What is the overall advantage/disadvantage bewteen a 23 vs. 25 size tire?

What is the overall advantage/disadvantage bewteen a 23 vs. 25 size tire?

All things equal, a 25 should have slightly less rolling resistance, slightly more weight, and slightly more drag. You'll go just about the same speed either way. If you're riding clinchers, an advantage of a slightly wider tire is the ability to drop a bit of pressure without increasing the risk of pinch flats--this can make the ride a bit smoother ride on rough roads (which is partly why many folks like to go a bit bigger for either commuting, winter riding, or both). They may seem to handle a bit differently too--try each one (holding the make and model constant) and see what you think. If so, try playing around with small differences in tire pressure to see if you can find a sweet spot for each size.

Thanks for the reply.

I'm currently riding on a set of Continental GP4000's (23c). I'm very impressed with how smooth the feel and would be interested to see if there is such a thing as anything better?

I went from a 23 to a 25 Kevlar tire this year. I think it's a little smoother riding and slightly slower. If I had to do it again, I'd buy a 25. I haven't worn out by 23 so next spring I'll put them on and try them out again.