I have Bontrager hard case tires along w/ some silicon-ish lining which is designed to prevent punctures. The tires are always filled between 100 and 110 psi. I only ride streets. I'm getting constant flats. What's causing this? I'm changing out a tube a week. I checked the rims and they appear to be fine. How many flats do you guys get in a month? I think this is excessive, but I don't know.