Re: Inner ring mounting
On the 2013 Tetra, I was able to install the rear CDX ring on the inside of our Ultegra R603 timing side spider, leaving approx 2mm clearance from the belt to the chainstay.
The front Ultegra R601 spacing is a bit narrower than the rear (as verified by Q-factor diffs), I guess Shimano didn't think perfect timing ring alignment was needed - at least for typical chain setups. So, I mounted that CDX ring on the outside of the spider and then shifted the EBB by 2mm to the driveside. The timing ring alignment is still out by approx 1-1.5mm, but with the CDX setup this appears to be tollerable.
Besides the purported benefit of having the timing load moved as close to the centerline as possible, another more trivial benefit is that the crank magnet for the Garmin sensor now has plenty of clearance between it and the belt.
Here is a shot of the rear ring/belt clearance achieved:
* note the little piece of frame saver tape on the chainstay. It's there as a wear indicator just in case any rub occurs... like when riding in wet, mucky conditions when grime buildup can occur. I may remove this once we gain more confidence there will not be any rubs on the frame.