the 4 tooth rule and dingle (double) speed- Mtbr.com
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  1. #1
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    the 4 tooth rule and dingle (double) speed

    Hi again guys. I was reading about the "4 tooth rule" in the singlespeed FAQ's, where a 4 tooth difference b/w gears will result in (hopefully) the same chainlength. I've asked about about it here:
    http://forums.mtbr.com/singlespeed/w...es-752991.html
    But thought I'd start a new post. My question is:

    - would a "6 tooth rule" apply by the same reasoning (where, provided number of teeth for each gear ratio is the same, then the chain length remains the same)?
    - I ask this as I would use a White Industries DOS Eno freewheel, and I notice they do a 16/19 (I was originally looking at 17/19). Given the 16/19 has a wider spread (and I'm after a "flat/undulating" gear for singletrack, and a "***** of a sustained climb" gear), then could I do something like:

    - 16/35 & 19/32

    This still adds up to 51 teeth for each ratio (16+35=51, 19+32=51). Does tooth count translate directly to chainlength, provided no changes are made to positioning of EBB or rear axle position?

    I'd imagine this would be a pretty useful pair of gears on my 26".

    Would it mean that I'd just need to keep a 3 tooth difference between the front chainrings to keep the chain length the same (eg. 35/32, 36/33, 37/34, etc...)?

    I just wanna get my head around this before orderng odd-size chairings and a $100 freewheel!

    Thanks gang,
    Mat

  2. #2
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    It'll be very similar in length, but not exactly the same. You may have luck in getting it to work with slidding dropouts or an ebb, maybe one of your ratios will be tight and the other a bit loose, but still functionally fine, but you you may not. I've run two dinglespeed set-ups, both on horizontal type (read track end) drop outs. One was usually a 32/18 or 19 and 34/16 (the one tooth difference just meant it was slightly closer to the seat tube in the dropouts, no problem for track ends with disc brakes. At one point I also got away with running a 32/20 and 34/16, but the dropouts on my azonic were long and I added one slight spacer on my brake to get it a bit higher so it didn't rub (this was preemptive, don't know if it was really necessary). So, in theory, depending on your dropouts, you should be fine.

    PS: Dinglespeeds are much easier and cheaper to set up with a splined cassette style hub.

  3. #3
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    Thanks for the reply. I should elaborate. I have a Phil rear hub that runs freewheels only, and vertical dropouts, with tension managed by a Phil Eccentric BB. I am only wanting to set up 2 gears that I can change between without altering anything else. I need to be able to race with this setup. As an example, I am soon to do an event with a few killer climbs. The plan would be to run a "flatland" gear as long as possible, then quickly release rear QR, flick to the "climbing" gear when the going gets tough. Once the climb is conquered, it'd be back to the "flatland" gear, and so on. I am happy with the time penalty in this sense, but not willing to muck about with chain tension issues. So the aim is to have 2 gears with identical chainlengths. White Industries sells a rear Dos Eno as 16/19, 17/19 or 16/18. I reckon the 16/19 would be best for this purpose, as it has a bigger spread. BUT - can I put two chainrings (somewhere around 32-35) on the front and pull it off? Hmmmm...It'd be great to have some concrete assurance before spending around $150+ on the bits!
    Keep the ideas coming.

  4. #4
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    Hey, I think you might be out of luck really. Sorry to say. I actually run a forward eccentric BB on my nice single speed bike (a 2008 26" wheeled Kona Kula with non-moving vertical dropouts). I tried to run a dinglespeed, but could never get it where the chain wasn't either too tight, or too loose. You might have better luck though, but you're going to just have to try it out. Calculate your chainlength here : http://eehouse.org/fixin/fixmeup.php

  5. #5
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    Thanks mate. I had a bit of a look at that, but need to revisit it. What if I went with a "safer" 32/17, 34/19? It'd be great if anyone out there has run this setup! Feedback?

