How to get a 7-speed bike with a freewheel on a direct drive trainer My wife has a 2017 Specialized Alibi Step Through. Specs can be found here: https://www.specialized.com/us/en/alibi-step-through/p/154232?color=&amp;searchText=B6617-7402
I have recently ordered a Tacx direct drive trainer. While I should have no problem getting my own bike with a 11-speed cassette on the trainer, I believe my wife's bike will have problems. I'm trying to find the cheapest solution to get her bike on.
I've read the following related posts:
https://www.reddit.com/r/Zwift/comments/fgap31/7_speed_cassette_on_a_direct_drive_trainer/
7 speed cassette on a direct drive trainer from freewheel bike
But I still have doubts. First of all, from these posts it sounds like I just need to get a 7-speed cassette with some spacers to fit a 9/10/11 speed compatible trainer. But as my wife's bike has a FREEWHEEL, the hub should not accept a cassette. Please correct me if I'm wrong here.
Also, let's say a cassette and some spacers were really all I needed, and I have my bike shop to adjust the shifting/derailleurs for me to get the bike on a trainer. Do I need to adjust the shifting/derailleurs again if my wife wants to ride outdoors?
As Daniel Hicks said in his comment, it doesn't matter what's on her bike's wheel. The problem will be that her drivetrain is set up for 7 speeds, and you'll be putting an 11-speed cassette on the trainer. So shifting for her will be rough at best.
With a smart trainer, if you only ride it in erg mode, it doesn't matter what gear you're in. So if there's one gear on her bike that runs smooth when on the trainer (there might be, which would be a lucky coincidence, otherwise you'll need to tweak the barrel adjuster every time she changes between the trainer and the rear wheel), and she only uses the trainer in erg mode and always shifts into that one gear, then you don't need to do anything at all.
The other options are:

upgrade the drivetrain on her bike, and it sounds like that will include upgrading the rear wheel. (It might actually be cheaper to replace the whole bike.)
change the trainer between an 11-speed and 7-speed cassette every time you swap bikes. I believe that 7-speed cassettes and freewheels all have the same spacing.

One option costs more in money, the other in time and annoyance.