So I have this circa 2007 Calfee frame that is supposed to be "Gates compatible" according to the shop we got it from. Apparently all that means it has the requisite spacing between the two bottom brackets because it seems with a normal install configuration there is not enough clearance between the rear ring and the chainstay. The cranks are centered (no shift to one side or the other) and this frame does not have the increased ring clearance on the newer Calfee frames (that looks like a big dent). I am using the new Shimano Ultegra Hollowtech II tandem triple cranks (FC-R601/FC-R603) with a standard 68mm BB.

One poor solution is to try adding a bunch of spacers to the spider. Not my first choice.

What I have done (and need to validate) is to flip the rings and bolts around so the ring flange w/bolt heads is on the inside of the crank spider and this works perfectly for the clearance issue. The Ultegra spider seems perfectly capable of handling a ring on either the inside or outside. As a bonus, there is no way the belt will ever rub the chainstay as some people have experienced. So the question here is if mounting the rings this way would cause any known problems?

The second question is about the belt and tracking. I believe we have the rings in perfect alignment as measured by equal offset from the bottom tube. I have not yet tightened the eccentric, but slipped the belt on with some slack remaining. With this loose mock-up, the belt simply slips off the side without any restraint. The question is, at what point does the belt teeth sink in past the lower of the ring edges so that it will stay in the tracks? Does full engagement only occur with the full tension applied?