Dura-ace compatibility questions

Questions:

1)  How do I find out which version of a groupset I have on my bike, I know its dura-ace and pretty sure its 7800 but not sure how to check (is it marked on each component?) bike was bought in 2007.

2)  I suspect its 7800 and cant find cassettes for sale online, there are 7900s and 9000s.  A bit confused by the commentary on various forums around whether 7900 or 9000 cassettes are compatible with 7800?  Can anyone clarify, I want to get a 12-27 to replace the 11-23 I have on now?

Comments

  • Don't know when 7900 was introduced but suspect it was post-2007. 

    7900 is compatible with 7800.

    9000 is 11 speed and thus incompatible.

    Seriously though, I'd buy Ultegra. If you *really* want to haemorrhage cash, then buy Ultegra and post me the difference...... image 

  • It will have the number stamped on the shifters underneath the hoods. Easiest way to tell is do you have internal cable routing or are they external? 7800 has the cables coming put the side and 7900 has them coming out behind the shifter and this enabling them to be wrapped under bars.



    Personally I'd go Tiagra or 105 for value or money. As long as it's 9/10 speed then it won't matter too much. There is a little weight difference but for the extra cash I wouldn't say it's worth going to dura ace level.
  • Rocco. wrote (see)
    It will have the number stamped on the shifters underneath the hoods. Easiest way to tell is do you have internal cable routing or are they external? 7800 has the cables coming put the side and 7900 has them coming out behind the shifter and this enabling them to be wrapped under bars.

    Personally I'd go Tiagra or 105 for value or money. As long as it's 9/10 speed then it won't matter too much. There is a little weight difference but for the extra cash I wouldn't say it's worth going to dura ace level.

    but then Barlist would look a bit of a noob running Tiagra on his Cervelo P3....image

  • I didn't know he was running one of them! Go for the dura ace to match! If they are TT shifters I'm not sure how to differentiate between them, the notes above re: cabling is only applicable to road shifter. Either way the cassette will match and just depends how much you want to spend image
  • fat buddha wrote (see)
    Rocco. wrote (see)
    It will have the number stamped on the shifters underneath the hoods. Easiest way to tell is do you have internal cable routing or are they external? 7800 has the cables coming put the side and 7900 has them coming out behind the shifter and this enabling them to be wrapped under bars.

    Personally I'd go Tiagra or 105 for value or money. As long as it's 9/10 speed then it won't matter too much. There is a little weight difference but for the extra cash I wouldn't say it's worth going to dura ace level.

    but then Barlist would look a bit of a noob running Tiagra on his Cervelo P3....image

    I'll bite my tongue, shall I? imageimage

  • Ultegra would be fine. Just ride fast. Even faster and 105 would do you.
  • TheEngineer wrote (see)
    fat buddha wrote (see)
    Rocco. wrote (see)
    It will have the number stamped on the shifters underneath the hoods. Easiest way to tell is do you have internal cable routing or are they external? 7800 has the cables coming put the side and 7900 has them coming out behind the shifter and this enabling them to be wrapped under bars.

    Personally I'd go Tiagra or 105 for value or money. As long as it's 9/10 speed then it won't matter too much. There is a little weight difference but for the extra cash I wouldn't say it's worth going to dura ace level.

    but then Barlist would look a bit of a noob running Tiagra on his Cervelo P3....image

    I'll bite my tongue, shall I? imageimage

    I nearly added a few more comments but thought I'd leave others to do so.....image

  • Feel free to add any comments, happy to be corrected on anything image
  • Cheers image

    I think it has to be DA to match the rest of the groupset, yes its bar end shifters so no levers to check.  

    Maybe best I don't mention ive a pair of furry dice hanging from the tribars image



    I had read comments that the 12-27 & 12-28 were not compatible, think I might give Chain Reaction a call tomorrow.


    "The CS-7900 cassette is compatible with the Dura Ace RD-7900 rear derailleur and the RD-7800 rear derailleur except for 11-27 and 11-28 . The RD-7800 rear derailleur does not have ample chain wrap capacity to handle the CS-7900 in 11-27 and 11-28"

     

    http://www.competitivecyclist.com/shimano-dura-ace-cs-7900-cassette

    "The Shimano Dura-Ace CS-7900 Cassette is compatible with the Dura-Ace RD-7900 rear derailleur and the RD-7800 rear derailleur except for 11-27 and 11-28 . The RD-7800 rear derailleur does not have ample chain wrap capacity to handle the CS-7900 in 11-27 and 11-28. These cassettes must be used with the RD-7900. The CS-7900 is optimized for the Dura-Ace CN-7900 chain, but it is compatible with the Dura-Ace CN-7801 chain."

  • Correct Barley -it requires that you have enough range in your rear derailleur cage.

    The sprung motion of the derailleur takes up slack in the chain when you're on smaller gears. As the cage can only swing through a given number of degrees, the longer the cage the more slack it can take up. This allows you to have a wider range of gears. SRAM have the Wi-Fli rear derailleur with a longer cage for this purpose, whilst Shimano have a couple of cage lengths. 

    The 11-27 and 11-28 options have 16 and 17 tooth 'ranges' respectively. Older Dura Ace (7800) simply wasn't designed to accommodate such wide range cassettes. Whilst you can use a 'newer' 7900 cassette, you can't go outside the range offered by the original design. The widest range that will fit, as competitive cyclist states, is the 12-27 (15 tooth difference).

    Now 7800 did give the option of running a compact crankset, which in itself has more range. It's possible therefore that if you're running a standard crankset, you could buy an 11-27 and "get away" with it, but I'd offer no guarantees as there are other geometrical restrictions for rear derailleurs which may well come into play at that point.

  • So it depends if you have 7800 or 7900 rear mech if you want to run a 12-27. I didn't realise the 7800 had a short range. I'm running 12-27 on 7900 no problem.



    To check what rear mech you have the 7800 is a shiny silver chrome look and quite rounded and smooth whilst the 7900 is a dark grey colour and a bit squarer in shape. It should have the number stamped on it for clarification
  • Given when you bought the bike, it's 7800. A 12-27 will fit, but go no wider.

  • i'm running a 12-30 (Ultegra) cassette on a 7900, no problem. (with a 7950 compact chainring too)

    lets be honest.... its all prep for an Ironman on my 100th birthday
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