aka: Dr. Cannondale
Join Date: Jul 2009
Bikes: I'd rather not count how many, thank you
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If they are downtube shifters, those levers will work with any number of speeds on the rear wheel in friction mode- your easiest solution if the number of speeds and number of index clicks are not the same. Turn the D-ring on the right side shifter from SIS to Friction and you are done. If we are talking about a brake/shift lever combination (often called a brifter) then the number of indexed clicks and freewheel speeds need to match.
7 speeds will not give you any performance improvement, all things being equal. However, if your current freewheel is a corncob(like 12-18) and you need more range, then a 14-28 or 13-26 6 or 7 speed will work with those shifters and derailleur- again, if the number of index clicks are the same at both ends, in index mode, otherwise in friction mode. If the 8 speed RD is a 600 tricolor/640X series, then 28 is probably the largest rear cog that will wrap.
Stay away from 8 speed freewheels- they are notorious for bearing failure.
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