I love to ride on an off-road, usually trips of 1-3 miles at a time. I weigh 200 lbs and do not 'dog' my bikes out- I ride responsibly. BUT my back tires go flat ALL THE TIME. This is a major nuisance so I'm looking to buy a nice bike that rides well, is comfortable, and has lowered chances of popping a back tire. If that means shocks, or some special tire types, I'm willing to pay a little more for a sturdier/hardier bicycle. Any help would be very appreciated. Thanks.