My girlfriend has a diamond back insight 1 hybrid, and one day we noticed her tire get flat, We pumped it up continued the trip, when we finish flat again. So I changed the tired... and it occurrs again, I have gone through 5 tires, and apparently what happens, after the night passes the tire is flat in the morning, but a quick pump up fixes it for the day. What should i look for as the cause of the problem? Im kind of afraid to tighten the presta valve too much as i broke some on 2 tires changes before, right after putting them on!!
we live in san diego so i dont think cold air is the problem, at that both tires would deflate..