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  1. #1
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    Rohloff ellip. chainring question

    Hello,

    I currently run a Rohloff Speedhub on my Ellsworth Id. I have the 17t cog/42t chainring set up. I'm going to buy a set of outboard bearing crank/BB. Rotor offers their Agilis crank with an elliptical chainring. They mentioned that the average teeth ran between 38 and 42.5 - average of 40t in general depending on where your pedal stroke was.

    Does running an elliptical ring with the Rohloff hub make sense? Will I run into the ratio issues - I know Rohloff recommends not dropping below a 2.4 ratio between front and rear cog/rings. If I go with the Rotor ring, will I need to adjust my current set up listed above?

    Also, is there a better cog/ring set up for the Speedhub for MTB/Xterra racing than my 17t/42t set up? I know there is some personal preference there.

    Thanks,

    Stephen

  2. #2
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    Look up Shimano biopace. I thought elliptical rings died decades ago.

  3. #3
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    A couple of current crank companies still included ellip.

    I'm not actually saying that I am excited about the elliptical rings - it is just that the Rotor company sells the ellip. rings with their cranks. The cranks can, of course, be used with round rings.

    Their argument makes some sense; however, I'm not the expert. My question may still be an interesting one in that an elliptical ring could violate Rohloff's ring/cog ratio depending on where a rider is in his pedal stroke, correct?


    Thanks,

    Stephen

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    Quote Originally Posted by swalters
    I'm not actually saying that I am excited about the elliptical rings - it is just that the Rotor company sells the ellip. rings with their cranks. The cranks can, of course, be used with round rings.

    Their argument makes some sense; however, I'm not the expert. My question may still be an interesting one in that an elliptical ring could violate Rohloff's ring/cog ratio depending on where a rider is in his pedal stroke, correct?


    Thanks,

    Stephen
    It could. Such a system would require a device (tensioner or derailleur) to take up and release slack in the chain as the elliptical ring rotates. If you've got a rohloff on a FS, you probably already run a tensioner and it's not a big deal. If your rohloff is on a HT, I'd imagine you could have a problem, especially if said frame is not set up with a derailleur hanger.

    For me, I think elliptical rings are ridiculous, and if some crank company was including them (forcing me to buy extra round rings if I wanted them), I would avoid the crankset no matter how good it's supposed to be.

  5. #5
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    A tensioner is not necessarily required for eliptical chainrings, because the average circumference remains approximately the same at any point in the rotation. For instance, with the ring described by the OP, there will always be approximately 20T engaging the chain, which equals 10 inches of chain. The small change in tension comes from the angle of the chain from the cog to the high point on the chainring, versus the low point on the ring. But in practice, this results in such a small difference in chain length that it doesn't need to be absorbed by a tensioner.

    As for the OP's question, it's not a problem: 38:17 is the ratio you'll need to calculate for, which is technically in violation of Rohloff's minimum 2.4:1 ratio. However, many of us dip below this ratio without problem. I wouldn't hesitate to run this.
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  6. #6
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    Quote Originally Posted by swalters
    Hello,

    Also, is there a better cog/ring set up for the Speedhub for MTB/Xterra racing than my 17t/42t set up? I know there is some personal preference there.

    Thanks,

    Stephen

    I like to run 36 tooth with a bash and 15 tooth sprocket on my mt. bike. It allows for much more clearance over rocks/roots/etc.

    Not sure on the ellipticals.

    Good luck!

  7. #7
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    I run a Rotor Q-Ring 36x16 with my Speedhub. FS with a Rohloff tensioner.

  8. #8
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    Ellip. Rings and chainline.

    Hello again,

    Thanks, Nate. So, do you actually ride ellip. rings? Do you think the tech. is good? It seems I see several companies moving back to having a version of ellip. rings - interesting concept.

    On another note, I have never paid attention to the 54 mm recommended chainline when using my Rohloff. I'm not even sure how chainline is adjusted - spacers etc.? Do most people simply buy their MTB crank of choice and make the adjustments?

    Thanks,

    Stephen

  9. #9
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    Nice - thnaks

    How do you like the Q-ring? Do you also ride the Rotor Agilis cranks? What do you think?

    What are the disadvanatge of my 17t/42t set up?

    SDW

  10. #10
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    Quote Originally Posted by swalters
    How do you like the Q-ring? Do you also ride the Rotor Agilis cranks? What do you think?

