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How Low Can You Go?

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  • gordonKoppang
    In answer to Tom s question about the importance of underdrive and overdrive ratios in gear hubs, I repeat the assertion that a hub will always tolerate being
    Message 1 of 14 , Jan 11, 2011
      In answer to Tom's question about the importance of underdrive and overdrive ratios in gear hubs, I repeat the assertion that a hub will always tolerate being geared up, but it may not always tolerate being geared down.

      To limit the amount of torque put through their hubs, manufacturers specify a minimum sprocket ratio. For the Alfine 11, Shimano specifies that your smallest front sprocket must be at least 1.9 times larger than the sprocket on the hub. For Rohloff, the smallest front sprocket must be at least 2.35 times larger than the sprocket on the hub.

      Taken together, the minimum sprocket ratio and the hub's lowest internal ratio determine just how low your lowest gear can be without voiding the warrantee.

      For the Rohloff Speedhub, the relevant numbers are:

      Sprocket Ratio (2.35) x lowest internal ratio (.279:1) = .655:1

      In the lowest allowable gear for the Rohloff, one rotation of the pedals results in a two-thirds (.655) rotation of the rear wheel. It is interesting to note that a mountain bike with 22-32-44 chainrings up front and an 11-32 cassette on the rear wheel has a bottom gear of 22/32 or .687:1

      For the Alfine 11, the relevant numbers are:

      Sprocket Ratio (1.9) x lowest internal ratio (.527:1) = 1.00:1

      In the lowest allowable gear for the Alfine 11, one rotation of the pedals results in one rotation of the rear wheel. That might be enough "bottom end" for the young and the strong, but its' not enough for me.

      I ride a tadpole trike with a 20-inch rear wheel. Because we don't have to balance, trike riders can gear our machines lower than bicycle riders can. With a single 38t sprocket on the crank and a 13t sprocket on my Rohloff hub, my lowest ratio is .815:1 (perfect for the hills around here!).

      Cheers,

      Gordon
    • scittbrw@yahoo.com
      Gordon -- would you that number for an Alfine 8-speed? Thanks for the explanation. I want to gear down my Alfine but don t want to stress it out. Florida Rider
      Message 2 of 14 , Jan 12, 2011
        Gordon -- would you that number for an Alfine 8-speed?

        Thanks for the explanation. I want to gear down my Alfine but don't want to stress it out.

        Florida Rider


        On Jan 12, 2011, at 12:17 AM, "gordonKoppang" <gordonkoppang@...> wrote:

         


        In answer to Tom's question about the importance of underdrive and overdrive ratios in gear hubs, I repeat the assertion that a hub will always tolerate being geared up, but it may not always tolerate being geared down.

        To limit the amount of torque put through their hubs, manufacturers specify a minimum sprocket ratio. For the Alfine 11, Shimano specifies that your smallest front sprocket must be at least 1.9 times larger than the sprocket on the hub. For Rohloff, the smallest front sprocket must be at least 2.35 times larger than the sprocket on the hub.

        Taken together, the minimum sprocket ratio and the hub's lowest internal ratio determine just how low your lowest gear can be without voiding the warrantee.

        For the Rohloff Speedhub, the relevant numbers are:

        Sprocket Ratio (2.35) x lowest internal ratio (.279:1) = .655:1

        In the lowest allowable gear for the Rohloff, one rotation of the pedals results in a two-thirds (.655) rotation of the rear wheel. It is interesting to note that a mountain bike with 22-32-44 chainrings up front and an 11-32 cassette on the rear wheel has a bottom gear of 22/32 or .687:1

        For the Alfine 11, the relevant numbers are:

        Sprocket Ratio (1.9) x lowest internal ratio (.527:1) = 1.00:1

        In the lowest allowable gear for the Alfine 11, one rotation of the pedals results in one rotation of the rear wheel. That might be enough "bottom end" for the young and the strong, but its' not enough for me.

        I ride a tadpole trike with a 20-inch rear wheel. Because we don't have to balance, trike riders can gear our machines lower than bicycle riders can. With a single 38t sprocket on the crank and a 13t sprocket on my Rohloff hub, my lowest ratio is .815:1 (perfect for the hills around here!).

