Converting 26/38 Shimano XT Crankset to 26/40?

Discussion in 'The Workshop' started by Waldo, Feb 11, 2014.

  1. Waldo

    Waldo Lebowski Urban Achiever

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    A couple months ago I got a Giant Anthem 29er, which has a full XT group including a long-cage rear derailleur (non-Shadow), 11/36 cassette, and a 26/38 crankset. The lower climbing gears work well for me, but I'm finding myself pedaling around on the big ring a lot and I'm spun out at around 24-25 mph, so I keep wishing for more top speed.

    So the question is: Can I swap the 38t big ring for a 40t, or is that too big a jump for the front derailleur to shift well? (Or is there such thing as a 10-36 mtb cassette?)
    I've dug around the interwebs and asked one or two folks in bike shops, but I keep getting different answers. Can anyone point me to a definitive source on this, or better yet, have any of you actually done this exact change?

    Thanks in advance for your input!
     
  2. me and my bike

    me and my bike New Member

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  3. Waldo

    Waldo Lebowski Urban Achiever

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    That's one of the areas of confusion that has me hoping to find someone who's actually done this switch. I've read about their different letter codes, but have seen some comments that mixing between the series will still work, though maybe not as smoothly as with perfectly matched rings.

    :?:
     
  4. me and my bike

    me and my bike New Member

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    When i spoke to shimmano they told me that it wasnt going to be crisp or clean shifting, though they also didnt know the defintie answer. Id stick to keeping them the same, or even look into replacing the rings with another companys rings such as blacksphie or raceface which dont use the complicated system
     
  5. bvader

    bvader Long Live The Gorn!

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    My experience 14 tooth jump is not going to be great....I tried 22/36 didn't work very well... you are really going to need to unload the pedals.
     
  6. mfoga

    mfoga Intense Whore

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    I think it would depend on the FD. Shimano sells 38-24 cranksets now but having one I can say going from little to big is not perfect and have slight issues occasionally. Most the time I just have down again and then up again.

    I would say the 40-26 would work the same.
     
  7. me and my bike

    me and my bike New Member

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  8. duke777

    duke777 Active Member

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    Shimano FDs are designed to have the 12 teeth difference between rings, this also means the cage's high and low point will be off if you deviate from the 14 teeth difference between rings. Most likely you will have some issues getting the lower front ring to work with smallest cog once you get the big ring dialed in, but that's probably not an issue for you since you are looking for a bigger big ring. 24/38 is a bit of exception since the lower ring would be low enough in relation to the rear cassette where the 14t difference is possible.

    Another alternative is SRAM's FD since they support 26/39 combo the FD might work better if you run into issues with the shimano FD. But I doubt you'll have any real issues.
     
  9. dcrfx

    dcrfx Member

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    There is such an option for the rear cassette, Shimano's Capreo system (microdrive). I saw it on Canfield Brothers website, get's you a 9-36 10 speed cassette range. Unfortunately, you have to have a Capreo sized free hub to fit the tiny 9 and 10 tooth cogs (so you have to have your rear wheel build up with a microdrive hub). Canfield sells a microdrive hub that looks pretty nice. Shimano sells a Capreo hub but I think it is non-disc only.

    Probably not an option due to the expense of a new hub and wheel build, but thought I'd mention that the small cog option does exist. Link to Canfield info: http://canfieldbrothers.com/components/9-tooth-rear-hub
     
  10. Bplus

    Bplus New Member

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    What duke, said 2x10 shimano needs to have that 12 tooth gap to work most effectively. I'm running the 28/40 and love it!

    Sent from my SGH-T959V using Tapatalk 2
     
  11. mfoga

    mfoga Intense Whore

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  12. Varaxis

    Varaxis Trail Ninja

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    This is the best response, so far. The reason behind chainrings being matched, is due to the "timing" of when the teeth align in a certain way to fit in shift ramps, gates, pins, and specially shaped teeth that allow the chain to smoothly catch, at the ideal points in the pedal stroke. The pins and gates are placed and shaped to catch a specific part of the chain, such as the fat part of the plate by the pin, or the nook of the plate between the chain's pins. Think about it, if you use a smaller chainring, the teeth might be a few mm back and lower, so when the FD pushes the chain up, maybe the inner plate hits a spot that was designed to catch and guide an outer plate. Also, because not everyone spins perfect circles, so Shimano (or any other chainring maker) may design the ramps to be just before and just after when your cranks are in the 3 and 9 o'clock position. This is for the optimum shifting performance. You can run it, but you should at least expect noisier shifts, a delay or reluctance to shift, and a number of other issues.
     
  13. mfoga

    mfoga Intense Whore

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    If you look at the way the matching goes AM is 38/24 AK is 38/26 and AJ is 40/28. So you can't deviate from the Shimano ratios and keep the correct ratio.

    That being said I did use a Sram 24 with the 38 I had on a previous bike and it worked just as good as the Shimano factory 38/24 setup.
     
  14. jeffj

    jeffj Bloated Mountain B'hiker

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  15. Waldo

    Waldo Lebowski Urban Achiever

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    Thanks for all the great info! It was especially illuminating to see that the new Shimano front derailleurs are made for a 14-tooth jump, though it's interesting that they don't spec a crankset with that spread. I'll have to check my bike to see if I have that type of derailleur, and if so, maybe I'll look into trying a matched set of 26/40 chainrings.

    BTW: Someone mentioned going with Shimano's 28/40 rings, but I'd rather not give up the low-end climbing ability of the 26-tooth small ring.

    DCRFX - bonus points to you for the info on the Canfield 9/36 cassette. It hadn't clicked for me that dropping below 11t would mean a smaller diameter freehub. Oops!
     
  16. mfoga

    mfoga Intense Whore

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    They do spec a crankset with that spread. They make a 38/24. I have one on my new Trance. They have three XT 2x cranksets 38/24, 38/26 ad 40/28. I think the its fact that there would be the need to make another set of matched rings to make a 40/26 and not enough demand. They only added the 38/24 last year I think as there was a lot of people asking for a smaller ring.
     
  17. dstepper

    dstepper Over the hill

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    Why not just put a triple on there...triples are cheap now that all the cools kid ride 1x10 and 1x11.

    Dean
     
  18. herzalot

    herzalot Well-Known Member

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    Waldo - stop going so fast and you won't have that problem! If you're spinning out of 38x11 on knobby tires, you're going downhill. Tuck and enjoy!

    If you are truly running out of gears that often, you will have to change your signature. :wave:
     
  19. Waldo

    Waldo Lebowski Urban Achiever

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    I'd much rather pay for one or two chainrings than a whole new crankset.

    Oops - umm, yeah, I knew that ;)

    I'm pretty surprised how often I'm wishing for a little more. Maybe it's just because I've been doing so many fire road rides lately in preparation for that evil event on 4/5, but I can think of a handful of routes where I max out the gears on very slight downhills. I've picked up the pace a bit since we rode together, but many others still go faster on those segments, so I my signature is still plenty accurate (especially on Luge!)
     
  20. MickyMic

    MickyMic New Member

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    I am refreshing this from the darkness of 2014 ;)

    Just 100 km after changing chainring 26T to 22T in 36/26 Shimano M8000-2 crankset. I replaced 26T BC (from 2x11) with 22T BA (from 3x11 22-30-40). Works perfect, I did not notice any problems:)
     

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