I use 25c Armadillos front and rear at 125 psi. They work great. Specialized will replace them too if you get a flat, as I found out. Now that is service. I got my first flat (piece of glass) when the tires only had 200 miles on them. Took the offending tire to a bike shop, grabbed a new one, and was out the door! No other flats now for 1,000 or so miles, hopefully the first was a fluke. I definitely gained a little speed going from the stock 35c tires too.