Cassette Size


Can I fit an 11-30T cassette to my bike, whilst having an 11-28T on my turbo trainer? Will this cause any issues?

Will I have to regear the bike every time I switch cassettes on it?


Should be ok. I imagine you’ll be using a common chain (length) sized to work for both setups – just carefully check everything is cleanly shifting while pedaling gently and slowly, before getting on and hammering away.

Ideally you’d want to check your B Screw adjustment but it’s possible you can set it for the 30T and it’ll still work ok on the 28T.

it’ll be fine as they are going from a bigger largest sprocket to a smaller one.


Ah. I was reading it as the 30T being new.

What derailleur are you running? I’d guess your chain and derailleur will be able to handle both, at least nominally. Those cassette sizes shouldn’t be a breaking point for most derailleurs. But you could run into shifting problems.

Check the big-big combo when you have the 11-30 installed (chain on big ring in the front, and on the 30 in back). If it’ll shift into that cog in back (it should only 2 teeth difference), look at the derailleur. It might be pulled a lot farther forward than is ideal, which could degrade your shifting. It might not be though, it might work okay.

Then check the small-small combo when you have the 11-28 installed. The risk here is that the chain might be too slack, might jump around and shift badly, or jump off the cog and into the chainstay. Or it might not, it might work okay :slight_smile:

As others have said, the other issue for shifting might be the B screw. A poorly set B gap can mess with your shifting too, and it’s much more likely the higher end your groupset is. It’s possible you could find a B gap that will lead to good shifting on both cassettes, the difference isn’t all that big. But I’ve seen derailleurs that are so sensitive, an 1/8th turn of the B screw is the difference between good and spotty shifting.

So my guess would be the chain and derailleur can function with both, but the most likely issue, if there is one, would be shifting issues due to the B gap.

But it may all work just fine too :person_shrugging: :smiley:

I’ve run with different cassettes in the past (11-30 and 11-32) on my bike and trainer. If you have already had the larger cassette on then you should be fine. If you had the smaller one on then there is a chance your chain is too short to accommodate the larger cassette. I never had to adjust the rear derailleur and it worked fine with both.