Originally Posted by
Steve B.
If you’ve invested in housing cutters as well as shifter cable cutters, it’s always cheaper to just buy bulk lengths of housing and individual cables. If the OP has those tools, then have at it. The advantage to the pre-cut kits is they are ready to go, no cutting tools needed, usually. KCT’ post shows an example where the kit lengths are not going to work, but I can say after 36 years and 20 some odd bikes and many more cases of changing shift cables and housings, I’ve only owned one bike that had the rear derailer cable route across the down tube and down the seat stay, all others (except my electronic bikes) have had the housing stop mounted on top of the drive line chainstay, or were an internal cable routing with a housing stop on the seat stay. In those instances, the precut housings were the correct length and worked just fine.
For non Shadow type RD, the normal pre-cut Shimano segment for the RD is longer than the length that is done in the OT-RS900 (which is only 240mm). The RS900s are shorter and designed specifically for the road Shadow RD which has a different cable entry location.
If you have a frame with sorta normal cable routing & stops, (above or below the chainstay),
and a standard index type RD (pre-Shadow), it would be surprising if a 240mm length housing would give you proper routing without tight bends or angle at the RD.
Older pre-slant parallelogram RDs, (old Campy style), also had cable entry locations that didn't have a "U" shaped RD housing segment.