You think you're some kind of expert just because you've got a few opinions? Newsflash: cycling isn't about being "joint-friendly" for overweight individuals, it's about being a hell of a lot better than sitting on the couch. And yeah, it's low-impact compared to running, but that's not the point. The point is that it's a great way to get moving, and if you're too scared to try it because of your joint worries, then maybe you should just stick to walking.