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  1. #1
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    Rohloff Gear Spacing

    Hi

    I am currently in the middle of purchasing a Rohloff Speedhub to fit to my Uzzi VPX (amongst others, as I'm hoping to be abel to chang eit form bike to bike), I am wondering how I'd go about making the gear spacing perfect.

    Currently I run a XTR 22/34T cassette and this gives the perfect spread of gears with my 36T/24T dual ring.

    I've been told to run a 38T chain ring and a 16T sprocket to get the right gearing, does this sound about right to you?

    Also do you know who makes a 38T outer ring? I currently have a Race Face Atlas Crank which I want to keep...
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  2. #2
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    Reputation: Monte's Avatar
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    Quote Originally Posted by Transition J
    Hi

    I am currently in the middle of purchasing a Rohloff Speedhub to fit to my Uzzi VPX (amongst others, as I'm hoping to be abel to chang eit form bike to bike), I am wondering how I'd go about making the gear spacing perfect.

    Currently I run a XTR 22/34T cassette and this gives the perfect spread of gears with my 36T/24T dual ring.

    I've been told to run a 38T chain ring and a 16T sprocket to get the right gearing, does this sound about right to you?

    Also do you know who makes a 38T outer ring? I currently have a Race Face Atlas Crank which I want to keep...
    Yup, 38:16 works great. It's really close to running a 12/32 cassette with 22/32/42 rings. My 38t is a Black Spire. One site to check is http://www.speedgoat.com , they have lots of rings from several different companies.

    Monte

  3. #3
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    Quote Originally Posted by Monte
    Yup, 38:16 works great. It's really close to running a 12/32 cassette with 22/32/42 rings. My 38t is a Black Spire. One site to check is http://www.speedgoat.com , they have lots of rings from several different companies.

    Monte
    Thanks for your help, much appreciated
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  4. #4
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    If finding a 38t top ring is difficult you can get almost the same 38/16 ratio (2.38) with 42/18 (2.33) or 44/19 (2.32).

    Wombat

  5. #5
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    Yeah it is prooving difficult to find a 38T (I wonder why?) so thanks for the info.
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  6. #6
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    Rohloff Gearing

    Quote Originally Posted by Transition J
    Hi

    I am currently in the middle of purchasing a Rohloff Speedhub to fit to my Uzzi VPX (amongst others, as I'm hoping to be abel to chang eit form bike to bike), I am wondering how I'd go about making the gear spacing perfect.

    Currently I run a XTR 22/34T cassette and this gives the perfect spread of gears with my 36T/24T dual ring.

    I've been told to run a 38T chain ring and a 16T sprocket to get the right gearing, does this sound about right to you?

    Also do you know who makes a 38T outer ring? I currently have a Race Face Atlas Crank which I want to keep...

    I say run a 42t ring if you've got the 16t sprocket on the hub. I set up my Surly Instigator that way, and it corresponds almost perfectly to the 22-42/44x11-30/32 rigs I'd been running. Maybe just a hair wider at each end.

  7. #7
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    What would this work out to on a 29er with the 42t ring and 16t sprocket? I am running a 30/44 with an 11/34 rear cassette on my scalpel. This gearing works out nicely and I wouldn't mind keeping this or going a little wider at each end.

    Jeff

  8. #8
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    Reputation: Monte's Avatar
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    Quote Originally Posted by Jeff Spahn
    What would this work out to on a 29er with the 42t ring and 16t sprocket? I am running a 30/44 with an 11/34 rear cassette on my scalpel. This gearing works out nicely and I wouldn't mind keeping this or going a little wider at each end.

    Jeff
    42/16 is big gearing. 38/16 is closer to regular 26" gearing, not 42/16. On a 29er you'd need something smaller than 38/16 to be close. I think 17 is the biggest cog for a Speedhub, so the chainring needs to be smaller. I haven't done the math yet, but will at some point as I'm building a 29er soon.

