On my old Centurian David Scott bike, I use to put 110 in the front and 115 in the back tire, they were Michelins baldies. I use to ride all over San Francisco, up and down hill and yes, mountians too. Over some very bad streets and got very few flats. Oppose to when had 120 front and back, had quite a bit of flats and the ride was much stiffer and harder on the seat, if you know what I mean...
Peace
TQ