Slightly off-topic from the discussion of 9 speed cassettes, here’s a post, for reference for anyone reading this thread who’s interested in using a 7 speed drivetrain on a modern wheel-off trainer:
7 Speed Bike on Wheel-off Trainers: Your seven speed bike will probably work on a modern direct drive trainer. There’s a YouTube video showing the concept and the adjustment that is needed for a seven speed cassette versus what’s needed for an eight, nine or ten speed cassette. Those 8, 9 and 10 speed cassettes will go straight onto the 11 speed direct drive trainer with a simple adapter. For 7 speed use, you need to add a second spacer, 4 or 4.5 MM, and file a couple of small indents in the aluminum spacer. Our local bike shop provided a 4mm spacer for a couple of dollars and we’ve been using a 7 speed triple from the 90s on a 2014 Wahoo KICKR for months.Here’s a video that helped me:
How To Install 7 Speed Cassette On 8/9/10 Speed Hub
