25t to 28tm same chain length?

[tuxbailey]

I switched the cassette from 11-25 to 11-28 and found that the existing chain works fine, even though I was ready to put a new chain on.

does 3t not make any difference for the chain?

[Veloo]

My two cassettes have 25 and 27 and I use the same chain.
I'd think you're good with a delta of 1 tooth.

[Dave]

3T requires 3/4 inch more chain, but if the length was set to the maximum, with the little/little method, it will handle the RD's maximum wrap capacity.

[Ken Robb]

I think you may have been near the long limit with the 25t and now are near the short limit with the 27t so lucky you!