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  1. #1
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    chainrings- how small is too small?

    I have always had a 32-34t ring on my bike with 18-21t cogs. I could use a 64 BCD 26t ring with a 16t cog for the same effect. it seems like the main reason for 30t + rings is memetic inertia from when we used 3x cranksets and just used the middle ring position. why are singlespeeders afraid of using smaller rings?

    pro for smaller rings:
    more clearance from ground- never any reason to put your rings closer to trail features.
    lighter (meh)
    more frame clearance- frame designers could make frames with shorter chainstays and room for fat tires without resorting to drastic frame designs like elevated chainstays
    64 or 96 BCD and various direct-mount crankset designs could make replacing rings cheap and easy.

    cons for smaller rings
    drivetrains wear out faster with fewer teeth (maybe not a big deal if they can be replaced cheap and easy)

  2. #2
    Always in the wrong gear
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    I ran a 28x17 for a while, and saw no ill effects.
    There's some evidence of faster wear, but honestly with a steel front ring and a steel surly cog, both will probably live longer than you will. (half kidding)

    There's some math that shows small gears are more likely to throw a chain, due to frame flex, but I did not experience that.
    disclaimer: i only did it for a few hundred miles before moving to a standard 32xwhatever, mostly because I occasionally toss on a 11-42 10speed cassette and wanted to minimize the parts I was installing/swapping. 26x42 is IMO, unusable for anything, and 32x42 is a decent 'sit and spin' climbing gear. I tried 28 initially, because that's what my RF cinch crank came with.

    Also, there were no 26t or 28t oval rings available when I bought my current oval ring; only 30/32/34/36t. I bought a 'Neutrino Components' ring because they were the only ones to offer a blue anodized one, so I went with a 32. They now offer an oval 26 and 28.

    https://neutrinocomponents.com/index...gory&id_lang=1

    (edit: 26 and 28 are direct mount only. 64bcd smallest is 30t). Bummer. I'm super happy with my Neutrino oval and would 100% buy again.

    I will say this: I did not care for the aesthetics of 2 small rings. It just looked funny.
    Donít modify the trail to match your skills, modify your skills to match the trails.

  3. #3
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    FWIW, BMX bikes traditionally had a 43/16 gear forever, then 39/14, 36/13, 28/10, and went as low as 22/8. Last time I checked, they backed off at the tiniest gear and 25/9 is still very common. People got over the aesthetics quickly.

  4. #4
    Always in the wrong gear
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    aesthetics are personal preference. It was purely observational.
    It's probably more to do with the chain stays on my mtb being much longer than a BMX.

    I think trials bikes look 'odd', too.

    either way, I successfully had 'small gears' on my Jabberwocky and it worked without issue.
    Donít modify the trail to match your skills, modify your skills to match the trails.

  5. #5
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    Running bigger chainrings and cogs is more efficient and components last longer. If clearance isn't an issue there's no reason not to use them imo.
    I brake for stinkbugs

  6. #6
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    Like above said the larger rings save some power loss, i.e. ceramic speeds crazy oversized derailleur wheels...

    The lowest i go on a normal ss is 17 rear (on a flexy steel frame). I go lower on my coaster brake bike just to save some lag time getting the thing to engage.

  7. #7
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    When I first started single speeding I used to run 28x19 cause that's what I had to make the gear I wanted work. The first time I single speeded the AZT300 I did it with a 26x18 for the mental boost of an easier gear. It also worked just fine.

    I later ran 30x20 and 30x21 for a while. I've also done some dingling where the smaller ring was a 24x25T, paired with a 30x19 it worked fine as a dingle granny but I wouldn't go 24x as a dedicated SS gear. I now run 32x usually 22.

    To me the 32x has a perceivable 'smoother' feeling in the drivetrain compared to the 26x and 28x of similar gearing, not much difference but noticeable. My frame wouldn't fit a 34x oval so 32 is as far as I went.

    I personally wouldn't go smaller than 28x just on feels, 26x and below does feel slightly different. I don't think I'd go larger than 32x for trail riding for clearance issues. I'd go 34 or 36 for gravelly type stuff maybe, if my frame cleared it.
    My experience for what it's worth.
    @adamalphabet

  8. #8
    Downcountry AF
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    Bigger rings allow for more teeth to be engaged, lower friction (more efficient), and less chance of dropping a chain. And of course lower rate of wear.

    I run an oval 34:20 on my main SS, 32:21 on 29+.

    I'm not a big fan of the micro-drive setup for MTB applications. It's a harsh environment and my drivetrain takes a pounding and sees a lot of miles. I error on the side of durability and reliability. I've even gotten away from aluminum cogs lately as they show wear after half a season.
    Rigid SS 29er
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  9. #9
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    interesting points. sounds like we're better off keeping the 30-34t rings. I got thinking about this because I was impressed with the super-short chainstays (yeah, that's a fetish of mine, now get off my lawn) on the Salsa Woodsmoke and Stache, but I wish there was a way around the crazy elevated chainstays to get around the big tire and chainring clearance. looks like that yoke on the Specialized Fuse Comp 6 Fatty is a nice compromise.

    chainrings- how small is too small?-fuse-6-fatty.jpg

  10. #10
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    I imagine the chain slap on that Specialized is significant, but I guess people don't seem to notice it...

