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Thread: 12-27 vs 12-25

  1. #1
    2011 TCR Advanced SL Spinz's Avatar
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    12-27 vs 12-25

    Is there any benefit going to the 12-27? Will two more teeth make that big a difference when climbing hills? I've the standard Ultegra double chain rings 52/39. Lp

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    Depends how strong and heavy you are. I find that a 27 tooth helps a great deal if I'm climbing a steady, long grade at anything above 6% and a few miles, but I'm 200 lb. Otherwise, a 12-25 suits me just fine for almost all riding. If you are struggling to keep a comfortable cadence on a hill, a 12-27 might be good for you. The added benefit, if you consider it a benefit, is that you can stay in the big ring more of the time (you can do a lot of riding in the 53-25 gear).

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    Senior Member Matt Gaunt's Avatar
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    Do you feel the need for the extra gearing? If not, then probably not. If so, the extra two teeth will help.
    Matt
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    The step from 25 to 27 is 8% which is not insignificant.

    The nice thing about going from a Shimano 9 or 10-speed 12x25 to a 12x27 is that the only changes are in the two largest cogs and all of the other steps remain the same.

    A 12x25 10-speed is 12,13,14,15,16,17,19,21,23,25 while a 12x27 is exactly the same from 12 through 21 and the last two cogs are 24 and 27. There are no compromises in the cogs you use most.

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    As Matt Gaunt has suggested, if you are climbing a lot in your 39-25 and wishing for more gearing, then the 12-27 cassette will be of some use. If you are walking hills now with a 12-25, then most likely a 12-27 isn't going to get you to the top without dismounting. If it's that bad, get a compact crank.

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    Elitist Troglodyte DMF's Avatar
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    Heck with that, go for a triple. When you need it you need it.
    Stupidity got us into this mess - why can't it get us out?

    - Will Rogers

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    2011 TCR Advanced SL Spinz's Avatar
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    Thanks . Lp

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    Senior Member Matt Gaunt's Avatar
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    Quote Originally Posted by DMF View Post
    Heck with that, go for a triple. When you need it you need it.
    Know what, I have no shame riding a triple. It's there when I need it, which is very very rarely these days but I still like having it. Especially on some of the mountain passes in the Lakes back home. 30% is not uncommon and NO fun on a double.
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  9. #9
    slower than you Applehead57's Avatar
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    One thing I've learned, I can climb any single hill, but it's the second, third (etc) hill thereafter that tires me out.
    In upstate NY, the hills are endless, so I run a 11x28 on a triple. I appreciate having the granny gear that lets me keep riding hill after hill after hill. Slow perhaps, but it lets me take the long way home.
    "Lack of opportunity does not constitute virtue". Diana Tickle.

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    I can't tell you how much fun I've had riding the hills around where I live, especially the killers in the last couple of miles to my house, since I went to a triple.

    To OP:like others have said, if you find yourself thinking you wish you had lower gears, go for the 27. There's virtually NO downside. Plus, in the big picture of bike gear, cassettes are relatively cheap unless you go the top end.

    Or you could be wishy washy and go with the SRAM 12-26 8-) But, seriously, if you want lower gears, 25 to 26 would be nearly insignificant, whereas going 27 would be noticable I think.

  11. #11
    Packfodding 3 caloso's Avatar
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    It's definitely noticeable.
    Cyclists of the world, unite! You have nothing to lube but your chains!

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    Commuter bike: 48/38/28 triple with 11/28 cassette
    Road Bike #1: 52/42/30 triple with 12/25 cassette
    Road Bike #2 (lightest of the bunch by a lot): 52/42/30 triple with 12/27 cassette

    Can you tell what kind of crank I prefer?

  13. #13
    Senior Member lighthorse's Avatar
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    There is a benefit with a lower gear. Only you can say whether it is worth the cost to change. I have triples on all of my bikes except the CFR. The other side of this issue is wider spacing between gears. I a perfect world you would only have to change one tooth when you changed gears, thus achieving a smooth thransition every time. When you have lower gearing, then you often have wider spaced gears throughout the cassette. Only you can decide how you like to balance these variables.
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    And one more thing... If you have a lot of stock to take with you, going uphill with the added weight, you will need that 27 gear on the rear.

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