Why not more single pivot bikes with internally geared hubs?- Mtbr.com
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  1. #1
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    Why not more single pivot bikes with internally geared hubs?

    Hey everyone. I don't know too much on the engineering side of this, but it seems like one of the main reasons it's taken so long to come upon effective rear suspension designs that remain active when pedaling, and that don't act weird under braking, is the nature of most bicycle drivetrains- the angle then chain makes when you're in the 22-30 compared to the 42-11 is quite different, which in turn means that pedaling in each gear has a somewhat different effect on the suspension.
    But with an internally geared hub, the chain always works on the rear suspension in the same way when pedaling, so it seems like you could just make a single pivot bike with the pivot placement optimized around that one single gear. And front derailleur placement would no longer be an issue.
    I know that most of these problems have been more or less solved by now so it's a moot point, but I'm just looking back and wondering what you all think, and whether I am totally off base...
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  2. #2
    TNC
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    Mainly because the "gearbox" doesn't exist?...and I'm speculating much like you here. By "doesn't exist" I mean that there's no acceptable standard right now. Yeah, we have Rohloffs, but they're freakin' expensive and a little heavy...probably won't be an industry standard. I think the "derailleur-in-a-box" concept will hold the most promise, and I'm hoping SRAM will be the one to actually nail it down.

    There are some other issues that impact your idea here, but I think it's the acceptable gearbox that is the big hurdle.

  3. #3
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    Quote Originally Posted by uphiller
    Hey everyone. I don't know too much on the engineering side of this, but it seems like one of the main reasons it's taken so long to come upon effective rear suspension designs that remain active when pedaling, and that don't act weird under braking, is the nature of most bicycle drivetrains- the angle then chain makes when you're in the 22-30 compared to the 42-11 is quite different, which in turn means that pedaling in each gear has a somewhat different effect on the suspension.
    But with an internally geared hub, the chain always works on the rear suspension in the same way when pedaling, so it seems like you could just make a single pivot bike with the pivot placement optimized around that one single gear. And front derailleur placement would no longer be an issue.
    I know that most of these problems have been more or less solved by now so it's a moot point, but I'm just looking back and wondering what you all think, and whether I am totally off base...
    Yeah, I've thought the same thing. Having ridden high-forward pivot bikes for the last 5 years (superlight and heckler), I do find that certain gear combo's are more active than others. I think the problems at this point are in the excecution. First of all, the only good internally geared hub is still very expensive and fairly heavy. However, I have to think that if the demand were there, the price and the weight would both come down.

    Also, (this is my own speculation) in addition to the wieght of the hub, on a FS bike you have to deal with chain growth, so now you need a rear derailleur-like tensioner and/or some sort of chain guide in the front. Every time I consider loosing my front derailleur, I realize I will need some sort of guide in the front, and if that is the case I may as well just keep the derailleur. (except for the SS)

    I think right now these obsticals make it not worth the hassle to go with an internally geared single pivot, but that could change as technology progresses. However, there are other reasons that designers might want to with a linkags design in order to manipulate the axle path. That said, when/if internal hubs become the norm, the pedal feedback/bob issues with single pivots can be largely be eliminated.

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  4. #4
    "El Whatever"
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    Agreed with the others... there's the Rohloff, the G-boxx (Rohloff-in-a-can), the Honda gearbox, the Shimano-GT, the Petespeed now licensed by Hayes and some others that don't come to my mind now.

    There are options but none has stuck as for being much more complicated, heavier or simply much more expensive.

    We'll see more in the future but it's going to come slowly.

    Also... to many people still think that single pivots just suck and that changing the chain placement respective to the swingarm/final drive will not change much... especially braking wise. So, not much effort is being put there.
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  5. #5
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    pedal bob

    Quote Originally Posted by uphiller
    Hey everyone. I don't know too much on the engineering side of this, but it seems like one of the main reasons it's taken so long to come upon effective rear suspension designs that remain active when pedaling, and that don't act weird under braking, is the nature of most bicycle drivetrains- the angle then chain makes when you're in the 22-30 compared to the 42-11 is quite different, which in turn means that pedaling in each gear has a somewhat different effect on the suspension.
    But with an internally geared hub, the chain always works on the rear suspension in the same way when pedaling, so it seems like you could just make a single pivot bike with the pivot placement optimized around that one single gear. And front derailleur placement would no longer be an issue.
    I know that most of these problems have been more or less solved by now so it's a moot point, but I'm just looking back and wondering what you all think, and whether I am totally off base...
    The 3x8 or 3/9 ring/cog system is light, and relatively inexpensive, and addresses the need for the multiplied counter-squat requirement for lower gears when the acceleration pulse and vertical input into the pedals producing, more pedal bob, is much greater than higher gears. A much less lower gear reative optimized final drive with frame internal gearbox would have a smaller range of optimization. But platform shocks now aid the majority of designs currently that have somewhat similar suspension geometry limitations.

