Recently I have sorted some old and recent made pinch rollers to came to the conclusion that no recent one in my possession surpasses in wow and flutter the original old Revox?s, although they look nicer!
Hey, that's exactly what I came up with a while back.
The original rollers on my Technics are tapered so the contact surface is only about 1/16th of an inch on either side of the tape width (that's just a guestimate, it could be smaller). I believe the difference in performance is due to the amount of tape stretch that the deformation of the roller surface causes as it pushes against the capstan. The wider (larger) contact patch of a new, more compliant or physically wider roller is in more intimate contact with the capstan surface around the tape or before and after the primary contact area. I believe that because the roller has a different diameter outside of the primary contact area, the capstan tries to rotate the roller surface at differing rates forcing the tape to either slip or stretch. Either way this causes speed irregularities which mimic the classic "stick/slip" of scrape flutter.
In a perfect world, a dual capstan/roller system might minimize this but in reality, it might be simply changing this from "stick/slip" to "slack/tight" which might also effect tension and tape/head contact too.
It seems that the amount of tape path friction could also have a part in this mechanism. The head profiles (contact area) and condition or any other guides seems to distribute the amount of tension at any given point differently and whether it's stick slip or slack, this tension determines
where in the tape path these irregularities in speed are compensated.
Of course all these things are probably secondary to things like capstan surface finish and tape surfaces but, for the most part those are things that are design considerations and not really in our control to change.
That doesn't stop me from making home spun theories like the one I just outlined.
BTW For those who don't know better, these and many things I post here are the results of way too much time on my hands and a miss spent youth!