    What are the disadvanatge of my 17t/42t set up?

    SDW
    Are YOU, takin' to ME!?!

    I don't use their cranks, only the single Q-Ring. I use one on my SS and one on my Speedhub. Since I have been riding them that way for a long time, I can't answer your question. I suspect, taking them off would be the way for me to notice something faster, good or bad. My rings have held up well, but they are expensive, and I may not get them again.

    Disadvantanges? None I can think of unless you have to climb a lot of steep hills.

  11. #11
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    Quote Originally Posted by swalters
    Thanks, Nate. So, do you actually ride ellip. rings? Do you think the tech. is good? It seems I see several companies moving back to having a version of ellip. rings - interesting concept.
    I owned a bike that came with Bio-pace in '89. I didn't find them particularly offensive, and I rode that bike as much on pavement at high cadences as I did off road.

    Of the gobs of opinions of eliptical chainrings there is to read on the internet, one of the more convincing arguements has me believing that Bio-pace was perhaps flawed in its orientation, and that other elipticals can provide benefit under certain circumstances. But nothing has convinced me to switch away from round rings.
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  12. #12
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    So, Wish I Was Riding are you able to

    climb what anyone else does with the 36/16 set up? I may go ahead and give up my 42/17rig for your ring sizing. I've struggled lately on some steep stuff with the 42/17. Do you run the MTB ring version or a road Q ring?

    What cranks to do run?

    SDW

  13. #13
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    Quote Originally Posted by swalters
    climb what anyone else does with the 36/16 set up? I may go ahead and give up my 42/17rig for your ring sizing. I've struggled lately on some steep stuff with the 42/17. Do you run the MTB ring version or a road Q ring?

    What cranks to do run?

    SDW
    Yes, 36x16 is pretty comparable to a regular drivetrain. Works for me. I'm using a 5 bolt ring, with some cheap but effective Sugino cranks.

  14. #14
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    I can's seem to find a 36t mtb ring

    at the Rotor site - am I missing it?

    SDW

  15. #15
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    Quote Originally Posted by swalters
    at the Rotor site - am I missing it?

    SDW
    The 5 bolt ring is probably a road ring...

  16. #16
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    ... and if we just ... Pimpin!!!!!!!!!!!!!!!!!!

    Quote Originally Posted by Wish I Were Riding
    The 5 bolt ring is probably a road ring...
    I had the rotor crank setup cranks and rings for over 2 yrs loved them, there were on my spider 29er. I now have a Spec hard rock Ht adjustable chainstays perfect for my Rohloff speed hub. I will post pics soon just moved so thing are still everywhere the hub is the way togo, I havein't had a misshifts since I put mine on my bikes ubba baby.
    "It Is What It Is" Phil 4:13
    B-Ray Da Beast

  17. #17
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    Not everyone thinks they're ridiculous...

    http://www.bikeradar.com/news/articl...ro-ranks-17530

  18. #18
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    OK - so I've done soem additionl research and need some

    more advice.

    I was only looking at the Rotor Agilis cranks because they are the only 110 bcd MTB double I could find that would allow me to ride a 36t or 38t the Rotor Q Ellip. ring. All the other MTB Rotor Q-rings are 104 bcd and the only ring they have are 36 or 38t in the 104 bcd. I was trying to stick with the 36 or 38t because they seemed best for my Rholoff.

    On another board some sked why I didn't just go to a 34t, as Rotor does make a 34t 104 bcd, whihc would allow me to use any 104 crank (XTR ect.).

    So, my question is what would be the best 34t front and rear cog (15, 16, 17t - are there others for Rohloff) set up for the Rohloff. I don't mind violating the 2.4 ratio suggested by Rohloff. I have an old 15t in my garage the looks like it gets me close to the suggested ratio.

    Will I see any big difference with the 34t front ring over the 36 or 38? I did actually find a store, Superfily Cycles, that sells a 104 bcd 36 and 38t Rotor-Q ring, however, I think they are out of production - I may be able to get them in the future.

    Best,

    Stephen

  19. #19
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    Quote Originally Posted by swalters
    more advice.

    I did actually find a store, Superfily Cycles, that sells a 104 bcd 36 and 38t Rotor-Q ring, however, I think they are out of production - I may be able to get them in the future.

    Best,

    Stephen
    i found the 38t, but no 36t? i hope your right, and im missing something because its a 36t rotor ring in 104bcd that im after!

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