Gearing Question

Discussion in 'Cycling Equipment' started by rplace13, Mar 23, 2010.

  1. rplace13

    rplace13 New Member

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    24 hours 46 views in the Single Speed section and nobody chimes in with some nuggets of info? Hard to believe there are bikers out there without opinions;) So trying here since it is somewhat equipment related.

    Here is a link to my original question but I'll try to shorten it up a bit
    http://www.cyclingforums.com/singlespeed/474455-gearing-question.html

    If you are trying to achieve a particular gearing does it matter how you arrive there? Is there any school of thought as to better/worse a big chain ring and big rear cog or a smaller chain ring and smaller cog or is a gear ratio simply a gear ratio? My gut tells me it does not matter...but curious if I have not thought it all the way through.

    Thanks!
     
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  2. genedan

    genedan New Member

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    One of my friends told me that there are differences in chain wear depending on what kind of gearing you use, for instance if you use something "weird" like 53/26 you can wear out your chain very quickly. But then again, that's for mutli-speed road biking and I don't know if it applies to single speeds.

    All of your gear choices in that other post seem "normal," so I guess you should just go with whatever feels comfortable. Anyways, using an atypical combination like big chainring, big sprocket, seems like a waste of metal to me since you probably achieve the same ratio with smaller gears.
     
  3. oldbobcat

    oldbobcat Well-Known Member

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    Small rear cogs (fewer than 14 teeth) wear significantly faster and put more friction into the drive because fewer teeth are engaged. Large front rings are heavier, less stiff, and require you to use a longer chain. My advice is to use a chainring that gives you the desired gear ratio with any rear cog in the 15-18t range.
     
  4. Akadat

    Akadat New Member

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    Going from thighbone length, through crank length, wheel diameter an tyre size to front an rear ratios, the final ratio is the answer except for what you find best for you.

    Bigger cogs front and rear will make the chain and gogs last longer and work better under the stress of ageing and wearin. The formula is highly variable.
     
  5. rplace13

    rplace13 New Member

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    Thanks all. The weight and wear-n-tear all make sense. Also all the variables makes it sound like it is very tough to nail down. I guess my ultimate question that I did not really articulate well enough is:

    Given the same end ratio is there any advantage/disadvantage to having more teeth up front? Weight and longevity aside. I'm wondering if starting from a dead stop, climbing or using my legs to slow the bike down is helped/hurt with the same ratios arrived at with different chain wheels/cogs? I don't think it would matter but not being a mechanical engineer or physicist I did not know for sure.
     
  6. alfeng

    alfeng Well-Known Member

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    If you have a larger chainring & rear cog for approximately the same ratio as a smaller combination then you will have more CHAIN WRAP with the larger chainring/cog combination ...

    Having more chain wrap is probably more meaningful if your chainline isn't close-to-perfect and/or if your chain is slightly slack (i.e., inadequate tension) because (if the latter occurs) the chain could theoretically crawl off of EITHER the rear cog OR the chainring more easily when there is less chain wrap than on a combination than when more teeth are engaged.

    Presuming a close-to-perfect chainline, your only concern would be between ROAD chainring/cog/chain vs. TRACK chainring/cog/chain -- you've sort-of indicated that you just want to use your existing ROAD components (i.e., chainrings) ...

    Since I'm not man-enough to ride Fixed, I set up my Single Speeds using ROAD gauge components.
     
  7. Tnark

    Tnark New Member

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    I read recently of an old study that found that using larger cogs results in a slightly more efficient drivetrain due to less friction, mainly due to the lower amount of chain wrap/bending over the rear cogs compared with a smaller rear cog, in which case the chain must bend and straightem more per link - makes good sense..


    Also if you are riding fixed, don't go for a ratio that gives you an exact number with the front to rear ratio eg 48/16 which is exactly 3.00 to 1, or to a ratio that is easily divisible into 1, eg 3.5, 3.25 etc. . You will end up with regular spaced flat spots on your rear tyre due to the regularly spaced application of maximum leg force during the crank cycle.
     
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