It depends on what kind of trainer you want to use. If it is a direct drive trainer that is compatible with thru axles, such as the Wahoo Kickr, you do not need anything. If it is a wheel on trainer then there are two options I am aware of. The first, is you can replace the RAT Derailleur hanger with a Cervelo threaded derailleur hanger (part# DRH-WMN112) and then use any 12mm x 142mm x 1.75mm through-axle adapter for a standard or direct-drive trainer. That comes directly from a Cervelo service bulletin. The threaded hanger can be ordered from a Cervelo dealer. The second option is using The Robert Axle Project thru axle for Focus bikes which uses the same RAT system. You can find it at https://robertaxleproject.com/...ner-focus-rat-bikes/
. I have not used the Robert Axle Project axle but I have used the threaded Cervelo derailleur hanger with a Kinetic thru axle trainer skewer.
Fit2Ride Velo Studio http://www.fit2ridevelo.com