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  1. #1
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    Double v. Triple Cranks?

    I recently realized that some people are running double cranks instead of the standard 3 that come on many bikes. Does anyone have a good source for information as to the advantages of double cranks? Does converting to double require a new front derailer and/or rear cassette as well?

  2. #2
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    Some advantages of a double are better chain line, lighter, and you can also use a bash ring in place of the outer ring with higher clearance compared to a triple. Advantages of a triple are the ability to use a low granny gear, a good middle ring choice for your application, and a high gear of your choosing. It all depends on what you do with your bike.

    I had a 24-36 with bash ring which was actually a very nice combination on my Pugsley, but went to a Phil square taper and Middleburns 20,30,40. This combo gives me 17- 84 gear inches ( 14-34 rear ) and I have many more gear options. I don't need anything more than 84 G.I. with my Pugs. It's all personal choice. The only way you'll know what's best for you is to try and see.

  3. #3
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    Some of your answers are here click here

    I don't necessarily agree about the chainline being better. A 3x9 has a lot of gear overlap so of you can potential obtain a better chainline after doing a lot of shifting. Aside from that I prefer 2x9
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  4. #4
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    Quote Originally Posted by 1-bar
    Some of your answers are here click here

    I don't necessarily agree about the chainline being better. A 3x9 has a lot of gear overlap so of you can potential obtain a better chainline after doing a lot of shifting. Aside from that I prefer 2x9
    True but some of that overlap (and resulting better chainline) is theoretic. In real world application you're not going to be dropping from the middle ring to the granny while bumping up two on the cassette, then back up to the middle with one down on the cassette... all in search of that right gear - and optimal chainline

    I think the reality is that you work your way 1/2 to 2/3 the way up or down the cassette before moving from one chainring to another.
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  5. #5
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    Quote Originally Posted by OldZaskar
    In real world application you're not going to be dropping from the middle ring to the granny while bumping up two on the cassette, then back up to the middle with one down on the cassette... all in search of that right gear - and optimal chainline.
    This is exactly what I do 100% of the time... I always shift rear when changing front to compensate for the big gap... anyone who thinks of chainline while riding needs a more technical trail...
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  6. #6
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    I've only recently understood the concept of shifting both derailleurs together to find the right gear, and also to stay in an acceptable chainline. They both go hand in hand. Choose the right gear combo, and your chainline will be good. I hardly used my granny with my double, so never had to shift the front.

    Now with my triple, I've worked out a formula in gear inches where I have optimum gearing and good chainline going from granny to middle to big and down again. I've got Sram XO twistshifters, which operate on a continuum, so easy to crank up or down changing multiple gears in one stroke. The green numbers are my optimum gears, and it's easy to switch both derailleurs simultaneously to stay in the green.
    Attached Thumbnails Attached Thumbnails Double v. Triple Cranks?-dscf1442.jpg  


  7. #7
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    There are 2 separate 2x9's as described. One is the 'technical trail' 2x9, which is outer ring replaced with a bashguard.The other is a 'racer' 2x9 (or 10 nowdays), and the rider is either stronger or liver in flatter areas. the 3-ring crank is ofter replaced with a dedicated 2-ring unit with a ratio like 44/29 (for flat) or 40/27. You lose a ratio or two from a 22T granny, even with a cassette like SRAM's 11-36. It is most commonly used by racers as there is a weight advantage, and it is more efficient shifting-wise to be able to stay in the large ring for longer.
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  8. #8
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    Quote Originally Posted by suba
    I've only recently understood the concept of shifting both derailleurs together to find the right gear, and also to stay in an acceptable chainline. They both go hand in hand. Choose the right gear combo, and your chainline will be good. I hardly used my granny with my double, so never had to shift the front.

    Now with my triple, I've worked out a formula in gear inches where I have optimum gearing and good chainline going from granny to middle to big and down again. I've got Sram XO twistshifters, which operate on a continuum, so easy to crank up or down changing multiple gears in one stroke. The green numbers are my optimum gears, and it's easy to switch both derailleurs simultaneously to stay in the green.
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  9. #9
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    I should've been clearer - Yes, when you drop from the front ring, you'll most likely come up a couple in the back. But beyond that, you're not going to be going back and forth - with the front, e.g. once there, you work those 5-6 cogs then move the front ring and do it all again
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  10. #10
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    How much gear range do you actually lose with the double cranks? Are the two gear sizes that you have different so that you lose range?

  11. #11
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    Quote Originally Posted by RobDMB
    How much gear range do you actually lose with the double cranks?
    The gear-calculator on the following page will help answer that question:

    http://www.sheldonbrown.com/gears/

    On my bike, when I replaced the 44-tooth ring with a bashguard, I lost only two ratios. Only two. Hardly worth quibbling about, especially as they were at the high-end that I never reach anyway when I'm on the trails.

