem then?
  • tonye_n
    tonye_n Posts: 832
    Hubcap wrote:
    Thanks. So because the 7950 compact has a 110 BCD there won't be a problem then?
    No problem with this set up.
    I run 7800 front mech, shifters, brakes with Ultegra 6750 (110 bcd) compact chainset, 6700 chain. No problems.

    The distance b/w the chainrings on the new Shimano chainsets (7950, 6750, 5750 et al) is a little bit wider spacing than the previous generation (7800 etc).
    Therefore you just ensure that you adjust the limit screws on the front mech accordingly to allow for this.
  • Mccaria
    Mccaria Posts: 869
    Hubcap,

    I road pretty much that set-up on a bike all this summer - only difference being I prefer KMC chains to Shimano. The 7950 with 7800 shifters and derailleurs was no problem at all. Also the 7800 rear derailleur is only supposed to work up to 27T on the cassette, but I used a 12-28 cassette without issue.

    Main 7800/7900 compatability problems are STI levers and brakes (different pull ratios, it will still works but Shimano calls this B level compatability), and front derailleur (7800 FD is designed for trimming in both big and small rings whereas the 7900 FD has trim in only the small ring so the 7900 left STI lever has one fewer shift position).

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