Hey, so my tires are constantly going flat and it's getting annoying. I have a Schwinn bike that's meant for riding on the road and a little bit of off road. The tires are a little less rugged than a mountain bikes. I was wondering what I can do to make the tires stronger, is there something I can put within the tire itself? The tiniest of pebbles will cause a flat tire. Should I get new, stronger rubber tires altogether? And these tires don't just go flat in a week, one pebble and I'll have a flat the next day after pumping air in the day before. Thanks!