I'm 330 lbs. I started riding 5 years ago and I was close to 400 lbs. I bought a Surly LHT, a great bike for a heavy rider. I started out riding 3 mile loops. I wore jeans and a t-shirt. I worked up to longer rides, bought a Specialized Roubaix, got a proper lycra kit, and I put 7000 miles on it. I dropped 100lbs, put 30 back on, and so on. I haven't ridden much this year due to an injury, and I don't have the Roubaix anymore, but I rode an old Moser steel road bike today on a quick 12 mile ride with a couple sharp climbs over 8% and I was surprised that I didn't totally suck. I'll never climb 3000m in a day, but it's perfectly possible to be heavy and ride around for a few hours and thoroughly enjoy yourself. Will you get the occasional rude comment? Sure. But it's better than staying inside and fretting about yourself.