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    Honestly I'm not really sure how to interpret that chart. I have a Giant Trance 1 and the specs list it as having RaceFace Evolve XC, 22/32/44 Cranks and a SRAM PG980 11-34T, 9-speed Cassette.

    I was considering replacing the cranks with the Shimano SLX Double - which I believe is 36-22T. Could anyone help me interpret how much I would lose?

  13. #13
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    You can work the math yourself easily enough. Let's take the 44-tooth chainring and the three smallest cogs:

    44/11=4
    44/13=3.4
    44/15=2.9

    Then compare with the same cogs and a 36-tooth ring:

    36/11=3.3
    36/13=2.8
    36/15=2.4

    I would call 3.3 "close enough" to 3.4, so at the high end you lose only one gear ratio by giving up your 44 tooth ring in favor of a 36-tooth middle.

    Now you may lose a ratio or two elsewhere, but in my mind what matters are how high you can go and how low you can go. So long as the ratios in between are reasonably spread out, I don't obsess too much about them. A 44-tooth ring lets you go only one ratio higher than does a 36-tooth. Meh. Who cares about that.

    BTW, that SLX double crankset rocks. I run two of them, and like them so much I bought a third just to have on hand as a spare.

  14. #14
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    Thanks for the explanation. One more newb question - does the lower number (i.e. ratio) mean it is easier to pedal or does that indicate a higher gear meaning its harder to pedal?

  15. #15
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    Rob, given the order in which I did the division, yes, the lower number means easier to pedal.

    For example:

    44/13 is easier than 44/11
    3.4 is less than 4

    I suppose one could choose to reverse the math, as in 11/44 and 13/44. So long as you are consistent, it really doesn't matter.

  16. #16
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    Thanks - - in general - besides the double v. triple distinction - is the Shimano SLX crank and upgrade/downgrade/equal to a Raceface Evolve XC crankset?

  17. #17
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    I like to think in terms of gear inches. Gear inches are the amount of linear inches your bike will travel with one revolution of the peddles. You have 26" wheels, so the following are your g.i.

    The green numbers are what I feel are your usable range for a good chainline. You can see with the 22-36 combo you have 14 optimum gears imo. With the 22-32-44 you have 19 useable gears with a top gear of 104 g.i. ( if you can push it ) but the real difference imho is that you have a 32 which gives you lower gearing for the middle gear compared to the 36, and you can also switch to the 44 to give an edge ( 19 more inches of travel per revolution ) on the high end compared to the 36. I hope this helps, and would be happy to explain further if you wanted.
    Attached Thumbnails Attached Thumbnails Double v. Triple Cranks?-dscf1448.jpg  

    Last edited by suba; 03-11-2010 at 08:27 AM.

  18. #18
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    Quote Originally Posted by RobDMB
    Thanks - - in general - besides the double v. triple distinction - is the Shimano SLX crank and upgrade/downgrade/equal to a Raceface Evolve XC crankset?
    That I honestly don't know. I don't really have any personal experience with Raceface cranks, at least not enough to mention.

  19. #19
    r29
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    Bump.

    Could someone explain how this works still confused new to riding.

    cassette SRAM PG830 11-28, 8-speed
    chain KMC Z72
    cranks TruVative ISO Flow 3.0, 22/32/42
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    hubs Formula 32H Disc
    spokes Stainless Steel
    tires Kenda Nevegal 26 x 2.1"
    Giant Yukon FX

  20. #20
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    r29, what exactly do you want to know?

  21. #21
    r29
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    switching from triple to double.

    What would i gain or lose in ratio i guess.

  22. #22
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    You would normally lose slightly, but not nearly as much as you might think. The easy way to try switching is to replace your 44-tooth ring with a bashguard. Then adjust your front derailer stop so as not to shift into guard. Viola! You have 2x9.

    When I converted my own bike from 22/32/44 to 22/32/bash, I did the math and found that I lost only two ratios at the high-end. You'd think you'd lose nine ratios, but there is so much overlap that you really lose only a couple.

    Right now, my mountain-bike is configured 22/32/bash. I don't miss the higher ratios, because I'm just not that fast in the woods.

  23. #23
    r29
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    well i got 22/32/42/bashguard
    truvactiv isoflow 3.0

    so if i was to remove the 42 what would i lose?

  24. #24
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    Quote Originally Posted by r29
    well i got 22/32/42/bashguard
    truvactiv isoflow 3.0

    so if i was to remove the 42 what would i lose?
    you would lose a 42T ring

    Seriously, just ride around and not use it and see what it's like
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  25. #25
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    So many of us including myself forget the blessing we have living in the States. We ponder what bike components will suit us best, while half of the world ponders how they will eat today, and how will they survive tomorrow.

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