Old 02-25-17, 10:11 AM
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Double to single (!) with right sided drive and SRAM Eagle

I'm looking to put together another tandem, and I think the tech is there to do a 1x chainring build now with SRAM Eagle. Hear me out. I would love to have any thoughts from the experienced users here. This will be my third tandem build. Here is a comparison of the current 10 speed 11-36 cassette that I have now compared to a SRAM Eagle setup:

HTML5 Gear Calculator

They are functionally the same. Sure, there are smaller gaps if you are constantly switching between the front chainrings, but in practice we shift the RD for the vast majority of shifts, and if we are going to hit a climb that will require easier gears I shift the FD ahead of time so we have that additional range when we need it (to avoid shifting the FD in situations of high torque). So, all of my gear shifts are a 12-17% jump on the cassette of the 11-36, and they remain in that range on the SRAM Eagle. But, the Eagle cassette has a 500% range and my current setup is 445%, so if anything there is a gain from the change, and there is never a concern about when and how to shift the front derailleur.

Actually, if you exclude the last 2 bailout gears and the 10t "bombing down the hill" gear, the average jump between the major gears is 14.8% on the Eagle, and 13.7% on the 11-36. I'm not sure if the difference is big enough to be perceivable.

This also makes it very feasible to make a right sided drive, use "regular" cranks," lighten up and simplify the setup.

Then we get to chainline for the drivetrain and timing belt. Fortunately, SRAM has a really excellent specifications document with chainline and chainstay clearance info.


SRAM Eagle wants a chainline of about 49mm +/- 2. The rear dropouts are 135 OLD. So, for the rear crank (see page 33 of the above), the wide axle 2x crank seems to be perfect for clearing the chainstays with the crank and giving 42.5mm from BB center to inner aspect of the inner chainring and 50.5mm to the big ring (within spec for Eagle, but could use an offset narrow/wide chainring to get it just right). Then, a 1x crank in the front (see page 47) would give a 43.7mm from BB center to inner aspect of chainring. This would make it an inner ring right sided timing chain, which would keep it out of the way.

To make it shift, I plan to use the X-shifter wireless electronic shifter with the "road" shifters. I'm a backer on kickstarter. I think this is the only way to integrate Eagle with a road bar setup.


I haven't seen any example of this being done, so I wanted to outline the build and see if anyone has any thoughts.
willhs is offline