I got back on the bike several years ago at 290lbs. The first 4 mile ride (to work) made me want to puke. After a week of doing it I was fine and I did it most days for 18 months. Got down to 200lbs at one point but injuries helped me back to 270. At 270lbs I had 2 cycling holidays last year in the mountains. It's hard work but not impossible - my friends are tolerant enough to wait for me. I max out at about 12% gradient though and then only for short distances.

Pete