Chain skipping (Suito bought from Zwift) during set up

I bought the Suito trainer from Zwift. I am ridiculously new. The bike I wanted to put on I just got in July, a 9 speed Trek Check Point AL3. It has a 12 x 142 axle. The included thru axle didnt seem to work (axle was not long enough) so I ended up putting the original axle back in and left the spacers in. Ok that seemed stable. Now the the chain seems to be jumping every time I start changing to a larger cog from the back smallest. I bought this trainer not to change the cassette. Do I need to tighten the chain? Am I going to mess up an almost brand new bike to make this fit? (and some of this is responding to advise when I did a search)

First thing is to make sure the spacing is correct. If your cassette is centered correctly then It sounds like you may need to “index” the rear derailleur. When not indexed properly your rear derailleur is just slightly off to one side or the other and you would have problems shifting and you could also jump up or down a gear.
When your chain is on a cog in the middle of your cassette it should be dead centered on that cog.

The suito pre installed cassette has a different number of gears than your bike (11?). You need to replace the one included with a 9 speed like your bike has


Yes, if you trainer came with an 11 speed rear cassette I am not even sure you can put a 9 speed bike on there but that is all spacing. The 9 speed width of the rear dropouts is not as wide as an 11. At a minimum you will need to put the 9 speed cassette on the trainer in order for the chain to work. If you try to run a 9 speed chain on an 11 speed cassette I am not sure it would shift at all because the chain is too wide. Let us now if you get it all working.

I really was clueless trying to put this together. My reading skills are on me but there were definitely some “everyone knows that, who why be direct” moments that I didnt appreciate. Fixed problem of cassette and things worked. Now my three smallest gears in back are having a problem keeping the chain back and forth. Above that it is fine. Yes, the Im on the largest chain ring. Do I play with the tension in the line to the derailleur ?

It sounds like you need to index or slightly adjust the tension on your rear derailleur. This is done with the barrel adjustment knob where the cable meets you rear derailleur. Typically you will have trouble either shifting down or up but not both.

Thanks! It worked!

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