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BBG -- Bottom Bracket Gears

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  • Larry
    Does anyone know if you can take a rear wheel IGH and use it at the bottom bracket location by holding the outside casing and rotating the shaft? What would
    Message 1 of 9 , Aug 15, 2011
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      Does anyone know if you can take a rear wheel IGH and use it at the bottom bracket location by holding the outside casing and rotating the shaft? What would happen with the gearing cable(s)?
    • Rich W
      Welcome to the group. On units with the shift cable attaching through the hub axle end you would tear up the shift cable. Even on other units the shifting
      Message 2 of 9 , Aug 15, 2011
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        Welcome to the group.

        On units with the shift cable attaching through the hub axle end you would tear up the shift cable. Even on other units the shifting cables are fixed rotationally in relation to the axle. It would take a total shifter redesign to get one that the cables remained fixed in relation to the hub shell.

        If the outer hub shell is bolted to the bottom bracket and the pedal crank arms are attached to the axle then where could you take the drive to the rear wheel from? I find it hard to picture an arrangement that would work. Such an arrangement would also give a very wide "Q factor".

        Another problem with your proposed arrangement is that I do not know of an IGH designed for rear wheel fitment that could likely stand up to the torque input it would receive with direct drive from the crank arms and pedals. There is a reason that Rohloff, Sram and NuVinci list minimum input ratios for their hubs.

        BB bicycle transmissions have been made all the way from 2 speed upto a recent German design prototype that is 18 speeds if memory serves. The German one was discussed here about 6 months ago as I recall. Projected price was well above that of a Rohloff IGH.

        Also a number of IGH units have been installed in bikes as intermediate transmissions fitted between the BB and rear wheel. This has been relatively common on some tricycle designs. The output sprocket to the rear axle is bolted to the IGH hub shell one way or another.

        Sorry to be a spoilsport but I do not see how to install a IGH designed for rear wheel installation in the BB position.

        Rich Wood


        --- In Geared_hub_bikes@yahoogroups.com, "Larry" <t.light@...> wrote:
        >
        > Does anyone know if you can take a rear wheel IGH and use it at the bottom bracket location by holding the outside casing and rotating the shaft? What would happen with the gearing cable(s)?
        >
      • jssr67
        ... You _can_ possibly do that, but it will give strange results, due to the freewheeling and/or coaster brake. These hubs are made for using a relative
        Message 3 of 9 , Aug 16, 2011
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          --- In Geared_hub_bikes@yahoogroups.com, "Larry" <t.light@...> wrote:
          >
          > Does anyone know if you can take a rear wheel IGH and use it at the bottom bracket location by holding the outside casing and rotating the shaft? What would happen with the gearing cable(s)?
          >


          --- In Geared_hub_bikes@yahoogroups.com, "Larry" <t.light@...> wrote:
          >
          > Does anyone know if you can take a rear wheel IGH and use it at the bottom bracket location by holding the outside casing and rotating the shaft? What would happen with the gearing cable(s)?
          >

          You _can_ possibly do that, but it will give strange results, due to the freewheeling and/or coaster brake. These hubs are made for using a relative movement between sprocket and axle to force-move the shell, they do not always adequately force-move the sprocket by a relative movement between axle and shell (gladly, otherwise the cranks on normal bikes would constantly turn).

          As an example, I show with a SRAM S7, with neutral gear at 4 of 7.

          Assuming you would keep the orientation of the hub, i.e. the chain sprocket to the right; also assuming you somehow manage to handle the problem that the shifter pin and sleeve could tend to drill a hole somewhere inside because they are not meant to rotate relative to the axis (but will relative to the pedal cranks).

          Your old "neutral gear 4" setting then will become another type of "neutral gear": no matter what you do, the chain will not move forward, and it will move backward independent of the cranks.

          In the other gears, moving the chain somehow will force-move the cranks more likely than moving the cranks will put force on the chain. In some gears, the cranks might move forwards, in others backwards.

          Not something that will drive you anywhere comfortably.
        • pj
          As mentioned, Shimano (three-speed) and Sturmey-Archer (three- and five-speed) both make IGH models that are designed for use as intermediate transmissions.
          Message 4 of 9 , Aug 16, 2011
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            As mentioned, Shimano (three-speed) and Sturmey-Archer (three- and five-speed) both make IGH models that are designed for use as intermediate transmissions. The market for these is three-wheeled cycles and pedal cars. Sturmey even makes hubs (gearboxes) like this that have an additional reverse gear.

            Example (this trike is flipped over, upside down in the photo):
            <http://www.flickr.com/photos/28120463@N07/4005465760/>
          • L Wittig
            Note that the intermediate position with a Rolloff hub is also used on the Flevobike GreenMachine recumbent shown at
            Message 5 of 9 , Aug 16, 2011
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              Note that the intermediate position with a Rolloff  hub is also used on the Flevobike GreenMachine recumbent shown at http://www.flevobike.nl/en/products/greenmachine
               
              This bike fits a lot of my desire to have a clean looking design (and low grease).  But my larger interest is putting the gearing in what seems to me to be the “right place” for all bikes, without extra chains and weight.  With the gears in the BB taking the wheels off to transport the bike or fix a flat would make the back wheel almost as easy as the front.  It seems to me that it would also simplify a folding bike.  Similar to the IF Mode bike but with multiple gears instead of being limited to 2-speeds with the Schlumpf High Speed Drive.
               
              -- Larry W.
               