  11. #11
    psycho cyclo addict
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    I run 36's and 34's on single speeds. Never been much interest for me in short chain stays.

    With the trend toward lower bottom bracket heights on some frames, I can see where a smaller ring could be beneficial but I'd rather use bash ring and leave a "signature"
    【ツ】 eDub 【ツ】

  12. #12
    The perfessor
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    Now I read somewhere that running smaller chainrings / cogs created more stress issues and wear than using larger (makes sense if considering rotations per mile) but have used as low as a 26T chainring on my FSR and though it has worn slightly, it's been running well for 4 years now.......the biggest issue is how much power the ratio you're running demands...........
    Rigid 29er Ti SS
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  13. #13
    Ride Fast Take Chances :)
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    Quote Originally Posted by *OneSpeed* View Post
    Bigger rings allow for more teeth to be engaged, lower friction (more efficient), and less chance of dropping a chain. And of course lower rate of wear.
    Only the first couple engagement teeth on the ring actually transmit torque. It's virtually the same for all ring sizes. The lower wear rate comes from having more overall load surface with the same load on each piece.

    Where does the less chance of chain drop come in? I haven't found difference in rings from 30-34.
    Making shit harder than it needs to be isn't awesome, it's just...harder.

  14. #14
    Downcountry AF
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    Quote Originally Posted by alexbn921 View Post
    Only the first couple engagement teeth on the ring actually transmit torque. It's virtually the same for all ring sizes. The lower wear rate comes from having more overall load surface with the same load on each piece.

    Where does the less chance of chain drop come in? I haven't found difference in rings from 30-34.
    My fault, there was two thoughts mashed into one. The wear, engagement, and chance of dropping I was referring to the cog not the chainring. Though to some degree it applies to both I suppose.
    Rigid SS 29er
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    Fat Lefty
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    Full Sus 29er (Yuck)

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

  15. #15
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    I use 22T or 24T chain ring. I ride a mountain bike in the pinelands in New Jersey. Lots and lots of junk on the ground. Logs mostly. I ride fixed gear and sometimes a coaster brake, and the chain wears before any chain ring or cog. I assumed that is because the chain needs to work forward and backwards.

  16. #16
    Always in the wrong gear
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    Quote Originally Posted by J.B. Weld View Post
    Running bigger chainrings and cogs is more efficient...
    Quote Originally Posted by *OneSpeed* View Post
    .... lower friction (more efficient)....
    But how much efficiency difference are we really talking about here? I'd be genuinely interested in seeing the numbers on this. I'm not saying you're wrong, but I just can't see it being "enough to matter".


    A paper investigating efficiency of derailleurs vs Rolhoffs shows drivetrain drag as well into the upper 90's% with many factors influencing the system drag, including of the determinations of drag being chain angle- with the largest and smallest being the most 'draggy'. reasonably, the best, straightest chainline has very little drag, mostly the RD jockey wheels, and that still allows 97% efficiency.
    A single speed bike would ostensibly be above 98% as measured in the study due to no jockey wheels, but obviously not 100%. I'd be skeptical that the difference in drag between a two extremes of 26x16 (47.5 gear inches) and a 36x22 (47.8 gear inches) is more than a few tenths of a percent.

    I'm not advocating for one extreme or another. just 'discussing on a discussion forum'.
    Donít modify the trail to match your skills, modify your skills to match the trails.

  17. #17
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    Quote Originally Posted by ARandomBiker View Post
    But how much efficiency difference are we really talking about here?


    I don't know exactly how much but I do know it's something. Also it's a fact that parts will last longer. How much? Again, don't know but some for sure.


    I wasn't saying that it's a big deal one way or another, only that if chainring clearance isn't an issue why not go bigger?
    I brake for stinkbugs

  18. #18
    Always in the wrong gear
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    Quote Originally Posted by J.B. Weld View Post
    I wasn't saying that it's a big deal one way or another, only that if chainring clearance isn't an issue why not go bigger?
    I do not intend this to be argumentative, ultimately we both agree the differences are very small, I do agree 'wear rate' is a consideration. Some folks want a little more bling than a humble steel Surly cog, so it's a more important consideration.

    Regarding the other point you make:
    Frame clearance or ground clearance?

    I just measured the difference (using calipers) between the 28t and a 34t RaceFace direct mount rings hanging in my garage. it was just over 1/2 an inch radius difference. (0.5355 inches)

    I've left my mark on more than a few large rocks, and broken one chain, due to misjudging. I'd happily take 3/4-1" more clearance using a 22x13 vs 36x21 (approx 32x19) if it was all the same.

