Shimano GRX 600 series cranks on 'regular' bike

secretsam
secretsam Posts: 5,098

Hi all, am thinking about lowering my gears by using GRX double chainset with 46/30 rings - would this work on a road bike with either 6800 105 or 8000 Ultegra? I seem to recall there was something odd about the spacing on GRX doubles


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Comments

  • Wheelspinner
    Wheelspinner Posts: 6,562

    Dunno about the spacing although I'd be surprised if that was a problem - 11 Spd has fairly standard parameters. The one issue you might find though is whether your road frame will allow the front derailleur to be mounted low enough to suit.

    If you have a braze on type, the bracket may not extend far enough down the seat tube to reach (mine wouldn't on a Cervelo - it's at the lowest limit for a 50/34 combo).

    If it's a clamp band, just check it sits correctly on the seat tube.

    Open One+ BMC TE29 Seven 622SL On One Scandal Cervelo RS
  • whyamihere
    whyamihere Posts: 7,702

    It might work. The chainline is 3.5mm wider, so if you have enough travel left on the limit screws that could be ok, but it's quite a large adjustment. It's going to need to sit lower as well which your frame may not accommodate. The GRX front derailleur is only about £30 though and is compatible with road levers, so I'd probably save the hassle and just fit that as well.

  • daniel_b
    daniel_b Posts: 11,580
    edited January 4

    I'd like to add a vote for the GRX800 48/31 - really great range of gears out on the road.


    £135 at Merlin currently.

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  • I did this last summer and about 2000 miles ago on my Pinnacle Dolomite. I swapped out a 105 7000 compact for a GRX double (can't remember off the top of my head whether a 600 or 800 series) with no issues and I even got away with not dropping the front mech down any lower (it's a band on so I could if needed) and no issues on shifting on the front rings. Chain line etc all looks the same

    Really enjoying the lower gears as well to be honest. Not yet spun out and find it less tiring to ride. Use more of the cassette as well so where is more even

  • dj58
    dj58 Posts: 2,217

    I tried this on a 2013 Giant Defy O.E. FC6750 50/34, FD5700 105, RD6700-A and CS4600 12-30T. As eluded to above, if your bikes have a braze-on front derailleur moving it down to Shimano's recommended distance of 1-3mm from the top of the 48T/46T chainring may not be possible.

    In my case it was this along with the FD5700 105, which is not compatible with a 48T/46T chainring and the extra 3.5mm chainline that caused the GRX400 crankset to not work. I do think that if I swop the FD5700 105 for a FD4700 Tiagra and use a TCX compact braze-on FD bracket I could get it to work. You have FD6800 and FD8000 on you bikes so you might have more success.

  • secretsam
    secretsam Posts: 5,098

    LOL I have a Dolomite as well, that's what I'm proposing changing it on! Having said that, I've bought an 11-34 cassette and long-cage 105, so I can get a 1:1 fitted. I was more thinking if I did an E2E it might be useful to have super low gears...plus I might put the 11-34 on my road bike (currently 11-32).


    It's just a hill. Get over it.