single speed gearing ratio- Mtbr.com
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  1. #1
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    single speed gearing ratio

    I'm sure that this has been a discussion topic before, but...
    Regarding chainring/cog size, 32/18 is roughly equivalent to 34/??
    I'm assuming that a 34/19 would be ever so slightly taller than 32/18...

    What is the mathematical equation for this?

    I ask because I've been running 32/19 and really want to go a bit taller but the manufacturer of my bike does not recommend putting an 18 on in conjunction with 32. The chain ring would likely rub the chainstay, no good on a carbon bike!

    Also, apparently I'm in the market for a really sexy chain ring. suggestions?

    Thanks!

  2. #2
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    Quote Originally Posted by CoyoteNW View Post
    I'm sure that this has been a discussion topic before, but...
    Regarding chainring/cog size, 32/18 is roughly equivalent to 34/??
    I'm assuming that a 34/19 would be ever so slightly taller than 32/18...

    What is the mathematical equation for this?

    I ask because I've been running 32/19 and really want to go a bit taller but the manufacturer of my bike does not recommend putting an 18 on in conjunction with 32. The chain ring would likely rub the chainstay, no good on a carbon bike!

    Also, apparently I'm in the market for a really sexy chain ring. suggestions?

    Thanks!
    Yep a 34:19 would be close to a 32:18.. just a little harder.. not much though. I use absolute black oval rings on all my bikes and love them

  3. #3
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    32/18 = 1.78

    34/19 = 1.79

    Can't imagine the difference would even be perceptible.
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  4. #4
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    As others have show. If all variables are remaining the same and you just want to compare ratios on the same bike then just use an equation of chainring/cog.

    As for chainring I'll second the AB oval. It's on all my bikes and I wouldn't use anything else.

  5. #5
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    2 in the front, 1 in the back.

    For every two you go up or down in the chainring, go up or down one in the cog for basically same ratio

  6. #6
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    AB & Garbaruk ovals used here.
    The Garbaruk has longer teeth, but the same ovality.

  7. #7
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    What you need is a Gear Inch Calculator.

    Sheldon Brown's Bicycle Gear Calculator

    there's also easy apps you can use on your phone to figure out your gear ratio's.
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    Stop asking how much it weighs and just go ride it.

  8. #8
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    Here's what I use, it will allow you to compare two set-ups:

    Bicycle Gear Calculator

    It shows a 1/10mph speed difference.

    NordieBoy, those are indeed some long teeth!
    By continuing to browse my posts, you agree to send me cookies.

  9. #9
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    Quote Originally Posted by chazpat View Post
    Here's what I use, it will allow you to compare two set-ups:
    Uh, not saying mine is better than yours, but mine is better than yours.

    single speed gearing ratio-screen-shot-2017-09-16-9.39.03-pm.png
    Rigid SS 29er
    SS 29+
    Fat Lefty
    SS cyclocross
    Full Sus 29er (Yuck)

    Stop asking how much it weighs and just go ride it.

  10. #10
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    Quote Originally Posted by *OneSpeed* View Post
    Uh, not saying mine is better than yours, but mine is better than yours.

    Click image for larger version. 

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    With all due respect to the late, great Sheldon Brown, his doesn't even have any chainrings and sprockets you can drag around.
    By continuing to browse my posts, you agree to send me cookies.

  11. #11
    Always in the wrong gear
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    Quote Originally Posted by CoyoteNW View Post
    I'm sure that this has been a discussion topic before, but...
    Regarding chainring/cog size, 32/18 is roughly equivalent to 34/??
    I'm assuming that a 34/19 would be ever so slightly taller than 32/18...

    What is the mathematical equation for this?

    I ask because I've been running 32/19 and really want to go a bit taller but the manufacturer of my bike does not recommend putting an 18 on in conjunction with 32. The chain ring would likely rub the chainstay, no good on a carbon bike!

    Also, apparently I'm in the market for a really sexy chain ring. suggestions?

    Thanks!
    I must be on the Struggle-bus today. Why does the manufacturer not recommend a 32x18 again?

    if a 32 is gonna hit the chain stay, a 34 is going to be worse. It's a bigger radius.

    cog size is (IME) totally irrelevant, if you can get a chain to touch any part of the frame while mounted there is simply not enough tension. A properly tensioned chain should deflect like 1/2".