        Cheers,

        Gordon

      • palatine_ej
        ... SRAM i-Motion 9 coaster brake version has an upper limit as well as a lower limit. Maximum primary gear for a coaster is always an issue, at some point
        Message 3 of 14 , Jan 12, 2011
          >I repeat the assertion that a hub will always tolerate being geared up, but it may not always tolerate being geared down.

          SRAM i-Motion 9 coaster brake version has an upper limit as well as a lower limit. Maximum primary gear for a coaster is always an issue, at some point the brake will fail.

          > For the Alfine 11, the relevant numbers are:
          >
          > Sprocket Ratio (1.9) x lowest internal ratio (.527:1) = 1.00:1

          As stated earlier, wait and see, the 1.9 isn't a hard limit but rather a recommendation. If time is limited, the Rolhoff is available today.
        • Rich W
          Gordon; The difference between Rohloff and the Shimano 11 speed Alfine is that the Rohloff manual says the minimum ratio is mandatory or the warranty is
          Message 4 of 14 , Jan 12, 2011
            Gordon;

            The difference between Rohloff and the Shimano 11 speed Alfine is that the Rohloff manual says the minimum ratio is mandatory or the warranty is voided. The Shimano Alfine document which lists the 1.9:1 input ratio says it is suggested or recommended. To me that would indicate that you can almost certainly go lower safely.

            Certainly lower ratios have been used on the Nexus8/Alfine hubs and the NuVinci CVT without incident. My NuVinci documentation lists 2:1 as the minimum input ratio.

            BTW does anyone have a link to any Nexus 8 or Alfine 8 speed literature which spells out a minimum reconmmended input ratio? I have seen the Alfine 11 document but in all of my downlosding I do not remember seeing anything documented for the 8 speed Shimano hubs.

            Rich Wood

            --- In Geared_hub_bikes@yahoogroups.com, "gordonKoppang" <gordonkoppang@...> wrote:
            >
            >
            > In answer to Tom's question about the importance of underdrive and overdrive ratios in gear hubs, I repeat the assertion that a hub will always tolerate being geared up, but it may not always tolerate being geared down.
            >
            > To limit the amount of torque put through their hubs, manufacturers specify a minimum sprocket ratio. For the Alfine 11, Shimano specifies that your smallest front sprocket must be at least 1.9 times larger than the sprocket on the hub. For Rohloff, the smallest front sprocket must be at least 2.35 times larger than the sprocket on the hub.
            >
            > Taken together, the minimum sprocket ratio and the hub's lowest internal ratio determine just how low your lowest gear can be without voiding the warrantee.
            >
            > For the Rohloff Speedhub, the relevant numbers are:
            >
            > Sprocket Ratio (2.35) x lowest internal ratio (.279:1) = .655:1
            >
            > In the lowest allowable gear for the Rohloff, one rotation of the pedals results in a two-thirds (.655) rotation of the rear wheel. It is interesting to note that a mountain bike with 22-32-44 chainrings up front and an 11-32 cassette on the rear wheel has a bottom gear of 22/32 or .687:1
            >
            > For the Alfine 11, the relevant numbers are:
            >
            > Sprocket Ratio (1.9) x lowest internal ratio (.527:1) = 1.00:1
            >
            > In the lowest allowable gear for the Alfine 11, one rotation of the pedals results in one rotation of the rear wheel. That might be enough "bottom end" for the young and the strong, but its' not enough for me.
            >
            > I ride a tadpole trike with a 20-inch rear wheel. Because we don't have to balance, trike riders can gear our machines lower than bicycle riders can. With a single 38t sprocket on the crank and a 13t sprocket on my Rohloff hub, my lowest ratio is .815:1 (perfect for the hills around here!).
            >
            > Cheers,
            >
            > Gordon
            >
          • Jim K
            ... Here s an answer posted out in cyberspace: http://forums.mtbr.com/showpost.php?p=6882863&postcount=11 I have not followed the literature reference to
            Message 5 of 14 , Jan 12, 2011
              --- In Geared_hub_bikes@yahoogroups.com, "Rich W" <astronut1001@...> wrote:
              >
              > BTW does anyone have a link to any Nexus 8 or Alfine 8 speed literature which spells out a minimum reconmmended input ratio? I have seen the Alfine 11 document but in all of my downlosding I do not remember seeing anything documented for the 8 speed Shimano hubs.
              >

              Here's an answer posted out in cyberspace:

              http://forums.mtbr.com/showpost.php?p=6882863&postcount=11

              I have not followed the literature reference to verify the quoted limit of 1:2.0.

