Originally Posted by
myth001
The front stays the same at 52/36. The smaller on the rear also stays the same. I was just worrying if the change from 28 to 25 on the rear larger cog will make too much of a difference to make the chain slack.
The chain is not new/old (well, it's KMC X11 SL, with about 8000 clicks on it, so I believe it still has life in it). It's well kept though.
8000 miles? 8000 km?
Is this a long term use of the new cassette, or just for a few days?
I'd go ahead and put on a new chain with your new cassette. Much of your cassette wear will be due to a stretched chain, whether it is 1/32" or 1/16" per foot, or more.
If you're planning on using both 25T and 28T cassettes, then size for the larger cassette.