Gear Combo Guru
Join Date: May 2007
Bikes: road, commuter/tourer, hardtail MTB, touring tandem, cargo, folder
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I had setup our CDC rings as a single-side drive, with the belt rings in the outer position of 5603 triple cranks, flipped so that the flat side was against the crank spider and the open side faced outwards. There wasn't QUITE enough space behind the right crankarms for the belt rings to fit without being slightly distorted (pushed towards the inside by the crank), so I filed off 1 or 2 mm from the ring behind the crank to get the clearance needed. The belt wasn't running on this section, so I hoped it would be OK. In the end, the belt did rub a little on the back of the crank arm, and you can see where it lightly polished it, but no worse than many people do with their heels on the outside of cranks. This was with the 71 tooth belt rings, since the 69 tooth rings have a smaller radius, the cranks would be even closer to the ring with that size, thereby marginally increasing the problem.
This was my main motivation for switching to the CDX belt and rings because that setup is slightly narrower, and it's also possible to control the lateral position of the belt-ring a little because the bolt holes are laterally in the center of the ring rather than on the edge. With this setup, we have no belt / crank interference issues. As I've mentioned in other threads, anyone wanting to do this themselves should try to get the 5603 105 cranks not the newer 5703 because the 5603 has slightly more room behind the crank.
I therefore have a set of 71 tooth rings and belt that have about 10,000 kms on them, aren't showing any signs of wear, but have had some minor filing done to the rings. The 71 tooth rings JUST allow installation on a stock Co-Motion Speedster, but the fit is very tight even with the eccentric in it's most rearward position. In fact, that was the second motivation to get the CDX rings, so that I could increase the captain's saddle setback by moving the eccentric BB forward instead of moving the seat closer to the stoker, and also get the saddle closer to the ground while maintaining the same pedal to crank distance.