    Monte

  9. #9
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    I managed to find an e13 G-Ring in 38T, is very light, the only trouble I'm having now is finding shorter bolts to fit it to the crank snuggly as the standard Race Face bolts are slightly too long...
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  10. #10
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    I got the numbers crunched, and this is what they say:
    If I understand you correctly, and you're running a 2x9, then I would recommend a 40x16 gearing on the Rohloff. That would yield a bottom gear of 20.23"(you're running 22.94" on the Scalpel), and a top gear of 106.36"(vs. 104" on the Scalpel). The gear inches were calculated WITH a 29" wheel.
    Some other options are as follows:
    38x16:B=19.22", T=101.04"
    39x16:B=19.72", T=103.70"
    40x16:B=20.23", T=106.36"(recommended)
    42x16:B=21.24", T=111.68"


    Quote Originally Posted by Monte
    42/16 is big gearing. 38/16 is closer to regular 26" gearing, not 42/16. On a 29er you'd need something smaller than 38/16 to be close. I think 17 is the biggest cog for a Speedhub, so the chainring needs to be smaller. I haven't done the math yet, but will at some point as I'm building a 29er soon.

    Monte

  11. #11
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    Quote Originally Posted by Transition J
    Hi

    I am currently in the middle of purchasing a Rohloff Speedhub to fit to my Uzzi VPX (amongst others, as I'm hoping to be abel to chang eit form bike to bike), I am wondering how I'd go about making the gear spacing perfect.

    Currently I run a XTR 22/34T cassette and this gives the perfect spread of gears with my 36T/24T dual ring.

    I've been told to run a 38T chain ring and a 16T sprocket to get the right gearing, does this sound about right to you?

    Also do you know who makes a 38T outer ring? I currently have a Race Face Atlas Crank which I want to keep...
    Here's what you'll need to match your (12)/34 cassette and 36/24 chainrings:
    chainring*wheel/cog=gear inches
    24*26/34=18.35 gear inches
    Rohloff cog=chainring*inner gear*wheel/gear inches
    RC=38*0.279*26/18.35=15

    38/15 will match your existing LOW GEAR. If you have been running a 2x9 setup you will have gained a bunch of top gears.

    Monte

  12. #12
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    Quote Originally Posted by Jeff Spahn
    What would this work out to on a 29er with the 42t ring and 16t sprocket? I am running a 30/44 with an 11/34 rear cassette on my scalpel. This gearing works out nicely and I wouldn't mind keeping this or going a little wider at each end.

    Jeff
    If I understand right, you have a 26" Scalpel and you want a 29er with the same gearing? If so:

    30/34*26=22.9 gear inches
    Cog=38*.279*29/22.9=13 (Rohloff does make a 13 tooth cog)
    Cog=42*.279*29/22.9=14 (they don't make a 14)
    Cog=44*.279*29/22.9=15.5 (they make a 15 and 16)

    The 42/16 would give you:
    chainring/cog*inner gear*wheel=gear inches
    42/16*0.279*29=21.2 (lower than what you have now)

    On the top end:
    44/11*26=104
    44/15*1.467*29=124.8 (even if you went a little lower bottom gear you are still way bigger on the top end. Probably too big.)

    Monte

  13. #13
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    Slightly OT, just a note on the 13T cog (based on Monte's last post)...

    The Rohloff 13T cog is unidirectional. Unlike the 15, 16 & 17T cogs which can be flipped (reversed) when worn to extract extra life from them, the 13T cog only threads on one way and therefore cannot be reversed.

    The 13T cog bumps out the Speedhub's chainline. The 15, 16 & 17T cogs all sit out at 54mm. The 13T cog extends it out another 3.5mm, to 57.5. This is done to clear the chain from the hub's shell (otherwise the chain would ride on the hub and not seat on the cog).

    In general, the smaller the cog, the faster it wears, reducing the life expectancy even more.

    Lastly, smaller cogs introduce greater inefficiencies to the drivetrain. I can't cite a source or a measurement, but I recall reading a Shimano tech claiming anytime you dip below a 15T cog, inefficiencies become "significant" on a non-derailleur drivetrain (implying derailleurs and some styles of tensioners introduce their own inefficiencies to a drivetrain).

    Just a little extra food for thought when picking out your ideal cog / chainring combo.
    speedub.nate
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  14. #14
    rohloff rich
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    Quote Originally Posted by Transition J
    I managed to find an e13 G-Ring in 38T, is very light, the only trouble I'm having now is finding shorter bolts to fit it to the crank snuggly as the standard Race Face bolts are slightly too long...
    Sheldon Browne's bike shop has the chainring bolts you need; they're made for track bikes. Just a note, though, you might want to think about having a bash ring to help keep the chain from derailling in which case you would use standard chainring bolts.

  15. #15
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    Standard chainring bolts can also easily be filed down.
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