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Re: [rootsradicals] Re: Kickback chain interference revisited...

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  • Pete B
    Nate, It from the photo s it would appear you have quite a bit of chain clearance over the top of the front Horizontal Tube of the FreeRad but inadequate
    Message 1 of 23 , Feb 14 7:49 AM
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    Nate,

    It from the photo's it would appear you have quite a bit of chain clearance over the top of the front Horizontal Tube of the FreeRad but inadequate clearance underneath. 

    Also looking at the photo of the bike in mock-up http://www.booboodog.net/images/bikes/xtra/xtra-os-1.jpg it would appear that the front tongue of the FreeRad may be sitting a little too low (see the attached pic). Possibly due to the unique geometry of the donor frame.

    Taking a look at the dimensions Surly settled on for the BD  http://surlybikes.com/frames/big_dummy_frame/ they appear to have designed it to have the front dropouts, rear dropouts and (theoretical) FreeRad Mount points in a flat plane. Whereas it appears your's drop by around 1 inch where the FreeRad attaches to the donor frame dropouts.

    Also they spec their Bottom Bracket centre at 1.6 inches below the plane from front to rear dropouts. Your setup appears to be around 4 inches.
      
    You could try changing the geometry by raising the height of the Front attachment point of the FreeRad, You could do this by stacking washers between the tongue and the chainstay bridge plate or by sitting it on top of a FAP resting on top of the chainstays.

    Every bit you raise the front tongue will trade chain clearance above the bar for extra chain clearance under the Kickback stand.

    Just my 2 cents.

    Rgds
    Pete.B
     

    'Newspapers are unable, seemingly, to discriminate between a bicycle accident and the collapse of civilization' : George Bernard Shaw



    On 10 February 2010 09:06, speedub_nate <speedub.nate@...> wrote:
     

    --- In rootsradicals@yahoogroups.com, "Rich" <astronut1001@...> wrote:
    >
    > BTW with an eccentric bottom bracket is there any chance that the eccentric assembly can be rotated 180 degrees so that the chain run from the front chainring is moved enough to minimize or eliminate the interference with the Kickback?

     

    Yes, the EBB can hold the bottom bracket in either a "high" and a "low" position. Neither one offers the chain a straight shot in past the Kickback (basically, the "lowest" straight line the chain can run is limited by the forward bridge; the deployed Kickback impinges on this imaginary line.

    I'm going to take this to a local frame builder and ask if he can crimp the offending Kickback tube, then re-weld it to the plate that joins the two halves. I think that ought to do the trick.


  • speedub_nate
    ... sitting a little too low. Possibly due to the unique geometry of the donor frame. ... appear to have designed it to have the front dropouts, rear
    Message 2 of 23 , Feb 15 12:42 AM
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      --- In rootsradicals@yahoogroups.com, Pete B <nackterman@...> wrote:
      >
      > ...it would appear that the front tongue of the FreeRad may 
      > be sitting a little too low. Possibly due to the unique 
      > geometry of the donor frame.
      >
      > Taking a look at the dimensions Surly settled on for the BD 
      > they appear to have designed it to have the front dropouts, 
      > rear dropouts and (theoretical) FreeRad Mount points in a 
      > flat plane. Whereas it appears your's drop by around 1 inch 
      > where the FreeRad attaches to the donor frame dropouts.
      >
      > Also they spec their Bottom Bracket centre at 1.6 inches 
      > below the plane from front to rear dropouts. Your setup 
      > appears to be around 4 inches.
      >
      > You could try changing the geometry by raising the height of 
      > the Front attachment point of the FreeRad...

      Pete, good points, but I've got to give consideration to two things:

       - My head tube angle is right where I want it. Jacking the FR tongue higher would steepen this angle. This is something I can play with once I hit the road, but I'm smack in the 73.5°-74° range, and don't have more than .5° to 1° to play with. I estimate the head angle will steepen .5° for every 20mm I raise the FR tongue off the chainstay bridge, which isn't much, but it would take a lot of lift to get the chain to clear under the FR's front bridge.

       - The front wheel is 29"/700c, so compared to a 26" bike, the bottom bracket drop relative to the front axle is supposed to be lower (so as not to increase my center of gravity). The line you drew would be horizontal on a Big Dummy, but on this bike it slopes upward from the rear axle to the front axle. I realize the BB is slightly lower than ideal, but raising it would steepen the head tube angle.

      A 31T chainring arrived in Saturday's mail. I'll take some time Monday morning to get this thing on the road without the Kickback, and we'll see where that leads me. If it all works out OK, I'll plan a visit to my framebuilder to devise a way to crimp, grind and/or weld my way out of the kickstand/chain clearance problem.

      More to come...
    • speedub_nate
      ... I don t want to derail this topic, so I posted my first ride / first impressions and new photos on MTBR s cargo bike forum: http://bit.ly/cQbOh6
      Message 3 of 23 , Feb 18 3:14 AM
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        --- In rootsradicals@yahoogroups.com, "speedub_nate" <speedub.nate@...> wrote:

        > I'll take some time Monday
        > morning to get this thing on the road without the Kickback, and we'll
        > see where that leads me.
        >
        > More to come...

        I don't want to derail this topic, so I posted my first ride / first impressions and new photos on MTBR's cargo bike forum: http://bit.ly/cQbOh6

        I'll post back here when I make progress with the kickstand issue.

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