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An appeal to the brain trust

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  • gordonKoppang
    The Sinner Comfort trike can be fitted with a SRAM Dual Drive as a mid-drive. One chain goes form the crank to the DD cassette/ hub and another chain runs
    Message 1 of 3 , Apr 18, 2011
      The Sinner Comfort trike can be fitted with a SRAM Dual Drive as a mid-drive. One chain goes form the crank to the DD cassette/ hub and another chain runs form an output sprocket on the hub to a sprocket on the rear axle.

      Here's a picture: http://www.sinnerligfietsen.nl/mod66.html


      Running a 52/42/30 triple gives a hellish great range, but over-torques the hub (SRAM specifies a minimum sprocket size of 33t). Running a 20t output sprocket from the hub to a 23t sprocket on the axle would gear everything down by 15%.

      My question to the brain trust is this: Will a reduction on the output side counteract the over-torque on the input side (and give the hub internals a long life)?

      With thanks,

      Gordon Koppang
    • Rich W
      Gordon; In a mid drive application changing the output ratio has no effect on input torque per Rohloff documentation which covers that use. If a 10% torque
      Message 2 of 3 , Apr 19, 2011
        Gordon;

        In a mid drive application changing the output ratio has no effect on input torque per Rohloff documentation which covers that use.

        If a 10% torque overdrive worries you then go to a different cassette installed on the Dual Drive. Per my understanding any hyperdrive or SRAM 8 or 9 speed cassette will fit and be compatible with the shifters depending on whether you have a 24 or 27 speed DD shifter drivetrain. IIRC the 33 tooth front is shown coupled to a SRAM 11/34 cassette without exceeding factory listed drivetrain recommendations on the 27 speed version. Install a cassette with a 30 tooth or smaller largest sprocket and the 30 tooth smallest chainring should be fine as the factory ratio listed is a 33 tooth front ring and a 34 tooth max rear cassette sprocket.

        You could also just avoid using the small front ring and largest DD input sprocket combination and stay within listed limits. Remember too that real world the input ratio for a IGH is also dependent on rider weight and strength, things that manufacturers cannot factor into their recommendations.

        Rich Wood

        --- In Geared_hub_bikes@yahoogroups.com, "gordonKoppang" <gordonkoppang@...> wrote:
        >
        >
        > The Sinner Comfort trike can be fitted with a SRAM Dual Drive as a mid-drive. One chain goes form the crank to the DD cassette/ hub and another chain runs form an output sprocket on the hub to a sprocket on the rear axle.
        >
        > Here's a picture: http://www.sinnerligfietsen.nl/mod66.html
        >
        >
        > Running a 52/42/30 triple gives a hellish great range, but over-torques the hub (SRAM specifies a minimum sprocket size of 33t). Running a 20t output sprocket from the hub to a 23t sprocket on the axle would gear everything down by 15%.
        >
        > My question to the brain trust is this: Will a reduction on the output side counteract the over-torque on the input side (and give the hub internals a long life)?
        >
        > With thanks,
        >
        > Gordon Koppang
        >
      • Mike Wilson
        torque is torque. I believe peak tourque is higher on an upright than on a recumbent because you can stand on an upright - but I could be wrong and would like
        Message 3 of 3 , Apr 19, 2011
          torque is torque.

          I believe peak tourque is higher on an upright than on a recumbent because you can stand on an upright - but I could be wrong and would like to see data.

          10 percent may not be a big deal.

          The issue should be the gear ratio, not the one sprocket size.

          Torque also depends on the rider, something the minimum gear ratio specs don't mention. Gibby Hatton (or whoever the modern sprint champions are) driving a minimum-permissible-gear bike would probably break a lot of stuff.

          Can you change the ratio between the intermediate and the final such that the intermediate spins faster thus with lower torque?

          Michael Wilson
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