    There is a future for internal to frame gearboxes with one optimized drive line. Now that good climbing trail bike standards are up to 30 pounds or more with the advantages of travel over 6 inches or 4 inches with 29inch wheels, there is room for a couple more pounds of internal gearbox weight without any noticeable detriment in performance. A couple extra pounds is more noticeable with short travel and lighter bikes.

    It will take quite an investment for a very different frame configuration. And it would have very slow sales at first. The ring/cog set up has worked for trail biking for nearly 30 years. The long travel trail bike could facilitate the change, but probably only by custom builders at near a $10,000 price mark for a few decades.

    - ray
    Last edited by derby; 11-13-2005 at 10:33 AM.

  6. #6
    TNC
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    $10,000? Pfft! Chump change!

    Quote Originally Posted by derby
    The 3x8 or 3/9 ring/cog system is light, and relatively inexpensive, and addresses the need for the multiplied counter-squat requirement for lower gears when the acceleration pulse and vertical input into the pedals producing, more pedal bob, is much greater than higher gears. A much less lower gear reative optimized final drive with frame internal gearbox would have a smaller range of optimization. But platform shocks now aid the majority of designs currently that have somewhat similar suspension geometry limitations.

    There is a future for internal to frame gearboxes with one optimized drive line. Now that good climbing trail bike standards are up to 30 pounds or more with the advantages of travel over 6 inches or 4 inches with 29inch wheels, there is room for a couple more pounds of internal gearbox weight without any noticeable detriment in performance. A couple extra pounds is more noticeable with short travel and lighter bikes.

    It will take quite an investment for a very different frame configuration. And it would have very slow sales at first. The ring/cog set up has worked for trail biking for nearly 30 years. The long travel trail bike could facilitate the change, but probably only by custom builders at near a $10,000 price mark for a few decades.

    - ray
    Heck, order me a couple...LOL! Yeah, unfortunately for the internal gearbox, I think you're right. The problem of a standard, the problem of acceptance, and the problem of weight and money are big hurdles. One thing lately that seems to have boosted the potential life of the old derailleur/cog system is the emegence of more competition between the biggies Shimano and SRAM. I feel a lot better about the performance of my rear der and shifter combo with some of the latest stuff from SRAM. I have two bikes with top drawer Shimano and two with SRAM. I think there's a fairly noticeable performance increase with the SRAM. It has helped a lot with my problem of gearbox lust. I almost don't even think about it anymore.

  7. #7
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    Quote Originally Posted by TNC
    Mainly because the "gearbox" doesn't exist?...and I'm speculating much like you here. By "doesn't exist" I mean that there's no acceptable standard right now. Yeah, we have Rohloffs, but they're freakin' expensive and a little heavy...probably won't be an industry standard. I think the "derailleur-in-a-box" concept will hold the most promise, and I'm hoping SRAM will be the one to actually nail it down.

