Changing cassettes: do I need to shorten my chain.
 

The bike I ordered has a 11-28 cassette and I'd like to switch to a 12-25. Should I take a link out of the chain? The calculator on epicidiot.com says 54 links for both but the machineHead site says 53 links for the 12-25. The largest chainring is 53 and the chain stay is 40.5cm. If I do, it's an ultegra 10 speed chain. Is it just a matter of removing the link with the chain tool and getting a new pin? Thanks.

No change in chain length is required because your new cassette fits entirely within your original one. You already know the chain works on a 12t or 25t sprocket so what difference can the cassette make?

Thanks. I wasn't sure if it would affect shifting.

Any change, IF even possible, is so minimal, it really isn't worth it.
You would theoretically shorten the chain by 3/4".
There's a 25% chance you don't have the necessary "excess" on your current chain, since you can only shorten in 1" increments.

IOW, don't bother.
You'll also have the option of throwing the old cassette back on without having to "re-lengthen" the chain.

IF you were going from a 32-34T cog to a 25, I'd definitely say shorten it.

I have just changed my rear cassette the same as your doing, I left the chain as it was with no problems.

No sweat. It won't affect shifting, any more than if you only rode between the 12t and 25t sprocket you already have on the existing cassette. If they work fine, than so will any sprocket on this cassette.

But you need to install a new chain with your new cassette.
and anticipate changing the chain again ,
before you wear the cassette down, too quickly..

package the old chain and cassette together if you want to revert back to it.

get a quick link to join the chain, and then they can be reused..

I used to know the answer to tnat but it may have changed. Back in the old days it depended on whether you used Campy or Shimano components.

Campy recommended sizing the chain using the little/little method. While there's a 1 tooth difference in your little/little, you can't grow your chain by that little so you'd be good-to-go. The advantage of that method is that, if you ever switch back to an 11/28 cassette, you'd still be good-to-go.

Shimano recommended using the big/big method. Even so, I kind of doubt a 3 tooth difference would be enough to require shortening your chain.

No he won't. A change is only needed if the original cassette has significant wear. In this case the OP is simply swapping a new cassette for another new cassette.

You there? I don't read into the OP post that there is zero miles on the drive train.
yea, throw the cassette on and see if its oK..

Still like quick links rather than the break off chain pin shimano sells.

He pretty much infers that in the FIRST sentence of his post!
"The bike I ordered has a 11-28 cassette and I'd like to switch to a 12-25."