    I'm not calling BS, or starting trouble, I'm legit trying to understand why 32x19 is A-OK, and 32x18 is verboten, while 34x19 is A-OK.

    I've run a bunch of combos between 28x16 and 34x22 and never found one that wouldn't work because of the issues you describe.
    Donít modify the trail to match your skills, modify your skills to match the trails.

  12. #12
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    I agree ^^^ ....


    makes no sense a 32x18 would not work. I happen to run a 34x19 myself, but I would have no issues with a 32x18 also.

    You may need new chain you can the diameters too much. All depends on how much adjustment you have left in your tension system.
    Joe
    '18 Specialized Epic 29", Vassago Verhauen SS 29", '13 Santa Cruz Solo 27.5", XC, AM, blah blah blah.. I just ride.

  13. #13
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    For math, here's what I use;

    CR
    ----- x Wheel dia.
    Cog

    So for me;

    30
    ---- x 29 = 43.5
    20

    That's my number with my AB 28/30 (yeah, I use the higher number )

    Also, you may be surprised by how small of a change in that number changes how you climb technical stuff. I am sure my strength has gone up since I started riding SS this year, but I definitely notice I can climb more tech on this current 43.5 than I could with a 44 ish gear inch. YMMV

  14. #14
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    Apparently we have a serious problem with math in the mountain bike world Nubster had it right and you don't need anything else - no gear inch calculators, no wheel size, nothing. Divide the chainring by the cog and compare. It's really that simple when you are changing gear ratios on your bike (not comparing two different bikes). Can you guys not perform simple division?

    As far as the sizes go, maybe you need a larger chainring/cog setup so that the chain clears the chain stay? Not the chainring since obviously a bigger chainring will come closer to the chain stay, but maybe the chain itself will somehow hit the chain stay.

  15. #15
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    Quote Originally Posted by ARandomBiker View Post
    I must be on the Struggle-bus today. Why does the manufacturer not recommend a 32x18 again?

    if a 32 is gonna hit the chain stay, a 34 is going to be worse. It's a bigger radius.

    cog size is (IME) totally irrelevant, if you can get a chain to touch any part of the frame while mounted there is simply not enough tension. A properly tensioned chain should deflect like 1/2".

    I'm not calling BS, or starting trouble, I'm legit trying to understand why 32x19 is A-OK, and 32x18 is verboten, while 34x19 is A-OK.

    I've run a bunch of combos between 28x16 and 34x22 and never found one that wouldn't work because of the issues you describe.
    So... It was a misunderstanding on my part:
    It wasn't an issue of chain ring rubbing the chain stay, it was that you will get chain slap on the chain stay with 32/18.

  16. #16
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    Quote Originally Posted by Thor29 View Post
    Apparently we have a serious problem with math in the mountain bike world Nubster had it right and you don't need anything else - no gear inch calculators, no wheel size, nothing. Divide the chainring by the cog and compare. It's really that simple when you are changing gear ratios on your bike (not comparing two different bikes). Can you guys not perform simple division?

    As far as the sizes go, maybe you need a larger chainring/cog setup so that the chain clears the chain stay? Not the chainring since obviously a bigger chainring will come closer to the chain stay, but maybe the chain itself will somehow hit the chain stay.
    You are correct that all that I was needing was the simple division of CR/Cog, and you are right about the issue: chain slap, not CR rub.

  17. #17
    Always in the wrong gear
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    Ahh. I think we all assumed this was a bike with sliders or an eccentric bottom bracket, not a 'magic ratio'.
    The puzzle makes more sense with that info.
    Donít modify the trail to match your skills, modify your skills to match the trails.

  18. #18
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    Quote Originally Posted by CoyoteNW View Post
    So... It was a misunderstanding on my part:
    It wasn't an issue of chain ring rubbing the chain stay, it was that you will get chain slap on the chain stay with 32/18.
    Huh? How loose are you running that chain? There should pretty much zero chain movement on a properly tensioned SS.
    Joe
    '18 Specialized Epic 29", Vassago Verhauen SS 29", '13 Santa Cruz Solo 27.5", XC, AM, blah blah blah.. I just ride.

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