Road bike on trainer without derailleurs

I have a fully built road bike on a Tacx Neo2, and I’d like to take that bike’s derailleurs for another bike build, but leave the bike on the Tacx without the derailleurs as a dedicated trainer bike. What’s the best way to setup the trainer bike in this case? Would I just size the chain using the small front chain ring and a cog in the middle of the rear cassette? If so, how do you size it in that case? Is it like sizing a chain for a fixie? I haven’t don’t that so whatever guidance anyone has for the chain sizing or this approach in general would be appreciated. Thanks!

There are a few ways to do this.

  1. The no extra stuff way. The least successful way - Size your chain with the least amount of slack in the middle of the cassette. You really don’t want anything more than a 1/4" of up and down slack in the chain. This is not like a fixie because there is no way to adjust the chain. You just have to hope that your cassette, chain, and chainring, as well as the distance between all this, all play well together here. Remeber that you can only adjust the chain by the length of two links at a time. There’s not much wiggle room here.

  2. Ghost ring - use an old chain ring in between the chain. You can move it fore and aft to find a spot that takes up enough slack. Rolling in Boston · Installing a “Ghostring” on a Single Speed or Internally Geared Bicycle

  3. Chain tensioner or old derailleur - This is really the best way. The chain tensioner is the best way but the derailleur hack can work too.


A single speed chain tensioner is really cheap, less than £20 for sure.

I’ve tried SS without one and it was sketchy under power. At least if you’re inside the ground is slightly less abrasive!

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Thanks for the great info!

WIll this be a long-term setup? If so, I’d get a SS tensioner. Might also swap the cassette for a single cog and spacers. Otherwise, one of the bodges listed above might work as a stop-gap.

Alternative, just buy a cheap RD. Of course, if you’re AXS or Di2, you SOL there.