Converting from 3 to 2 chainrings

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  • Converting from 3 to 2 chainrings
  • rocketman
    Member

    …seems to make sense that the middle of the cassette should align directly between the two chainrings

    The chainline is fine as it is.

    Granny ring lines up with the largest cogs on the cassette, middle ring lines up with the middle of the cassette.

    MarkiMark
    Member

    Thanks Rocketman, but I’m still a bit concerned that the chainline will be crap in faster gears. Anyone else ever thought this is a problem. Probably just me then….

    IMO you want the larger ring in line with the middle of the cassette so that you get the max number of gears from it without screwing up the chain line. I can get all 9 cogs on my 36 ring on a 2×9 setup, but normally try to restrict it to the smallest 7

    perthmtb
    Member

    +1 for it not being an issue. FYI the Shimano SLX double & bash has its two rings in exactly the same place as the middle and granny on the SLX triple, so they obviously didn’t think it was a problem.

    I run a triple converted to double & bash on one of my bikes, haven’t altered the chainline from when it was a triple, and get all 18 gears without any rubbing/chain drop issues. We’re only talking a couple of mm here, so if your chainline is reasonable to start with, it shouldn’t be a problem.

    andyl
    Member

    If you have a spacer on the non-drive side of the BB then you could move it over to the drive side to get a slightly better chain line if using the granny middle. But it’s not that important, tbh the biggest problem using the 11T sprocket on the middle on a triple set up is the risk of catching the chain on the edge of the big ring.

    If using the middle and large rings and ditching the granny then you could shift a spacer to two from the drive side to the non-drive side.

    I wouldn’t space any chainrings out as it reduces the strength of the attachment and you need to keep the spacing between the rings the same.

    MarkiMark
    Member

    Can anybody answer this, I’ve looked at a few sources but they don’t address this specific question…

    With a 3 ring setup the middle ring is aligned with the middle of the cassette for the most effective chainline. I want to convert to a 2 ring setup and it seems to make sense that the middle of the cassette should align directly between the two chainrings. This means that simply removing either the outer or inner chainring will result in a chainline that doesn’t achieve this.

    Initially I thought I could just remove a bb spacer (x-type) but x-type axles are generally fixed length so this approach doesn’t work. If it helps, I’m running a Race Face Deus XC chainset with 104 bolt circle diameter.

    Has anybody done this? Are there special chainring bolts that act as a spacer?

    Any help appreciated.

    MarkiMark

    MarkiMark
    Member

    Thanks to all. I’ll stop my worrying now and get a good night’s sleep.

    MarkiMark
    Member

    Sorry, one more thing….

    If I do go 2 rings, what sizes do you find work best. I’m guessing maybe a 36 and a 24/26. I rarely use my 22 and 34 combination anyway at the moment.

    Premier Icon Speshpaul
    Subscriber

    I’m running 32/22 and 32 at the rear for the time being, as its what i had and i’ll probably figure out what a need after a few weeks of riding. But as i’ve only used the 32 up front so far i might ditch the 22 until the rainy season.

    nosedive
    Member

    I’ve got 36 \ 22. It gives a great spread of gears but you can end up spinning legs comically when dropping from the big to the small ring

    I run 36/22 with an 11/36 cassette and I do use the lowest gears a lot partly because of the local terrain and partly because I’m an old git.

    If you don’t need that low gearing go for 38/26 or 40/28

    perthmtb
    Member

    At the risk of stating the obvious, everyone’s gear requirements will differ – it depends on your fitness and where you ride, and whether the bike is a 26 or 29er, so I’d suggest asking what others ride isn’t a very good way of choosing what’s right for you.

    Better to work out your own ratios using a gear calculator like this one Sheldon’s Gear Calculator where you can pick what your top and bottom gears will be, and how much overlap you want.

    Things to watch out for – a bigger difference in teeth between your front rings will give you a greater range, and less overlap, but go too far and shifting starts to get a bit clunky. My experience has been that a 10T difference (like 22/32) will be smooth as, a 12T difference is still fine, but by a 14T difference it’s starting to get a bit clunky (unless you have specifically designed rings and FD like the SLX M665).

    My experience has been that a 10T difference (like 22/32) will be smooth as, a 12T difference is still fine, but by a 14T difference it’s starting to get a bit clunky (unless you have specifically designed rings and FD like the SLX M665).

    Not sure I agree with that. I do have an SLX 22/36 double and bash. but still use the original XT triple front mech that came with the bike. The shift is fine but needs slightly more shove and a fraction extra time. The offset is that I’m changing front ring far less often than with a triple so it’s just not a problem

    perthmtb
    Member

    Just basing it on my experience – tried cobbling together a double by using ‘normal’ 22 and 36 rings and a triple mech, and had all sorts of issues – clunky shifts, chain drop, chain rubbing on inside of 36T ring. Changed to the SLX M665 rings and FD and peace and quiet was restored. Can’t honestly say whether it was due to the different rings or the double specific FD, but suspect it was a combination of both…

    stanfree
    Member

    Im going to do the exact opposite and go from 2 to 3 chainrings. I’ve recently put on a new cassette and chain so had measured the chain round the 2 big rings (not through the rear mech).

    So am I right in saying I will need to add links , adjust high limit screw anti clockwise and then fine tune back clockwise to stop it jumping off the outside chainring. ?

    Sorry to the OP for highjacking the thread.

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