Originally Posted by
twocicle
I"m still scratching my head over which pieces you are fitting, especially since the tandem crankset axle lengths are different than the regular double crankset axle lengths. Maybe when you get some time to lay it all out for me/us, I'd see the light
Sorry, I forgot to take a photo tonight. I will describe it in more detail.
The tandem fsa slk triple crankset is designed to allow for an adjustable chain line to allow 69 or 73mm bob shells and have some misalignment to facilitate 135 to 140mm iirc rear end spacing. There is a huge compromise for a 135/142thru rear spacing when you run the cranks centred with a triple chainring. Converting to a 39/53t double on that crankset only makes it worse.
Option with the triple setup is to run all of the spacers on the non drive side but that screws up the Q factor by a lot justified to one side. Not at all ideal.
In that, I want to make it ideal and run the shorter spindle double crankset with proper chain line and equal Q factor. That said I loose the ability to offset the crank for the timing chain but that's not critical and with the system I have already it will be straight anyways. (Non tandem double crankset run reverse for captain)
only problem beyond that is ensuring that with the more narrow Q factor when I'm fabricating the frame I need to keep chainring and crank arm clearances in mind to make sure it will work. Not a big deal in the whole scheme of the design.
Di2 shift range is going to be normal with this setup but if I ran the two outer rings of the triple crankset you would need to space the fd further from the frame and the set screw on the di2 derailleur might not contact th frame in that case.
Crank system will be as follows:
captain- reversed side standard double slk crank with single timing chainring (from 2015 build)
stoker- standard slk double crank with 39/53t chain rings drive side, tandem timing side arm with spider and timing chain. This is opti,used for the 135/142x12 spacing I am building for.
I needed the tandem arm for the timing chain or try one of the same side timing systems that potentially screws with chain line of the main drive system. I already had the slk tandem system so it was just the getting a proper double crankset to integrate the two.
Sorry if that's repeating myself but it took a bit of work to come to my direction and some investment in finding the right crank arms to be compatible.
M