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Shimano FC-M770 to Double Crank?

jerryfuddjerryfudd Posts: 343
edited August 2013 in MTB workshop & tech
Hi,

Can anyone give me some pointers on taking a FC-M770 to a double still using XT chainrings? ideally a 26/38? ...or 22/36?

thanks,

Dan
2013 Cotic Bfe

Posts

  • Chunkers1980Chunkers1980 Posts: 8,035
    Ditch the big ring and fit the rings? XT touring comes in 38 middle, any granny of the correct BCD should work. Keep it to 14 teeth difference though.
  • jerryfuddjerryfudd Posts: 343
    Chunkers1980 wrote:
    Ditch the big ring and fit the rings? XT touring comes in 38 middle, any granny of the correct BCD should work. Keep it to 14 teeth difference though.

    Any links for that chainring or model number of the XT touring? so you think 24/38? anything info on a 24T?

    thanks,

    Dan
    2013 Cotic Bfe
  • The RookieThe Rookie Posts: 27,804
    Have you tried looking? The good lord (and this forum) helps those who helpthemsleves.
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • cooldadcooldad Posts: 32,599
    Please use capitals when you refer to me. Or I'll fry your censored .
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • The RookieThe Rookie Posts: 27,804
    CD, just to help you out, the Dr said you were impotent not omnipotent.......
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • cooldadcooldad Posts: 32,599
    I always get those two confused.
    As you were.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • jerryfuddjerryfudd Posts: 343
    The Beginner wrote:
    Have you tried looking? The good lord (and this forum) helps those who helpthemsleves.

    wise words.... I came to the assumption that the tourer was the FC-M771 but middle ring was 36T so wasnt sure if i had it right however would let me keep my 22T granny.... would 2T less really make a difference?

    Dan
    2013 Cotic Bfe
  • The RookieThe Rookie Posts: 27,804
    36-38T equates to about 1/2 gear at the rear, only you can say if you need the extra top speed capability or not!
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • jerryfuddjerryfudd Posts: 343
    The Beginner wrote:
    36-38T equates to about 1/2 gear at the rear, only you can say if you need the extra top speed capability or not!

    thanks :)

    Dan
    2013 Cotic Bfe
  • bubbachunksbubbachunks Posts: 5
    Sorry to jump in on post hope dont mind am after a doublering setup advise. I have a xt770 9 speed 3x9 setup and would like to try a 2x9 setup and thinking of 24/36 or 22/36 up front and am looking at blackspire or middleburn rings but have read on certain cranksets of rings not working and wondered if anyone knew also if could adjust limit screws and still use the 3 speed trigger shifter to try this setup or any advise or links for chainrings hope you can help many thanks
  • njee20njee20 Posts: 9,613
    Those rings will be fine on that crank, at worst you may need to file the ring slightly to fit.

    You can just adjust the limit screws and use the same shifter.
  • Chunkers1980Chunkers1980 Posts: 8,035
    Yes, but why? You already have a 22/32/44 setup.
  • njee20njee20 Posts: 9,613
    Why not? I've not used a triple for about 7 years now, and wouldn't go back. Converted all my chainsets to doubles until they became more common a couple of years ago.
  • Chunkers1980Chunkers1980 Posts: 8,035
    Because for the sake of a couple of links of chain and the ring's weight (a tad if ground clearance) I lose the range of gears I actually use.
  • njee20njee20 Posts: 9,613
    Good for you, the OP may well be different, I know I am. No use for a 22t whatsoever, and a 44t is just a little tall, so why not go somewhere in the middle? It gives 2 more usable rings, allowing you to use the entire cassette in either, with the added bonus of reduced drive train wear from and lighter weight.
  • Chunkers1980Chunkers1980 Posts: 8,035
    Which is why I asked, why!
  • njee20njee20 Posts: 9,613
    Fair enough! There's your answer!
  • bubbachunksbubbachunks Posts: 5
    just fancy trying it so as people say is great so thought would give a go thanks for the help will let you know p.s is there any rings you would advise eg middleburn etc
  • badhopperbadhopper Posts: 8
    bubba, I've done the same thing (3x9 to 2x9), keep your 22t granny ring and buy a 36t steel shimano deore middle ring and buy some single ring chain ring bolts. Works real good I have no regrets.
  • jerryfuddjerryfudd Posts: 343
    badhopper wrote:
    bubba, I've done the same thing (3x9 to 2x9), keep your 22t granny ring and buy a 36t steel shimano deore middle ring and buy some single ring chain ring bolts. Works real good I have no regrets.

    was looking at doing the conversion but unless as you say replace the middle with a 36T there seemed little point as you might aswell just not shift into the 44T and have the same result? ...decided in the end that would only be worth it if I was going to go 2x10 or even 1x11 would be interesting if it would be possible depending on the range.

    Dan
    2013 Cotic Bfe
  • bubbachunksbubbachunks Posts: 5
    Did you have any trouble eg chain rub and did you just adjust limit screws etc glad you like it the more people i speak to the better it sounds many thanks
  • badhopperbadhopper Posts: 8
    Yes, just adjust the limit screw so you can't shift up past the middle chain ring.

    I also slid the front mech down the seat tube a bit, giving the same clearance to the new middle ring as it had on the old outer ring.

    You will also want to shorten your chain to suit.
  • bubbachunksbubbachunks Posts: 5
    Did you fit it and adjust the stops and all works with no issues at all, was looking at a blackspire pro as wanted a nice looking one, sad I know but if the steel works fine would be very tempted have you a picture you could post
  • jerryfuddjerryfudd Posts: 343
    I saw this which looked a nice setup with a RaceFace bash....

    361ACE8F-5F9B-4686-BA2F-C1A3B1A560BB-2821-0000015F1FB9D7CF_zpsc71dcc51.jpg?t=1375783750

    Dan
    2013 Cotic Bfe
  • badhopperbadhopper Posts: 8
    20130807_171219_zpsf3a9fb2d.jpg

    I chose a steel chainring because it will be more durable.

    The chain shifts from 22 to 36 and back fine.

    Shimano chainrings have a notch that you align with the drive side crankarm so they work together and aid chain shifting.
  • bubbachunksbubbachunks Posts: 5
    Just a quick update fitted a blackspire pro chainring and works lovely with minimal rub on extreme gears but might have to put a 24t on the inner cheers for all the help
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