triple to compact double. Easy or not?

1964johnr
1964johnr Posts: 179
edited November 2017 in Road general
I posted a couple of times recently about converting my old square taper triple crankset to a new Hollowtech compact double and switching the BB as well. However, it was pointed out to me that I culd just switch to a square taper compact double at a fraction of the cost. So, that is what I intend to do. I have seen a suitable crankset for £25 at SJS Cycles on line. I am aware that I will need an adjustment to the front mech, but i'm now thinking about other possible issues like not getting an appropriate chain line and maybe my Shimano Tiagra triple front mech might need changing. Could anyone who is an expert on this take a look at the SJS compact square taper double and let me know if I might have any issues? Thanks.
I guess I should have put this on the workshop forum, but I get more replies here.

Comments

  • craker
    craker Posts: 1,739
    Cranksets tend to need recommended axle lengths, I suppose triples are wider and need a longer axle (110mm +) and a single speed is as narrow as can be (103mm or so). So yes, you may find your new crank sticks out more than it ought to, you may be able to live with that?

    Square taper BBs are pretty cheap (from £5 but get one worth fitting), if you haven't got the tools that will cost you extra.

    I wouldn't necessarily recommend the cheapest double crank you can find, it'll likely shift lousily compared to your Tiagra. It may be for a 7 or 8 speed chain, though you'd probably be OK on a 9 speed chain. And I've done similar (on a Tiagra triple front mech and shifter) works fine with a double setup.
  • W631
    W631 Posts: 7
    I did triple to compact this way - 32t inner ring,48t on middle ring,outer ring vacant,11-32t cassette.That way you don't have to change anything.BB,front and rear mech,brifters,chainset are all the same.
  • Moonbiker
    Moonbiker Posts: 1,706
    good idea ^

    outer ring you could just have a bash guard.

    also compacts are different bcd so need different rings incast you were unaware
  • Bumo_b
    Bumo_b Posts: 211
    From my recent experience, the crank lengeths on the hollowtechs are identical, although the triple requires a spacer. Apart from that it was just a lower limit screw that needing adjusting.
  • 1964johnr
    1964johnr Posts: 179
    I like the idea of just removing the biggest ring of my triple completely and replacing the middle ring with a larger one than is there at present, perhaps 48 teeth. However, how do I determine which chainring to purchase. I know it will need to be a five hole ring, but I think I need to calculate BCD measurements - not sure how I do that, and at present my middle ring and outer ring are connected to the spider at the same points, so If I only want one ring connected, will my current chainring bolts still work? Any help with this would be appreciated.
  • W631
    W631 Posts: 7
    1964johnr wrote:
    I like the idea of just removing the biggest ring of my triple completely and replacing the middle ring with a larger one than is there at present, perhaps 48 teeth. However, how do I determine which chainring to purchase. I know it will need to be a five hole ring, but I think I need to calculate BCD measurements - not sure how I do that, and at present my middle ring and outer ring are connected to the spider at the same points, so If I only want one ring connected, will my current chainring bolts still work? Any help with this would be appreciated.

    Compact bcd for my Stronglight is 110mm for outer and middle rings and 74mm for inner ring.You will probably.need new chainring bolts. i.e.for a single ring.Try the existing bolts first.

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