I know this is an old thread but I bought a b66 for my new schwinn and it also has the seat post that is narrow at the top I flipped it upside down and it fits perfectly so you don't have to over tighten itI bought a B33, which is one of the biggest ones they have. I tried it on my Basman but couldn't get it to work right with the odd seat post on that bike so I didn't get much ride time on it. Here it is on the new frame but it's not rideable yet. The biggest problem with this seat is that if you're on the heavier side, you have to tighten the seat clamp to where you think it's going to break off and then tighten some more. Also look at the B190 although it doesn't fit some bikes because of the double-decker springs in back. You might also look for a Lepper Primus saddle. Hard to get in the states but a real comfy ride. A friend has one on his Ruff Tango.
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