Originally Posted by T-Mar
Depending on SunTour's safety factor, the version of derailleur and type of dropout you have, it may be possible to run a 28T. The bottom line is that you would have to try it, to be sure. If you post your derailleur version and dropout brand/model, hopefully someone on the forum will have tried your particular combination and can post a definitive answer.
T-Mar, as usual, a very informative reply, thanks!
The RD I have is marked "Suntour Superbe" on it's face, and "Maeda Industries, LTD. Japan XB" on the rear. Thre are no other markings. It does not look like a "Pro" version, and is not marked as one.
The dropouts are Campagnolo. When I got the bike (assembled & ridable) it was configured with this RD and 26T cog, and they were working fine together. As near as I and the shop can tell, this bike is circa 1974. But then again, the fellow that's doing the restoration is almost positive that the bike would have come originally with Campagnolo stuff, not Suntour. He's pretty confident that the RD and FD were added later, as an upgrade. FWIW, the BB, headset, and both hubs are Campagnolo.
I have a spare wheel that I can put the 28T freewheel on for experimentation purposes, so I guess I'll give it a try when the frame gets back from the painter. I was hoping to make the swap while I was waiting, but another week or two of waiting won't kill me......I think......
Regards,
John D.