Swapping out cassette

hello i currently have a 50-34 11-34 set up. I want to know if I can just swap out 11-34 with a 11-30 without changing anything else besides the cassette?

Yes, swap away. I use a Wahoo Kickr and swap cassettes without needing to set anything in Zwift.

ah my bad i didnt say it was for my bike not my trainer.

You will need to adjust b limit at minimum. If your chain length is setup correctly with the 34, it may well need a link removed otherwise you risk your chain being too slack. Best to check chain length AFTER installing new cassette and adjusting B limit as it might well be fine. This applies to both trainer and bikes.

The Shimano chain sizing method, often called “big-big-plus 2”, is to run the chain on the largest chainring, the largest cog, no derailleur, and add 2 links (hence the name). Changing from 34T to 30T would probably mean taking 2 links out. This said, the drive train may work very well without shortening the chain, in particular if you have a longer cage derailleur.

The Shimano sizing method bypasses the derailleur, so B limit screw adjustment would take place after the chain size is set.

Shimano manual is not what bike shops follow as it can be needlessly costly for customers :wink:

It’s also the method Park Tools recommends. And Sheldon.

Not sure how chain sizing can influence the cost…

Oh dear - Remove links, move bike off trainer back to road wheel. Oops, too short. Rejoin links… amateur hour.

2 seconds to set B limit without destructive link removal. The internet isnt always the smartest!

I assume you missed this part.

There’s nothing destructive in removing chain links.

Metal fatigue. But anyway …