I read that they are faster as you can run a slightly lower pressure and then have a better contact patch on the road, whilst not losing speed from bouncing over the road too. Described better online though. Lol.There is a school of thought that 25's can be faster than 23's for aero reasons. My new wheels are 25mm width 50mm deep section rims and I am tempted to try 25's although I normally run a 23 tyre