              Jim
            • Jim K
              ... Here s the troubleshooting guide at shimano - the 2.0 limit comes up in a section on coaster brakes - not clear it applies more broadly than that.
              Message 6 of 14 , Jan 12, 2011
                --- In Geared_hub_bikes@yahoogroups.com, "Jim K" <jim.kukula@...> wrote:
                >
                > I have not followed the literature reference to verify the quoted limit of 1:2.0.


                Here's the troubleshooting guide at shimano - the 2.0 limit comes up in a section on coaster brakes - not clear it applies more broadly than that.

                http://bike.shimano.com/publish/content/global_cycle/en/us/index/tech_support/tech_tips.download.-Par50lparsys-0018-downloadFile.html/11)%208%20Speed%20Trouble%20Shooting%20Guide.pdf
              • Tom
                ... In fact investigating further out in cyberspace - like the whole thread that post was from -
                Message 7 of 14 , Jan 13, 2011
                  > Here's the troubleshooting guide at shimano - the
                  > 2.0 limit comes up in a section on coaster brakes -
                  > not clear it applies more broadly than that.

                  In fact investigating further out in cyberspace - like the whole thread that post was from -

                  <http://forums.mtbr.com/showthread.php?p=6882863#post6882863>

                  that answer was pretty much poo-poo'ed by other posters and available information the posters on that thread could find indicates there is no factory documented input ratio limit for Shimano 8s.
                • cerberus 900
                  IIRC Sheldon brown s last post to the RBT:
                  Message 8 of 14 , Jan 13, 2011
                    IIRC Sheldon brown's last post to the RBT:
                    http://groups.google.com/group/rec.bicycles.tech/browse_thread/thread/96e06f57abba9019/df9bf2bfe960f2fe?q=sheldons+last+post&lnk=ol&

                    --
                    --Cerb


                    On Thu, Jan 13, 2011 at 4:48 AM, Tom <prester_john_in_cathay@...> wrote:
                    >> Here's the troubleshooting guide at shimano - the
                    >> 2.0 limit comes up in a section on coaster brakes -
                    >> not clear it applies more broadly than that.
                    >
                    > In fact investigating further out in cyberspace - like the whole thread that post was from -
                    >
                    > <http://forums.mtbr.com/showthread.php?p=6882863#post6882863>
                    >
                    > that answer was pretty much poo-poo'ed by other posters and available information the posters on that thread could find indicates there is no factory documented input ratio limit for Shimano 8s.
                    >
                    >
                    >
                    >
                    >
                    >
                    > ------------------------------------
                    >
                    > Yahoo! Groups Links
                    >
                    >
                    >
                    >
                  • Simon Boddy
                    Hi Gordon et al, me again on this question of over-torquing hubs. I think we re too focussed on the manufacturer s specifications in this discussion. If we
                    Message 9 of 14 , Jan 14, 2011
                      Hi Gordon et al,

                      me again on this question of over-torquing hubs. I think we're too focussed on the manufacturer's specifications in this discussion. If we look at a hub as the meat in the sandwich, on top we have everything that produces torque on the input side : a strong rider, long cranks, big chain rings, small sprockets. On the bottom, we have everything that stops the hub from turning : the gradient, wheel size, weight of bike and rider. On the input side, by far the most variable factor is the rider, over which the manufacturer has no control ;-) A strong rider, jerking on the cranks while pulling up on the bars can exert a force several times his own weight on the pedal. But I contend this won't be a problem unless the matching conditions are present on the output side : a big wheel bike, in the easiest gear, on a steep grade with a heavy rider or load. Having no control over most of these factors, manufacturers have to set a limit of chainring to sprocket size they think will keep them out of trouble. As owners and users of the equipment, we can think about the whole situation.

                      Gordon on the input side you've said you're not a young fella, you just want to be able to wind up hills gently. On the output side you've got small wheels, which, all other things being equal, reduces the load on the hub proportionally (ie by 35%). I'd suggest you're out of the danger zone, you can put whatever gearing you like on the trike.

