TT bike on trainer vs XC Crit racing real world

Hello All,
I’ve been a listener of the podcast intermittently for a couple of years and recently returned to semi consistent training with trainer road after back issues and a ridiculous amount of work travel.
My question is due to the fact my TT bike and roadie have different cassette I solely use my TT bike for trainer road sessions. Does this hamper my ability to train for XC and Criterium racing due to body positioning or is this approach fine. I hold TT position for my work our entirety (including rests).
Should I do a ramp test on each bike to work my bike fit FTP for racing or is this an over thought?
My current FTP is 256w at 84 Kgs which has increased from 230w at 89kg in the space of a month.
My previous best FTP was 315w at 80kgs so I’m heading in the right direction regardless.
Thanks in advance.

I can tell a difference when I train on my road bike and then try to race XC. Does not seem like that should happen, but my N=1 shows that it does. Since my focus is XC, I train on that.

If cassette is the issue, change one over for the training.

If you do both, try changing between the bikes and see how each feels. I would just use each as I race on them so you can get used to the nuances of each. I would not FTP test for each.

Great job on increasing your FTP!

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In XC and Crit racing, you won’t be racing to a prescribed power, but in TT you likely will. You might find that you have a different FTP on your TT bike as opposed to your road or MTB, but as you will be riding more to power on your TT bike, I’d just leave that on and not worry about it.

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Are you training for a TT or that just happens to be the bike that works best on the trainer?

If you are training for a TT and the other disciplines then I would probably do 1/3 to 1/2 of my workouts on the TT bike in aero and the rest (probably VO2 max) at least on the bullhorns, if not on the other bikes.

If you’re not training for a TT then I would at least do all of the work sitting in the bullhorns. Training in the aero position and not racing TTs seems like you are just unnecessarily capping your ability. And if possible change your saddle and bar position to most closely match that of either your road or MTB. But the ideal scenario would be to to train the bike that your are most important races will be on.