    There are some other issues that impact your idea here, but I think it's the acceptable gearbox that is the big hurdle.
    makes the Nucleon TFR (Rear travel 117 - 167 mm -- 4,5 to 6,5 inch), that costs and weights about the same of any high-end 6" travel enduro-free-ride machine
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    That Nicolai has four pivots, though, as far as I can tell.
    It just seemed to me that anyone could make a single pivot bike with an optimized chainline and then throw on a Rohloff speed hub. Chain growth issues could be solved by just using a single pulley rear tensioner attached to the derailleur hanger.
    No chain growth issues, no unnecessary pivots, no need for super-expensive platform valve shocks.
    I guess the real answer to my question is that the derailleur system, in spite of its flaws and the problems it creates for those trying to make suspension frames, has decades of refinement and financing behind it. That's not true to the same extent of internally-geared hubs. If the problems of the derailleur-equipped bike have already been solved, then there's no need to switch, I guess.
    But still- a single pivot bike with 4-bar performance would be just great.
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  9. #9
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    Its a Faux-Bar... in other words...a single pivot bike with a lot of extra pivots and links to actuate the shock off the main swingarm member the wheel happens to be attached to. The only suspension frame designs that adapt well NOW to internal geared rear hubs are the same ones that adapt to being setup singlespeed without a tensioner...URTs and Concentric-BB pivot Faux-Bars. Why? Effective chainstay length remains constant regardless of how much the suspension has compressed. Its this change in chainstay length that's prevented the majority of single-pivot bikes (and ones that behave as a single-pivot, even if they have weird linkages and such to vary the leverage ratio at different points of the suspension travel) from adopting a derailleur-less drivetrain setup.
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  10. #10
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    Quote Originally Posted by DeeEight
    Its a Faux-Bar... in other words...a single pivot bike with a lot of extra pivots and links to actuate the shock off the main swingarm member the wheel happens to be attached to. The only suspension frame designs that adapt well NOW to internal geared rear hubs are the same ones that adapt to being setup singlespeed without a tensioner...URTs and Concentric-BB pivot Faux-Bars. Why? Effective chainstay length remains constant regardless of how much the suspension has compressed. Its this change in chainstay length that's prevented the majority of single-pivot bikes (and ones that behave as a single-pivot, even if they have weird linkages and such to vary the leverage ratio at different points of the suspension travel) from adopting a derailleur-less drivetrain setup.
    Okay- changing chainstay length prohibits a singlespeed drivetrain. But couldn't you just as easily solve this problem by hanging a single pulley faux derailleur as a chain tensioner on the chainstay?
    Maybe one reason there are so few FS bikes which use a single optimized pivot and an internally geared rear hub, is that shock technology alone is not enough to get the ride kind of compression characteristics throughout the stroke, and additional pivot points are needed to get it just right.
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  11. #11
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    Quote Originally Posted by uphiller
    Okay- changing chainstay length prohibits a singlespeed drivetrain. But couldn't you just as easily solve this problem by hanging a single pulley faux derailleur as a chain tensioner on the chainstay?
    Maybe one reason there are so few FS bikes which use a single optimized pivot and an internally geared rear hub, is that shock technology alone is not enough to get the ride kind of compression characteristics throughout the stroke, and additional pivot points are needed to get it just right.
    That problem is solved in a better way on the GT bike... IMO, you want a bike like SpeedubNate's one... he has a Irohorse MKIII with a Rohloff and a chain tensioner. He swears by it.

    Apparently, Dave Weagle himself helped him to choose the chainrings/cogs for the bike. But don't quote me on that one.
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    Quote Originally Posted by uphiller
    That Nicolai has four pivots, though, as far as I can tell.
    It just seemed to me that anyone could make a single pivot bike with an optimized chainline and then throw on a Rohloff speed hub. Chain growth issues could be solved by just using a single pulley rear tensioner attached to the derailleur hanger.
    No chain growth issues, no unnecessary pivots, no need for super-expensive platform valve shocks.
    I guess the real answer to my question is that the derailleur system, in spite of its flaws and the problems it creates for those trying to make suspension frames, has decades of refinement and financing behind it. That's not true to the same extent of internally-geared hubs. If the problems of the derailleur-equipped bike have already been solved, then there's no need to switch, I guess.
    But still- a single pivot bike with 4-bar performance would be just great.
    The Nicolai is a single pivot. The other stuff you see is screws and links. The swingarm only pivots at one point.

  13. #13
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    gear box v hub

    from what I've seen and read about the gear box, you are limited to only 8-9 gears, which may be good for downhill but is never going to make it on a trailbike. The MBA review of the GT gear box didn't sound so promising, either. It was more like, "Sigh, let's wait another few years and see if they can get it right." And let's not forget the hoopla over Honda's bike. It took a corp of engineers to design the thing, and no one could see it for the longest time, but their fancy gear box didn't work so well and was swapped for one similar to GT's. But this seems really strange. How can Rohloff put all those gears in a hub, but no one can put as many in a gearbox? The only reason I would want a gear box over a hub is the weight distribution.

  14. #14
    "El Whatever"
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    Quote Originally Posted by Guyechka
    How can Rohloff put all those gears in a hub, but no one can put as many in a gearbox? The only reason I would want a gear box over a hub is the weight distribution.
    Nicolai's and all G-Boxx standard bikes have a Rohloff inside... the rest as someone said it's all screws and metal.

    Visit Nicolai and check out. There was some place where they showed the assy of a G-Boxx bike and how they put the thing in there.

    There are several reasons to have the gearbox in the middle of the frame. As you mentioned, weight distribution is a very important one but also braking behaviour, unsprung mass and such. This is why Honda rejected the gerabox but kept the design with the chain in the same place.
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