A bike shop (whom I trust) replaced my tires with new 700X25c Pirelli P Zero Zello 4S front and rear, the rear tire did not clear the fork/frame for some reason, they switched the rear 700X25c with 700X23c. Now I have 700X25c on the front and 700X23c on the rear. It seems strange having a larger tire on the front and thinner tire on rear, as I have always and previously run 700X25c Continentals on both front and rear, although from an engineering point of view I have no substance to object, and they advised they do in fact run 700X25c front and 700X23c on new models of some of their Giant bikes. I have not ridden the tires enough yet to determine whether there is an issue, it just seems odd. Can someone who is technically endowed on this matter please advise me on whether this is appropriate.