    All in good fun. not looking to start a war, I'm riding 32x20 (29+) right now and likely always will range from 32x... 18 to 21.
    Donít modify the trail to match your skills, modify your skills to match the trails.

  19. #19
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    Quote Originally Posted by ARandomBiker View Post

    Regarding the other point you make:
    Frame clearance or ground clearance?



    Both. Chainring clearance has never really been an issue for me so I'd always go with a bigger combo if possible. For those who do experience clearance issues I vote smaller.
    I brake for stinkbugs

  20. #20
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    I have been running a 26t AbsoluteBlack oval ring for quite a while now. I always run my gearing 2:1 plus 2 teeth on my rear cog and it's always close. I ran 32x18 for a long time, and this 26x15 feels pretty much the same (maybe a little lighter in the pedaling). I was warned by know-it-all friends that I would be eating through chains, pedaling wouldn't feel as efficient, etc. Honestly, I put a lot of miles in every year and I haven't noticed a damn bit of difference. I enjoy the extra clearance, which is why I initially chose a small drivetrain. I was on a frame with a low BB and needed any amount of clearance I could get for large step ups on my local trails.

    chainrings- how small is too small?-20181123_123157.jpg

  21. #21
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    Quote Originally Posted by SingleSpeedSteven View Post
    I ran 32x18 for a long time, and this 26x15 feels pretty much the same (maybe a little lighter in the pedaling). I was warned by know-it-all friends that I would be eating through chains, pedaling wouldn't feel as efficient, etc. Honestly, I put a lot of miles in every year and I haven't noticed a damn bit of difference.


    26/15 is a slightly smaller gear than 32/18. I've never noticed any efficiency differences between geared bikes and ss's either but it's there and many claim to feel it. Most people don't care about a few watts one way or another, sounds like you made the right call for your area.
    I brake for stinkbugs

  22. #22
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    Quote Originally Posted by J.B. Weld View Post
    26/15 is a slightly smaller gear than 32/18. I've never noticed any efficiency differences between geared bikes and ss's either but it's there and many claim to feel it. Most people don't care about a few watts one way or another, sounds like you made the right call for your area.
    Right. I guess my point was, that like most things if you're not a high level XC racer who gets on a trainer and uses fancy doo-dads to measure efficiency then it probably doesn't make a difference. Obviously if you can feel it and it bothers you, then don't run it... but like I said, I put a lot of miles on my SS and I haven't noticed a difference.

  23. #23
    Always in the wrong gear
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    That's a good lookin' bike ya got there, Steven.
    Donít modify the trail to match your skills, modify your skills to match the trails.

  24. #24
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    Quote Originally Posted by ARandomBiker View Post
    That's a good lookin' bike ya got there, Steven.
    Thank you sir... my savings account didn't appreciate it but it rides mighty nice.

  25. #25
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    Quote Originally Posted by SingleSpeedSteven View Post
    I have been running a 26t AbsoluteBlack oval ring for quite a while now. I always run my gearing 2:1 plus 2 teeth on my rear cog and it's always close. I ran 32x18 for a long time, and this 26x15 feels pretty much the same (maybe a little lighter in the pedaling). I was warned by know-it-all friends that I would be eating through chains, pedaling wouldn't feel as efficient, etc. Honestly, I put a lot of miles in every year and I haven't noticed a damn bit of difference. I enjoy the extra clearance, which is why I initially chose a small drivetrain. I was on a frame with a low BB and needed any amount of clearance I could get for large step ups on my local trails.

    Click image for larger version. 

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    Nice bike! I am currently building up that exact frame, even the same color. If you don't mind me asking, what stem length did you end up running?

  26. #26
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    Quote Originally Posted by BrianU View Post
    Nice bike! I am currently building up that exact frame, even the same color. If you don't mind me asking, what stem length did you end up running?
    I am running a 55mm. Rides perfect, I really like it.

  27. #27
    eri
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    You pick a ratio, then you pick your chainring size. Smaller the chainring the smaller the rear cog. Half the teeth in front you half the teeth in the back so nominally it yeilds half the wear life. In fact its worse than half because the friction also is higher.

    The chain tension increases as the chainring gets smaller. The chain tension is linear with (crank length / chainring radius).

    Assuming 200lb rider with 175mm crank just standing on a pedal (not reefing upwards and bouncing like on a singlespeed) the chain tension in newtons is:

    52t: 1480.198145
    42t: 1832.626275
    34t: 2263.832458
    32t: 2405.321986
    22t: 3498.650162

    I'm guessing that bouncing up a hill on ss could double that number. EU requires chains to hold 8000 newtons. When engineering you're supposed to keep tension below 1/6th of min breaking strength, otherwise chain life suffers.

    Other thing... chain friction on sprockets is linear with chain force, this friction loss is a small number but its there.

    Given none of those tensions are less than 8000/6 I think right approach is to use the largest ring you can that will clear your trails.

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