Comparing Granny Gears- Mtbr.com
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  1. #1
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    Comparing Granny Gears

    The granny gear on both these bikes is 1.5 ratio for the SRAM 2x10 and 1.4 ratio for the XCT 22/32/42, right? About a 7% difference, which is not much, right? Using the sheldon brown program Sheldon Brown's Bicycle Gear Calculator Thanks Bill



    Cranks SR Suntour XCT 22/32/42t
    F. Derailleur Shimano TX50 dual pull, Top swing, 34.9
    R. Derailleur SRAM X-4 8spd
    Shifter SRAM X-4 trigger 8spd
    Gear SRAM PG-820 8spd Cassette (11-32t)


    SRAM X7, 2x10 Speed
    Front Derailleur SRAM X7
    Rear Derailleur SRAM X9
    Cassette SRAM PG 1050 11x36, 10-Speed
    Chain SRAM PC 1051
    Crankset SRAM X7, 26/39

  2. #2
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    Sounds like ~7% difference if your ratios are correct, not a huge difference, but you might feel it on a steep climb, probably about half a gear on the big end. For example between the 36 and 32 teeth cogs on the 11-36 cassette is a 12.5% jump.

    I'm more a fan of gear-inches myself that gear ratio, but you come out the same basic information in the end.
    Last edited by 4Crawler; 05-24-2012 at 12:40 PM.

  3. #3
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    Typically 8 speeds have ~ 13% change in ratios between gears.
    A 9 speed has ~12.5%, mainly just one more gear than 8 spd.
    A 10 speed has ~12.3% , again mainly just one more gear than 9 spd.
    So a 7% change is more or less 1/2 gear change, or, not much.

    My original setup had a granny gear 1.455 and 2nd gear of 1.182, a 19% change - a kind of large change. I swapped cartridges so the change from granny to the next gear is 13% and found the result an improvement.

    If you look at all the cassettes/crank combinations generally the change from gear to gear is around 13% so they must have discovered that's a useful ratio - significantly lower % is a worthless spliltting of hairs, significantly great % can be uncomfortable.

  4. #4
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    Thanks, 7% is ok, maybe better.

    Can someone check my calculations with the program? I think I enter the numbers correctly?

    Thanks
    Bill

  5. #5
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    Quote Originally Posted by Billinsd View Post
    Thanks, 7% is ok, maybe better.

    Can someone check my calculations with the program? I think I enter the numbers correctly?

    Thanks
    Bill
    Looks like your calculation for the 8 speed granny is off. I got 1.3 for granny on the 3x8, which makes more sense.


  6. #6
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    I checked again and got 1.5 for the 8 speed and 1.6 for the 10 speed. I am using 29 inch wheels also. Thanks Bill

  7. #7
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    Is that ratio on 10-speed 26/39 front 11-36 rear the same as 9-speed 20/32 front 11-34 rear?
    "This is a male-dominated forum... there will be lots of Testosterone sword-shaming here" ~ Kenfucius

  8. #8
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    Quote Originally Posted by Zachariah View Post
    Is that ratio on 10-speed 26/39 front 11-36 rear the same as 9-speed 20/32 front 11-34 rear?
    Nope, the 9 speed is quite a bit lower. My ratios are not the same as Sheldon's because his take into account crank length and tire circumferance which I don't. Anyway, by my basic calculations:
    10 speed granny = 1.385
    9 speed granny = 1.70
    The 26 tooth small gear on front must be for a 26" tire and a bit large at that, mine is 22/32/44 and the 20 tooth for the 9 speed is more likely for a 29" (I assume in so far as I don't have a 29"). It would be quite low for a 26", in fact too low because there comes a point where you have to maintain a fast cadence while creeping up a steep hill which for me is a formula for wiping out my legs real quick and not maintaining very good stability in the process, AKA a 1 mph "wipe-out."

  9. #9
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    his take into account crank length and tire circumferance which I don't
    Why not? Somebody once told me if you are going to do something, you might as well do it right. Difference is usually only 10-20%.

  10. #10
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    Quote Originally Posted by Yogii View Post
    Why not? Somebody once told me if you are going to do something, you might as well do it right. Difference is usually only 10-20%.
    Cuz I have only one bike, one crank, one brain cell working on this, (the other one's resting) and I know if I go to a smaller tire (e.g. 1.95) the ratio will be a bit higher, and my math was easier than his. It's all relative.

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