bgnukem wrote:I guess you'd also need a bigger lockring to fit a 13T top sprocket, as opposed to the smaller lockrings for the 11T and 12T top sprockets.
normally there is a slight recess in the second smallest sprocket if the smallest is an 11T or 12T one. The smaller lockring normally just sits nicely in this recess. A larger diameter lockring may engage with the serrations which are present on some second smallest sprockets, but it will also engage with fewer threads in the freehub body.
Would it not be possible to use a 'normal' 13T sprocket with a standard 7- or 8-speed spacer behind, rather then requiring a dedicated top sprocket with integral spacer?
Usually not; the reason is that the splines do not extend to the very end of most 7s freehub bodies. However there are exceptions
1) a 7s body that is threaded externally for UG sprockets (NB if it is UG only
) a HG cassette won't fit the spline without modification.)
2) an original 7s HG freehub body.
In either of the above cases you might get away with it, but realistically the lengths have to match +/- ~0.5mm if you want the lockring to hold the sprockets without bottoming out, whilst a flat top sprocket is still engaged sufficiently with the splines on the freehub body. An integral spacer type sprocket is a much safer bet, even if you have a 'long-spline' freehub body.
Before 11T sprockets the splines went full length on HG freehub bodies. However the so-called HG-C body had shorter splines on the same length body, so that an 11T sprocket could be fitted. Subsequent shimano freehub bodies are based on the HG-C pattern, in ever increasing lengths, so none have full-length splines.
Obviously you lose the serrations intended to engage with the lockring, but not sure how much of an issue that is and could be Loctite-d as Brucey suggests....
it works just fine.
Recently bought some 13-28 7S cassettes from SJS so they are a good call. Will keep the the top sprockets and lockrings when they are worn out, for future cassettes!
FWIW there are small variations in exact lengths so it isn't a bad idea to have a 1mm spacer or two on hand just in case you need it.