                      Regards Simon

                      On Fri, Jan 14, 2011 at 1:14 AM, cerberus 900 <cerberus900@...> wrote:
                       

                      IIRC Sheldon brown's last post to the RBT:
                      http://groups.google.com/group/rec.bicycles.tech/browse_thread/thread/96e06f57abba9019/df9bf2bfe960f2fe?q=sheldons+last+post&lnk=ol&

                      --
                      --Cerb



                      On Thu, Jan 13, 2011 at 4:48 AM, Tom <prester_john_in_cathay@...> wrote:
                      >> Here's the troubleshooting guide at shimano - the
                      >> 2.0 limit comes up in a section on coaster brakes -
                      >> not clear it applies more broadly than that.
                      >
                      > In fact investigating further out in cyberspace - like the whole thread that post was from -
                      >
                      > <http://forums.mtbr.com/showthread.php?p=6882863#post6882863>
                      >
                      > that answer was pretty much poo-poo'ed by other posters and available information the posters on that thread could find indicates there is no factory documented input ratio limit for Shimano 8s.
                      >
                      >
                      >
                      >
                      >
                      >
                      > ------------------------------------
                      >
                      > Yahoo! Groups Links
                      >
                      >
                      >
                      >

                    • Jim K
                      ... There s the question of what set-up has undue risk of failure. Then there is the question of violating warranty conditions. Seems like Rohloff has
                      Message 10 of 14 , Jan 14, 2011
                        --- In Geared_hub_bikes@yahoogroups.com, Simon Boddy <joe.ninety90@...> wrote:
                        > As owners and users of the equipment,
                        > we can think about the whole situation.

                        There's the question of what set-up has undue risk of failure. Then there is the question of violating warranty conditions. Seems like Rohloff has publicized a limit enough to be able to enforce a condition on the warranty coverage. I'm not sure what sort of warranty Shimano offers with their hubs anyway, but if nobody can find a clear statement of a limit on the chainring-sprocket ratio, it sure seems like they can't properly enforce any kind of condition like that.

                        I was studying the Koga gearing options:

                        http://www.koga-signature.com/en/page.aspx?id=3142366

                        I took out my Workcycles Transport bike, with its Nexus 8-speed hub. I measured the "meters of development" per crank cycle - it seems quite close to these Koga numbers. That's really too tall for me. I am in gear 1 all the time and never in 8. The bike has roller brakes which aren't very powerful, so even if I could pedal up a big hill I sure wouldn't want to come down very fast!

                        The drivetrain is all hidden behind a full chaincase, so I'm not sure what I have. But my plan is to figure out how to unlace that chaincase and then to see how small a chainring will fit my cranks.

                        Jim
                      • Rich W
                        The Rohloff limits are clearly stated in their 100+ page manual which ships with every hub. They state that with the factory recommended input ratios the hub
                        Message 11 of 14 , Jan 14, 2011
                          The Rohloff limits are clearly stated in their 100+ page manual which ships with every hub. They state that with the factory recommended input ratios the hub will be safe even from Olympic class athletes so their input specifications are very conservative for ordinary mortals!

                          At the same time one of their major retailers in GB, Thorn Cycles, has an article for download titled "Living with a Rohloff" which discusses going considerably lower than the Rohloff recommended gearing. A link to the article is in the Links area. It does state that such gearing is at the owners risk. Their designer is an adventure cyclist in places such as the Andes so wants very low gearing for some of the riding conditions he sees.

                          Even at recommended input ratios strong and/or heavy riders who were not spinners were known for breaking the occasional AW and lots of early Shimano IGH units per my reading. A hub designed for the average 120 pound Japanese rider did not like the 200+ pound American ones.

