205lb rider - 23 vs 25mm wide tires?

This doesn't make much sense to me - How would a bigger tire have less contact with the road? Generally, a the purpose of having a wider tire is to increase your contact patch and/or ride quality (because of larger air volume).

I forget where I read this, I might be way off in left field, but I heard that a 25 on the rear and 23 on the front is best because of the way the tire contacts the ground.  the rear is more of a smaller wider circle better for transfering crank force and the front is a longer narrower oval better for turning traction.  Im sure someone will correct me if Im wrong.

Good question, this is one of those areas of tri-equipment that we just kind of take for granted and never reconsider the 23's that came on the bike.

Short answer: 25's CAN be faster. Longer answer: It depends. There are several variables to consider:

- Weight. 25's will weigh more than 23's

- Rolling resistance. 25's will roll with less deformation in the direction you are going, resulting in lower resistance. (The total deformation will be the same, just more of it will be lateral deformation).

- Aerodynamics: No clear answer here. Common sense says a more narrow profile would be more efficient, but aerodynamics are funny. Probably depends on your fork, frame, etc as to whether 23 or 25 is more aerodynamic.

- Comfor. 25's are more comfortable (smooth) than 23's, that's unanimous. 

- Durability. (if that's the right word). 25's are slightly less susceptible to pinch flats than 23's. 

- Availability. 25's are much less readily available than 23's, and in many fewer rubber compounds.  

One thing (amongst many) that I do not know, and would be curious to find the answer to is: if you have a 25 rim, can you run a 23 tire on it?  I know the tubes are good, but don't know about the tire. This would likely be the scenario if, say, you cut a tire on your warmup ride at a race...chances are pretty good you won't find a spare 25 laying around, and would be forced to go with a 23.

I confirmed my understanding of this here, but there are more resources available everywhere.  Google will give you many more resources on this, it's been pretty thoroughly researched.

I have a question concerning the 25s. I am close to 200 and ride 23s and I constantly get pinch flats no matter how often I check my tire pressure. I ride on the roads of chicago to get to my trails and that is when I always get them. (search for my post on tubes) Am I able to upgrade to a 25 tire with my current wheel or do I need to upgrade my wheel too? Needless to say over the last few months I have gotten really good at changing tubes and patching tubes in order to save money.