              From: Rich W
              Sent: Tuesday, August 16, 2011 2:21 AM
              Subject: [Geared_hub_bikes] Re: BBG -- Bottom Bracket Gears
               
               

              Welcome to the group.

              On units with the shift cable attaching through the hub axle end you would tear up the shift cable. Even on other units the shifting cables are fixed rotationally in relation to the axle. It would take a total shifter redesign to get one that the cables remained fixed in relation to the hub shell.

              If the outer hub shell is bolted to the bottom bracket and the pedal crank arms are attached to the axle then where could you take the drive to the rear wheel from? I find it hard to picture an arrangement that would work. Such an arrangement would also give a very wide "Q factor".

              Another problem with your proposed arrangement is that I do not know of an IGH designed for rear wheel fitment that could likely stand up to the torque input it would receive with direct drive from the crank arms and pedals. There is a reason that Rohloff, Sram and NuVinci list minimum input ratios for their hubs.

              BB bicycle transmissions have been made all the way from 2 speed upto a recent German design prototype that is 18 speeds if memory serves. The German one was discussed here about 6 months ago as I recall. Projected price was well above that of a Rohloff IGH.

              Also a number of IGH units have been installed in bikes as intermediate transmissions fitted between the BB and rear wheel. This has been relatively common on some tricycle designs. The output sprocket to the rear axle is bolted to the IGH hub shell one way or another.

              Sorry to be a spoilsport but I do not see how to install a IGH designed for rear wheel installation in the BB position.

              Rich Wood

              --- In mailto:Geared_hub_bikes%40yahoogroups.com, "Larry" <t.light@...> wrote:

              >
              > Does anyone know if you can
              take a rear wheel IGH and use it at the bottom bracket location by holding the outside casing and rotating the shaft? What would happen with the gearing cable(s)?
              >

            • pj
              ... In cycling, what goes around comes around. (Owww! Bad pun.) In 1895, most bicycle multi-gear designs were mounted in the bottom bracket. By the start of
              Message 6 of 9 , Aug 16, 2011
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                > But my larger interest is putting the gearing in
                > what seems to me to be the “right place”
                > for all bikes, without extra chains and weight.
                > With the gears in the BB...

                In cycling, what goes around comes around. (Owww! Bad pun.)

                In 1895, most bicycle multi-gear designs were mounted in the bottom bracket. By the start of WWI twenty years later, gears-in-the-hub dominated the market and have ever since.

                Maybe something has changed to make this a better idea, or maybe there's something that the folks who have worked on this idea for the last 120 years have missed - but rest assured, it has been tried and hasn't found significant success.
              • Wesley Smith
                While the Schlumpf BB may not enjoy widespread success, it is a pretty effective setup. ... While the Schlumpf BB may not enjoy widespread success, it is a
                Message 7 of 9 , Aug 16, 2011
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                  While the Schlumpf BB may not enjoy widespread success, it is a pretty effective setup.



                  On Tue, Aug 16, 2011 at 7:35 PM, pj <prester_john_in_cathay@...> wrote:
                   

                  > But my larger interest is putting the gearing in
                  > what seems to me to be the “right placeâ€
                  > for all bikes, without extra chains and weight.
                  > With the gears in the BB...

                  In cycling, what goes around comes around. (Owww! Bad pun.)

                  In 1895, most bicycle multi-gear designs were mounted in the bottom bracket. By the start of WWI twenty years later, gears-in-the-hub dominated the market and have ever since.

                  Maybe something has changed to make this a better idea, or maybe there's something that the folks who have worked on this idea for the last 120 years have missed - but rest assured, it has been tried and hasn't found significant success.


                • pj
                  ... A great many bottom bracket gear designs have worked well over the last 120 years or so. Since the advent of effective gears-at-the-hub in the early
                  Message 8 of 9 , Aug 17, 2011
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                    > While the Schlumpf BB may not enjoy widespread success, it is a pretty
                    > effective setup.

                    A great many bottom bracket gear designs have worked well over the last 120 years or so. Since the advent of effective gears-at-the-hub in the early 1900s, bottom bracket gears have never been a major factor in cycling.
                  • Rich W
                    I would add that once you get over 2 or 3 gears in the bottom bracket it looks like weight becomes a major factor. Both SR Suntour and a German company
                    Message 9 of 9 , Aug 17, 2011
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                      I would add that once you get over 2 or 3 gears in the bottom bracket it looks like weight becomes a major factor. Both SR Suntour and a German company designed bottom bracket mounted transmissions for use in special downhill racing bicycle designs a few years ago. The transmissions weighed in the 10+ pound range. The SR Suntour version has a link posted to more information in the Links area.

                      The rear wheel mounted IGH allows a input ratio that reduces the torque that the unit needs to handle by 50% or greater typically. This allows a major reduction in transmision size and weight. Thus the recent, and seemingly ever revived, discussion on primary input ratios. Go too low and the transmisioon may go bang! Too high and you cannot get the low gear that you may want.

                      The modern multi speed (>2) BB gear designs have all required special frame designs which precluded any other transmission. For many people one attraction of the wheel mounted IGH is that it allows conversion of almost any frame to IGH operation.

                      Rich Wood

                      --- In Geared_hub_bikes@yahoogroups.com, "pj" <prester_john_in_cathay@...> wrote:
                      >
                      > > While the Schlumpf BB may not enjoy widespread success, it is a pretty
                      > > effective setup.
                      >
                      > A great many bottom bracket gear designs have worked well over the last 120 years or so. Since the advent of effective gears-at-the-hub in the early 1900s, bottom bracket gears have never been a major factor in cycling.
                      >
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