Originally Posted by
HillRider
Are you sure about the 13x25 having a loose 25T cog? I had a 13x25 9-speed Shimano cassette and believe the 21,23 and 25 cogs were on a single carrier.
The Shimano tech document for 6500 cassettes shows that the 13-25 and 13-23 cassettes both had single large cogs (25 or 23). I've assumed this was because they had no single 16 6500 cogs, the 16 is pinned together with the 17. The 19-21-23 or 18-19-21 cogs are mounted on common carriers. All of those sets were also used on other cassettes. It was probably more economical to use a single large cog on the 13-25 and 13-21. I have built a 13-25 using parts from a 12-25 and a single 16.
BTW the 14-25 is shown to have a single 23 and single 25.