  6. #6
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    I hate to tell you this, but this set up is not any less likely to work. Although the numbers place it in a similar chain length, it'll almost never be EXACTLY the same. That link I sent you has chain length numbers with ratios. If you can get numbers to match up, then do it. But until then, I really wouldn't waste your money on a WI dingle freewheel. If you want to do this, you're going to have to invest in a frame with horizontal drop outs.

  7. #7
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    Cheers. I had a look at the chainlength part of the calculator. There's a few gears that may work. I dick around with it a bit more and see what comes together....

  8. #8
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    back brake?

    not "exactly", but it should be very close. i do a an eight tooth difference on a couple of bikes with a cassette hub, cogs, and spacers. works fine, but note that i use V brakes on the back, so i'm uncertain about tolerances and disc brakes.

    it would be interesting to hear more about the geometry/mathematics on this.

  9. #9
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    Quote Originally Posted by Cygnus View Post
    not "exactly", but it should be very close. i do a an eight tooth difference on a couple of bikes with a cassette hub, cogs, and spacers. works fine, but note that i use V brakes on the back, so i'm uncertain about tolerances and disc brakes.

    it would be interesting to hear more about the geometry/mathematics on this.
    I'll let you know what transpires. My bike has vertical drops and tension is via EBB, so brakes at the rear not an issue (the wheel can't move!).

  10. #10
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    Quote Originally Posted by mat-with-one-t View Post
    I'll let you know what transpires. My bike has vertical drops and tension is via EBB, so brakes at the rear not an issue (the wheel can't move!).
    Track ends and V-brakes might be an advantage when using a dingle, the track end allow for tiny differences in axle position to compensate for the slight differences in chain length.
    Ride more!

  11. #11
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    Quote Originally Posted by asphaltdude View Post
    Track ends and V-brakes might be an advantage when using a dingle, the track end allow for tiny differences in axle position to compensate for the slight differences in chain length.
    maybe, but the difference is still really small, even with an 8 tooth difference.

    i have horizontal dropouts, v brakes in the back, but also a surly chain tug to keep the wheel snug. when switching from a cruising gear to a climbing gear, or vice versa, there is no detectable difference in the wheel position, or the way the chain tug fits (without adjusting it).

  12. #12
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    I've done 4t apart (38/34x16/20) with mild success, and it looks like everyone is giving you good directions, so you're just gonna have to take the plunge.

    One thing that will help this succeed is having two quality chainrings to go with your freewheel. Then make sure everything is as centered as possible. Sheldon Brown with the hook up. Scroll down the "centering chainwheels" bit. I use my big crescent wrench.

  13. #13
    one chain loop
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    i scrolled down and saw a chopped fingertip, gross.
    everything sucks but my vacuum cleaner.

  14. #14
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    I've been running dinglespeed set ups on different bikes for years. I would recommend you start with a cassette hub rear wheel with cogs and spacers to figure out what ratios will work for you. That set up is cheap and lasts forever. You also have a choice of infinite combinations! You might find that you don't need to throw down all that cash for the DOS, especially if you find that the ratios they offer don't work for you.

  15. #15
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    Yeah I follow your reasoning. Thing is, I have the world's nicest rear, and I hope to keep it!!


  16. #16
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    That's a nice set up!
    If you want to experiment with a dinglespeed set up, without messing up your main ride, try using an old '80s-'90s MTB with horizontal dropouts. Then you can find out if changing ratios on the trail is practical or not. It might be practical on a long course, but not on a short course. Flipping the bike over ten - twenty times to change gears, eats up a lot of time!

  17. #17
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    Quote Originally Posted by fishcreek View Post
    i scrolled down and saw a chopped fingertip, gross.
    I'm surprised. I figured everyone on this forum was into amputee porn. Whatever.

  18. #18
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    Quote Originally Posted by umarth View Post
    I'm surprised. I figured everyone on this forum was into amputee porn. Whatever.
    I was always assured it was armless....

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