What compact cranks are compatible with Dura-Ace 7800 BB cup

blorg Posts: 1,169
edited February 2009 in Workshop
I have a Dura-Ace FC-7800 53/39 crankset and want to stick a 50/34 compact on for the Marmotte. Ideally I'd like to do this without having to change the bottom bracket. Are Shimano integrated cranksets my only option here (in which case I think I'd go for Ultegra SL given that the new 7900 compact is crazy expensive.)

As an aside- would 50/34 front work OK with a 12-27 rear cassette? Short cage RD-7800-SS rear derailleur. I have the 12-27 on at the moment with the 53/39 front and it's working fine. My feeling is that 50/34 with 12-27 will be 2t out of spec for the RD but should work OK? Rated capacity is 29t which is what I have at the moment but (50-34)+(27-12)=31t.


  • redddraggon
    redddraggon Posts: 10,862
    All shimano Hollowtech cranksets and FSA megaexo cranksets are compatible with the DA Hollowtech BB
    I like bikes...

  • Pirahna
    Pirahna Posts: 1,315
    Rotor Agilis.
  • blorg
    blorg Posts: 1,169
    Thanks guys, exactly what I needed to know. You have made what was going to be an easy decision (Ultegra SL) into a horrendously complex one, off I go to consider carbon FSA and Rotor :D
  • John.T
    John.T Posts: 3,698
    50/34 and 12/27 works fine with a short mech. I have it on 3 bikes with no trouble at all. Just make sure you run the chain as long as possible. The bottom chain run should just clear the small tab on the mech cage when on small/small. I can use all gears on all bikes. (Avoid extreme cross over as usual).
    Just go with Ultegra SL. It works as well as DA and is not much heavier. Looks better IMHO.
  • blorg
    blorg Posts: 1,169
    Thanks for that John, I should have just gone for Ultegra SL all right, when I was looking last week this cost around £120 and now it has gone up to £180 most places. Few cheap places left but they have expensive delivery to Ireland. Any opinions on the R700 crankset vs Ultegra SL?
  • maddog 2
    maddog 2 Posts: 8,114
    I run a R700 and I've fitted the SL to a mate's bike.

    Nothing between them, except the finish of course. I prefer the SL looks but mechanically they are very similar.
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • jxohn
    jxohn Posts: 38
    I did exactly the same as you went from a 53/39 to a compact with 12/27 on the rear. The only thing I had to do was shorten the chain by a few links and lower the front derallieur a little. Has worked fine for the last 2 years