I want to install a CS-HG800-11 cassette on my Zipp 303s wheelset. The cassette comes with a low spacer (Y4T724000) and I am not sure whether I need it and if so which way should I put it on the freehub body? On side of the spacer is flat the other one is not. Help would be nice!
You don’t say what size the cassette is but presumably it is a wide range model.
11 speed compatible freehub bodies are 1.8mm longer than 8-10 speed ones. Some wide range 11 speed cassettes can fit on a 10 speed freehub because the the large diameter inner sprockets can overhang the inner end of the freehub body a little and clear the drive side flange and spokes. Such cassettes come with a 1.8mm spacer for installation on a 11 speed freehub.