Shimano 11-23 to 12-25
 

I just bought a set of SRAM s80's for my tri bike....I'd like to keep my stock wheels on for training and switch out the s80's for racing. To make the change simple, I am going to buy a new cassette to put on the s80 rear. My current cassette is 11-23. Is there a problem w/ buying a 12-25 for the s80, or should I stick w/ buying another 11-23? Are there advantages with a 12-25?

if anything you should put a 12-25 for training and a 12-23 for racing. with a 12-25 you should be able to climb higher hills easier, so for triathlon..........no.

No tech reason why the 12-25 won´t work.
As for advantages/disadvantages..... erm, depends on the course! I train in a hilly area so have a MTB 11-28 cassette.
Are you running compact cranks?

Yes, I have compact double crank.....Shimano Ultegra 39/53.

that's not a compact...