Shadow-style road rear derailleurs from Shimano require a specific housing section for the final loop into the cable adjuster, and the OT-RS900 is what fills that gap. Standard OT-SP41 housing is too stiff to bend through the tight radius that R9100, R8000, RX800, and R7000 derailleurs demand between the frame and the barrel adjuster, and that stiffness translates directly into notchy shifting and a barrel adjuster that fights you when you try to fine-tune indexing. The 240mm segments of OT-RS900 use a more flexible coil construction that follows the tight curve without binding.

Each piece is 4mm in diameter and comes pre-lubricated internally with low-friction silicone grease, so the inner cable slides freely from the moment you install it. Shimano is explicit that this housing belongs only on the rear derailleur loop — the rest of the shift run should stay on OT-SP41, where the bends are gradual and the stiffer housing holds indexing crisp. Using OT-RS900 elsewhere on the frame introduces compression under shifter load and softens shift feel.

This is a 10-pack, which is why most of our customers buying it are either building up multiple bikes, running a home workshop that services friends' bikes, or just tired of hunting for a single segment every time a rear derailleur gets swapped. Shimano used to include a piece of this housing in the box with new Dura-Ace, Ultegra, GRX, and 105 rear derailleurs, but that stopped being reliable a few years back, and if you didn't get one, standard housing won't work in that location.... Read More