Originally Posted by
e_guevara
The OP has separate crank and rings - not a whole crankset. The problem is IF the crank is the "old" Red with the rings being "new" Red. If that is indeed the case, any advantage of better shifting that the "new" (Yaw version) chainrings can provide will be moot since the ramp and pin timings essential for good shifting is "offset".
Ah, I missed that OP had older crankarms. The article I linked do agrees that they wont work with new rings but for different reasons than tne one you site (they tested standard cranks but I would assume the argument also implies to compact, although maybe not the issue with small ring not fitting).
Swapping chainrings
The improvements in front shifting come from a combination of the new Yaw front derailleur and drastically improved chainrings, which have been made significantly stiffer and include improved ramp and pin timing. Why not, therefore, just put the new rings on an old crankset and save some cash?
Turns out that is not such a good idea. The new rings may still be five-arm with a 130BCD (bolt circle diameter), just like other standard road rings, but SRAM now uses a hidden bolt behind the crankarm rather than five independent spider arms. That means that the new Red rings have to be rotated 180% in order to mount up to a regular crankset. The pin that normally sits behind the crankarm to prevent chain jam sits either to the left or right of the crankarm, making it useless.
Further, the inner ring doesn’t fit on a regular crankset at all unless you’re willing to file it down a bit. The tab that is intended to sit behind the crankarm on the new Red crank is a bit too long to attach to a five-arm spider on a regular crankset. Running an old little ring seems to mess up the spacing sufficiently to negate the advantage brought by using the new big ring.
Whether the improvement in shift quality that comes from the new rings is worth the risk of jamming the chain in between the rings and crankarm, and spending time filing the little ring, is up to you.