                          Rich Wood


                          --- In Geared_hub_bikes@yahoogroups.com, "Jim K" <jim.kukula@...> wrote:
                          >
                          >
                          > --- In Geared_hub_bikes@yahoogroups.com, Simon Boddy <joe.ninety90@> wrote:
                          > > As owners and users of the equipment,
                          > > we can think about the whole situation.
                          >
                          > There's the question of what set-up has undue risk of failure. Then there is the question of violating warranty conditions. Seems like Rohloff has publicized a limit enough to be able to enforce a condition on the warranty coverage. I'm not sure what sort of warranty Shimano offers with their hubs anyway, but if nobody can find a clear statement of a limit on the chainring-sprocket ratio, it sure seems like they can't properly enforce any kind of condition like that.
                          >
                          > I was studying the Koga gearing options:
                          >
                          > http://www.koga-signature.com/en/page.aspx?id=3142366
                          >
                          > I took out my Workcycles Transport bike, with its Nexus 8-speed hub. I measured the "meters of development" per crank cycle - it seems quite close to these Koga numbers. That's really too tall for me. I am in gear 1 all the time and never in 8. The bike has roller brakes which aren't very powerful, so even if I could pedal up a big hill I sure wouldn't want to come down very fast!
                          >
                          > The drivetrain is all hidden behind a full chaincase, so I'm not sure what I have. But my plan is to figure out how to unlace that chaincase and then to see how small a chainring will fit my cranks.
                          >
                          > Jim
                          >
                        • j_tdd
                          Rich, I just found Shimano s recommendation for ratio. It is (at least for a Nexus SG-8R31), in their technical document. It does mot explicitly warn against
                          Message 12 of 14 , Jan 31, 2014

                            Rich,

                            I just found Shimano's recommendation for ratio.  It is (at least for a Nexus SG-8R31), in their technical document.  It does mot explicitly warn against very low ratios, but do we assume that is what they mean?

                            http://www.shimano.com.au/media/techdocs/content/cycle/SI/Nexus/InternalHub/SG8R31_36/37J0A-001_SG-8R31_36-EN_v1_m56577569830638076.pdf


                            Long link, so just google "Shimano Nexus SG-8R31."    To quote Shimano:

                            "It is recommended that you set the chainrings so that the gear ratios are 

                            approximately 2.1. 

                            Example: F36T – R16T, F38T – R18T, F46T – R22T"

                          • Irvine Short
                            ... I bought a bunch of ex Rotalis touring bikes that they sold of as end of life here in Cape Town. 28 wheels, F32T - R22T It is a bit low for city use but
                            Message 13 of 14 , Feb 6, 2014
                              On Fri, Jan 31, 2014 at 9:19 PM, <j_tdd@...> wrote:

                              "It is recommended that you set the chainrings so that the gear ratios are 

                              approximately 2.1. 

                              Example: F36T – R16T, F38T – R18T, F46T – R22T"


                              I bought a bunch of ex Rotalis touring bikes that they sold of as end of life here in Cape Town.

                              28" wheels, F32T - R22T

                              It is a bit low for city use but offroad we sometimes go right down the bottom. Apart from the water damage which was fixable they are 100% OK. Rotalis must have hundreds of these bikes around the world.



                            • Colin Bryant
                              I ve always read recommend as a starting point, not a minimum or maximum.  I ve been using F30t/R18t, for about 24,000km (15,000mi), on my Alfine 11.   --
                              Message 14 of 14 , Feb 7, 2014
                                I've always read "recommend" as a starting point, not a minimum or maximum.  I've been using F30t/R18t, for about 24,000km (15,000mi), on my Alfine 11.
                                 
                                --

                                Colin

                                 


                                From: "j_tdd@..." <j_tdd@...>
                                To: Geared_hub_bikes@yahoogroups.com
                                Sent: Friday, January 31, 2014 11:19:52 AM
                                Subject: [Geared_hub_bikes] Re: How Low Can You Go?

                                 
                                Rich,
                                I just found Shimano's recommendation for ratio.  It is (at least for a Nexus SG-8R31), in their technical document.  It does mot explicitly warn against very low ratios, but do we assume that is what they mean?
                                http://www.shimano.com.au/media/techdocs/content/cycle/SI/Nexus/InternalHub/SG8R31_36/37J0A-001_SG-8R31_36-EN_v1_m56577569830638076.pdf

                                Long link, so just google "Shimano Nexus SG-8R31."    To quote Shimano:
                                "It is recommended that you set the chainrings so that the gear ratios are 
                                approximately 2.1. 
                                Example: F36T – R16T, F38T – R18T, F46T – R22T"


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